--- /dev/null
+\input texinfo
+@c %**start of header
+@setfilename omni-utils.info
+@settitle @sc{gnu} Omni-utils
+
+@c %**end of header
+
+@include version.texi
+@include constants.texi
+
+@c Define new indices.
+@defcodeindex op
+@defcodeindex fl
+
+@c Put everything in one index (arbitrarily chosen to be the concept index).
+@syncodeindex fl cp
+@syncodeindex fn cp
+@syncodeindex ky cp
+@syncodeindex op cp
+@syncodeindex pg cp
+@syncodeindex vr cp
+
+@ifinfo
+@format
+START-INFO-DIR-ENTRY
+* @sc{gnu} Utilities: (omni-utils). @sc{gnu} Utilities.
+* Common options: Common options.
+* File permissions: Access modes.
+* Date input formats: Specifying date strings.
+* Opening the software toolbox: The software tools philosophy.
+* GNU Free Documentation License: The license for this documentation.
+
+* basename: (omni-utils)basename invocation. Strip directory and suffix.
+* cat: (omni-utils)cat invocation. Concatenate and write files.
+* chgrp: (omni-utils)chgrp invocation. Change file groups.
+* chmod: (omni-utils)chmod invocation. Change file permissions.
+* chown: (omni-utils)chown invocation. Change file owners/groups.
+* chroot: (omni-utils)chroot invocation. Specify the root directory.
+* cksum: (omni-utils)cksum invocation. Print @sc{posix} CRC checksum.
+* comm: (omni-utils)comm invocation. Compare sorted files by line.
+* cp: (omni-utils)cp invocation. Copy files.
+* csplit: (omni-utils)csplit invocation. Split by context.
+* cut: (omni-utils)cut invocation. Print selected parts of lines.
+* date: (omni-utils)date invocation. Print/set system date and time.
+* dd: (omni-utils)dd invocation. Copy and convert a file.
+* df: (omni-utils)df invocation. Report filesystem disk usage.
+* dir: (omni-utils)dir invocation. List directories briefly.
+* dircolors: (omni-utils)dircolors invocation. Color setup for ls.
+* dirname: (omni-utils)dirname invocation. Strip non-directory suffix.
+* du: (omni-utils)du invocation. Report on disk usage.
+* echo: (omni-utils)echo invocation. Print a line of text.
+* env: (omni-utils)env invocation. Modify the environment.
+* expand: (omni-utils)expand invocation. Convert tabs to spaces.
+* expr: (omni-utils)expr invocation. Evaluate expressions.
+* factor: (omni-utils)factor invocation. Print prime factors
+* false: (omni-utils)false invocation. Do nothing, unsuccessfully.
+* fmt: (omni-utils)fmt invocation. Reformat paragraph text.
+* fold: (omni-utils)fold invocation. Wrap long input lines.
+* groups: (omni-utils)groups invocation. Print group names a user is in.
+* head: (omni-utils)head invocation. Output the first part of files.
+* hostid: (omni-utils)hostid invocation. Print numeric host identifier.
+* hostname: (omni-utils)hostname invocation. Print or set system name.
+* id: (omni-utils)id invocation. Print real/effective uid/gid.
+* install: (omni-utils)install invocation. Copy and change attributes.
+* join: (omni-utils)join invocation. Join lines on a common field.
+* ln: (omni-utils)ln invocation. Make links between files.
+* logname: (omni-utils)logname invocation. Print current login name.
+* ls: (omni-utils)ls invocation. List directory contents.
+* md5sum: (omni-utils)md5sum invocation. Print or check message-digests.
+* mkdir: (omni-utils)mkdir invocation. Create directories.
+* mkfifo: (omni-utils)mkfifo invocation. Create FIFOs (named pipes).
+* mknod: (omni-utils)mknod invocation. Create special files.
+* mv: (omni-utils)mv invocation. Rename files.
+* nice: (omni-utils)nice invocation. Modify scheduling priority.
+* nl: (omni-utils)nl invocation. Number lines and write files.
+* nohup: (omni-utils)nohup invocation. Immunize to hangups.
+* od: (omni-utils)od invocation. Dump files in octal, etc.
+* paste: (omni-utils)paste invocation. Merge lines of files.
+* pathchk: (omni-utils)pathchk invocation. Check file name portability.
+* pr: (omni-utils)pr invocation. Paginate or columnate files.
+* printenv: (omni-utils)printenv invocation. Print environment variables.
+* printf: (omni-utils)printf invocation. Format and print data.
+* ptx: (omni-utils)ptx invocation. Produce permuted indexes.
+* pwd: (omni-utils)pwd invocation. Print working directory.
+* rm: (omni-utils)rm invocation. Remove files.
+* rmdir: (omni-utils)rmdir invocation. Remove empty directories.
+* seq: (omni-utils)seq invocation. Print numeric sequences
+* shred: (omni-utils)shred invocation. Remove files more securely.
+* sleep: (omni-utils)sleep invocation. Delay for a specified time.
+* sort: (omni-utils)sort invocation. Sort text files.
+* split: (omni-utils)split invocation. Split into fixed-size pieces.
+* stty: (omni-utils)stty invocation. Print/change terminal settings.
+* su: (omni-utils)su invocation. Modify user and group id.
+* sum: (omni-utils)sum invocation. Print traditional checksum.
+* sync: (omni-utils)sync invocation. Synchronize memory and disk.
+* tac: (omni-utils)tac invocation. Reverse files.
+* tail: (omni-utils)tail invocation. Output the last part of files.
+* tee: (omni-utils)tee invocation. Redirect to multiple files.
+* test: (omni-utils)test invocation. File/string tests.
+* touch: (omni-utils)touch invocation. Change file timestamps.
+* tr: (omni-utils)tr invocation. Translate characters.
+* true: (omni-utils)true invocation. Do nothing, successfully.
+* tsort: (omni-utils)tsort invocation. Topological sort.
+* tty: (omni-utils)tty invocation. Print terminal name.
+* uname: (omni-utils)uname invocation. Print system information.
+* unexpand: (omni-utils)unexpand invocation. Convert spaces to tabs.
+* uniq: (omni-utils)uniq invocation. Uniquify files.
+* users: (omni-utils)users invocation. Print current user names.
+* vdir: (omni-utils)vdir invocation. List directories verbosely.
+* wc: (omni-utils)wc invocation. Byte, word, and line counts.
+* who: (omni-utils)who invocation. Print who is logged in.
+* whoami: (omni-utils)whoami invocation. Print effective user id.
+* yes: (omni-utils)yes invocation. Print a string indefinitely.
+END-INFO-DIR-ENTRY
+@end format
+@end ifinfo
+
+@ifinfo
+This file documents the GNU command line utilities.
+
+Copyright (C) 1994, 95, 96, 2001 Free Software Foundation, Inc.
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.1 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
+Texts. A copy of the license is included in the section entitled ``GNU
+Free Documentation License''.
+
+@end ifinfo
+
+@titlepage
+@title @sc{gnu} @code{Omni-utils}
+@subtitle A set of command line utilities
+@subtitle for version @value{VERSION}, @value{UPDATED}
+@author David MacKenzie et al.
+
+@page
+@vskip 0pt plus 1filll
+Copyright @copyright{} 1994, 95, 96, 2000 Free Software Foundation, Inc.
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.1 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
+Texts. A copy of the license is included in the section entitled ``GNU
+Free Documentation License''.
+@end titlepage
+
+
+@c If your makeinfo doesn't grok this @ifnottex directive, then either
+@c get a newer version of makeinfo or do s/ifnottex/ifinfo/ here and on
+@c the matching @end directive below.
+@ifnottex
+@node Top
+@top GNU Omni-utils
+
+@cindex text utilities
+@cindex shell utilities
+@cindex file utilities
+This manual documents version @value{VERSION} of the @sc{gnu} command
+line utilities.
+
+@menu
+* Introduction:: Caveats, overview, and authors.
+* Common options:: Common options.
+* Output of entire files:: cat tac nl od
+* Formatting file contents:: fmt pr fold
+* Output of parts of files:: head tail split csplit
+* Summarizing files:: wc sum cksum md5sum
+* Operating on sorted files:: sort uniq comm ptx tsort
+* Operating on fields within a line:: cut paste join
+* Operating on characters:: tr expand unexpand
+* Directory listing:: ls dir vdir d v dircolors
+* Basic operations:: cp dd install mv rm shred
+* Special file types:: ln mkdir rmdir mkfifo mknod
+* Changing file attributes:: chgrp chmod chown touch
+* Disk usage:: df du sync
+* Printing text:: echo printf yes
+* Conditions:: false true test expr
+* Redirection:: tee
+* File name manipulation:: dirname basename pathchk
+* Working context:: pwd stty printenv tty
+* User information:: id logname whoami groups users who
+* System context:: date uname hostname
+* Modified command invocation:: chroot env nice nohup su
+* Delaying:: sleep
+* Numeric operations:: factor seq
+* File permissions:: Access modes.
+* Date input formats:: Specifying date strings.
+* Opening the software toolbox:: The software tools philosophy.
+* GNU Free Documentation License:: The license for this documentation.
+* Index:: General index.
+
+@detailmenu
+ --- The Detailed Node Listing ---
+
+Common Options
+
+* Backup options:: Backup options
+* Block size:: Block size
+* Target directory:: Target directory
+* Trailing slashes:: Trailing slashes
+
+Output of entire files
+
+* cat invocation:: Concatenate and write files.
+* tac invocation:: Concatenate and write files in reverse.
+* nl invocation:: Number lines and write files.
+* od invocation:: Write files in octal or other formats.
+
+Formatting file contents
+
+* fmt invocation:: Reformat paragraph text.
+* pr invocation:: Paginate or columnate files for printing.
+* fold invocation:: Wrap input lines to fit in specified width.
+
+Output of parts of files
+
+* head invocation:: Output the first part of files.
+* tail invocation:: Output the last part of files.
+* split invocation:: Split a file into fixed-size pieces.
+* csplit invocation:: Split a file into context-determined pieces.
+
+Summarizing files
+
+* wc invocation:: Print byte, word, and line counts.
+* sum invocation:: Print checksum and block counts.
+* cksum invocation:: Print CRC checksum and byte counts.
+* md5sum invocation:: Print or check message-digests.
+
+Operating on sorted files
+
+* sort invocation:: Sort text files.
+* uniq invocation:: Uniquify files.
+* comm invocation:: Compare two sorted files line by line.
+* ptx invocation:: Produce a permuted index of file contents.
+* tsort invocation:: Topological sort.
+
+@code{ptx}: Produce permuted indexes
+
+* General options in ptx:: Options which affect general program behavior.
+* Charset selection in ptx:: Underlying character set considerations.
+* Input processing in ptx:: Input fields, contexts, and keyword selection.
+* Output formatting in ptx:: Types of output format, and sizing the fields.
+* Compatibility in ptx:: The GNU extensions to @code{ptx}
+
+Operating on fields within a line
+
+* cut invocation:: Print selected parts of lines.
+* paste invocation:: Merge lines of files.
+* join invocation:: Join lines on a common field.
+
+Operating on characters
+
+* tr invocation:: Translate, squeeze, and/or delete characters.
+* expand invocation:: Convert tabs to spaces.
+* unexpand invocation:: Convert spaces to tabs.
+
+@code{tr}: Translate, squeeze, and/or delete characters
+
+* Character sets:: Specifying sets of characters.
+* Translating:: Changing one characters to another.
+* Squeezing:: Squeezing repeats and deleting.
+* Warnings in tr:: Warning messages.
+
+Directory listing
+
+* ls invocation:: List directory contents
+* dir invocation:: Briefly list directory contents
+* vdir invocation:: Verbosely list directory contents
+* dircolors invocation:: Color setup for @code{ls}
+
+@code{ls}: List directory contents
+
+* Which files are listed:: Which files are listed
+* What information is listed:: What information is listed
+* Sorting the output:: Sorting the output
+* More details about version sort:: More details about version sort
+* General output formatting:: General output formatting
+* Formatting the file names:: Formatting the file names
+
+Basic operations
+
+* cp invocation:: Copy files and directories
+* dd invocation:: Convert and copy a file
+* install invocation:: Copy files and set attributes
+* mv invocation:: Move (rename) files
+* rm invocation:: Remove files or directories
+* shred invocation:: Remove files more securely
+
+Special file types
+
+* ln invocation:: Make links between files
+* mkdir invocation:: Make directories
+* mkfifo invocation:: Make FIFOs (named pipes)
+* mknod invocation:: Make block or character special files
+* rmdir invocation:: Remove empty directories
+
+Changing file attributes
+
+* chown invocation:: Change file owner and group
+* chgrp invocation:: Change group ownership
+* chmod invocation:: Change access permissions
+* touch invocation:: Change file timestamps
+
+Disk usage
+
+* df invocation:: Report filesystem disk space usage
+* du invocation:: Estimate file space usage
+* sync invocation:: Synchronize data on disk with memory
+
+Printing text
+
+* echo invocation:: Print a line of text
+* printf invocation:: Format and print data
+* yes invocation:: Print a string until interrupted
+
+Conditions
+
+* false invocation:: Do nothing, unsuccessfully
+* true invocation:: Do nothing, successfully
+* test invocation:: Check file types and compare values
+* expr invocation:: Evaluate expressions
+
+@code{test}: Check file types and compare values
+
+* File type tests:: File type tests
+* Access permission tests:: Access permission tests
+* File characteristic tests:: File characteristic tests
+* String tests:: String tests
+* Numeric tests:: Numeric tests
+
+@code{expr}: Evaluate expression
+
+* String expressions:: <colon> match substr index length quote
+* Numeric expressions:: + - * / %
+* Relations for expr:: | & < <= = == != >= >
+* Examples of expr:: Examples of using @code{expr}
+
+Redirection
+
+* tee invocation:: Redirect output to multiple files
+
+File name manipulation
+
+* basename invocation:: Strip directory and suffix from a file name
+* dirname invocation:: Strip non-directory suffix from a file name
+* pathchk invocation:: Check file name portability
+
+Working context
+
+* pwd invocation:: Print working directory
+* stty invocation:: Print or change terminal characteristics
+* printenv invocation:: Print all or some environment variables
+* tty invocation:: Print file name of terminal on standard input
+
+@code{stty}: Print or change terminal characteristics
+
+* Control:: Control settings
+* Input:: Input settings
+* Output:: Output settings
+* Local:: Local settings
+* Combination:: Combination settings
+* Characters:: Special characters
+* Special:: Special settings
+
+User information
+
+* id invocation:: Print real and effective uid and gid
+* logname invocation:: Print current login name
+* whoami invocation:: Print effective user id
+* groups invocation:: Print group names a user is in
+* users invocation:: Print login names of users currently logged in
+* who invocation:: Print who is currently logged in
+
+System context
+
+* date invocation:: Print or set system date and time
+* uname invocation:: Print system information
+* hostname invocation:: Print or set system name
+* hostid invocation:: Print numeric host identifier.
+
+@code{date}: Print or set system date and time
+
+* Time directives:: Time directives
+* Date directives:: Date directives
+* Literal directives:: Literal directives
+* Padding:: Padding
+* Setting the time:: Setting the time
+* Options for date:: Options for @code{date}
+* Examples of date:: Examples of @code{date}
+
+Modified command invocation
+
+* chroot invocation:: Run a command with a different root directory
+* env invocation:: Run a command in a modified environment
+* nice invocation:: Run a command with modified scheduling priority
+* nohup invocation:: Run a command immune to hangups
+* su invocation:: Run a command with substitute user and group id
+
+Delaying
+
+* sleep invocation:: Delay for a specified time
+
+Numeric operations
+
+* factor invocation:: Print prime factors
+* seq invocation:: Print numeric sequences
+
+File permissions
+
+* Mode Structure:: Structure of File Permissions
+* Symbolic Modes:: Mnemonic permissions representation
+* Numeric Modes:: Permissions as octal numbers
+
+Date input formats
+
+* General date syntax: General date syntax
+* Calendar date items: Calendar date items
+* Time of day items: Time of day items
+* Time zone items: Time zone items
+* Day of week items: Day of week items
+* Relative items in date strings: Relative items in date strings
+* Pure numbers in date strings: Pure numbers in date strings
+* Authors of getdate: Authors of getdate
+
+Opening the software toolbox
+
+* Toolbox introduction:: Toolbox introduction
+* I/O redirection:: I/O redirection
+* The who command:: The @code{who} command
+* The cut command:: The @code{cut} command
+* The sort command:: The @code{sort} command
+* The uniq command:: The @code{uniq} command
+* Putting the tools together:: Putting the tools together
+
+GNU Free Documentation License
+
+* How to use this License for your documents::
+
+@end detailmenu
+@end menu
+
+@end ifnottex
+
+
+@node Introduction
+@chapter Introduction
+
+This manual is incomplete: No attempt is made to explain basic concepts
+in a way suitable for novices. Thus, if you are interested, please get
+involved in improving this manual. The entire @sc{gnu} community will
+benefit.
+
+@cindex @sc{posix.2}
+The @sc{gnu} utilities documented here are mostly compatible with the
+@sc{posix.2} standard.
+@cindex bugs, reporting
+Please report bugs to @email{bug-omni-utils@@gnu.org}. Remember
+to include the version number, machine architecture, input files, and
+any other information needed to reproduce the bug: your input, what you
+expected, what you got, and why it is wrong. Diffs are welcome, but
+please include a description of the problem as well, since this is
+sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
+
+@cindex Berry, K.
+@cindex Paterson, R.
+@cindex Stallman, R.
+@cindex Pinard, F.
+@cindex MacKenzie, D.
+@cindex Meyering, J.
+@cindex Youmans, B.
+This manual was originally derived from the Unix man pages in the
+distributions, which were written by David MacKenzie and updated by Jim
+Meyering. What you are reading now is the authoritative documentation
+for these utilities; the man pages are no longer being maintained. The
+original @code{fmt} man page was written by Ross Paterson. Fran@,{c}ois
+Pinard did the initial conversion to Texinfo format. Karl Berry did the
+indexing, some reorganization, and editing of the results. Brian
+Youmans of the Free Software Foundation office staff combined the
+manuals for textutils, fileutils, and sh-utils to produce the present
+omnibus manual. Richard Stallman contributed his usual invaluable
+insights to the overall process.
+
+@node Common options
+@chapter Common options
+
+@cindex common options
+
+Certain options are available in all of these programs. Rather than
+writing identical descriptions for each of the programs, they are
+described here. (In fact, every @sc{gnu} program accepts (or should accept)
+these options.)
+
+@vindex POSIXLY_CORRECT
+Normally options and operands can appear in any order, and programs act
+as if all the options appear before any operands. For example,
+@samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
+@samp{:} is an option-argument of @option{-t}. However, if the
+@env{POSIXLY_CORRECT} environment variable is set, options must appear
+before operands, unless otherwise specified for a particular command.
+
+Some of these programs recognize the @samp{--help} and @samp{--version}
+options only when one of them is the sole command line argument.
+
+@table @samp
+
+@item --help
+@opindex --help
+@cindex help, online
+Print a usage message listing all available options, then exit successfully.
+
+@item --version
+@opindex --version
+@cindex version number, finding
+Print the version number, then exit successfully.
+
+@item --
+@opindex --
+@cindex option delimiter
+Delimit the option list. Later arguments, if any, are treated as
+operands even if they begin with @samp{-}. For example, @samp{sort --
+-r} reads from the file named @file{-r}.
+
+@end table
+
+@cindex standard input
+@cindex standard output
+A single @samp{-} is not really an option, though it looks like one. It
+stands for standard input, or for standard output if that is clear from
+the context, and it can be used either as an operand or as an
+option-argument. For example, @samp{sort -o - -} outputs to standard
+output and reads from standard input, and is equivalent to plain
+@samp{sort}. Unless otherwise specified, @samp{-} can appear in any
+context that requires a file name.
+
+@menu
+* Backup options:: -b -S -V, in some programs.
+* Block size:: BLOCK_SIZE and --block-size, in some programs.
+* Target directory:: --target-directory, in some programs.
+* Trailing slashes:: --strip-trailing-slashes, in some programs.
+@end menu
+
+
+@node Backup options
+@section Backup options
+
+@cindex backup options
+
+Some @sc{gnu} programs (at least @code{cp}, @code{install}, @code{ln}, and
+@code{mv}) optionally make backups of files before writing new versions.
+These options control the details of these backups. The options are also
+briefly mentioned in the descriptions of the particular programs.
+
+@table @samp
+
+@item -b
+@itemx @w{@kbd{--backup}[=@var{method}]}
+@opindex -b
+@opindex --backup
+@vindex VERSION_CONTROL
+@cindex backups, making
+Make a backup of each file that would otherwise be overwritten or removed.
+Without this option, the original versions are destroyed.
+Use @var{method} to determine the type of backups to make.
+When this option is used but @var{method} is not specified,
+then the value of the @env{VERSION_CONTROL}
+environment variable is used. And if @env{VERSION_CONTROL} is not set,
+the default backup type is @samp{existing}.
+
+Note that the short form of this option, @samp{-b} does not accept any
+argument. Using @samp{-b} is equivalent to using @samp{--backup=existing}.
+
+@vindex version-control @r{Emacs variable}
+This option corresponds to the Emacs variable @samp{version-control};
+the values for @var{method} are the same as those used in Emacs.
+This option also accepts more descriptive names.
+The valid @var{method}s are (unique abbreviations are accepted):
+
+@table @samp
+@item none
+@itemx off
+@opindex none @r{backup method}
+Never make backups.
+
+@item numbered
+@itemx t
+@opindex numbered @r{backup method}
+Always make numbered backups.
+
+@item existing
+@itemx nil
+@opindex existing @r{backup method}
+Make numbered backups of files that already have them, simple backups
+of the others.
+
+@item simple
+@itemx never
+@opindex simple @r{backup method}
+Always make simple backups. Please note @samp{never} is not to be
+confused with @samp{none}.
+
+@end table
+
+@item -S @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -S
+@opindex --suffix
+@cindex backup suffix
+@vindex SIMPLE_BACKUP_SUFFIX
+Append @var{suffix} to each backup file made with @samp{-b}. If this
+option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
+environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
+set, the default is @samp{~}, just as in Emacs.
+
+@itemx --version-control=@var{method}
+@opindex --version-control
+@c FIXME: remove this block one or two releases after the actual
+@c removal from the code.
+This option is obsolete and will be removed in a future release.
+It has been replaced with @w{@kbd{--backup}}.
+
+@end table
+
+@node Block size
+@section Block size
+
+@cindex block size
+
+Some @sc{gnu} programs (at least @code{df}, @code{du}, and @code{ls}) display
+file sizes in ``blocks''. You can adjust the block size to make file
+sizes easier to read. The block size used for display is independent of
+any filesystem block size.
+
+Normally, disk usage sizes are rounded up, disk free space sizes are
+rounded down, and other sizes are rounded to the nearest value with ties
+rounding to an even value.
+
+@opindex --block-size=@var{size}
+@vindex BLOCK_SIZE
+@vindex DF_BLOCK_SIZE
+@vindex DU_BLOCK_SIZE
+@vindex LS_BLOCK_SIZE
+@vindex POSIXLY_CORRECT@r{, and block size}
+
+The default block size is chosen by examining the following environment
+variables in turn; the first one that is set determines the block size.
+
+@table @code
+
+@item DF_BLOCK_SIZE
+This specifies the default block size for the @code{df} command.
+Similarly, @env{DU_BLOCK_SIZE} specifies the default for @code{du} and
+@env{LS_BLOCK_SIZE} for @code{ls}.
+
+@item BLOCK_SIZE
+This specifies the default block size for all three commands, if the
+above command-specific environment variables are not set.
+
+@item POSIXLY_CORRECT
+If neither the @env{@var{command}_BLOCK_SIZE} nor the @env{BLOCK_SIZE}
+variables are set, but this variable is set, the block size defaults to 512.
+
+@end table
+
+If none of the above environment variables are set, the block size
+currently defaults to 1024 bytes, but this number may change in the
+future.
+
+@cindex human-readable output
+@cindex SI output
+
+A block size specification can be a positive integer specifying the number
+of bytes per block, or it can be @code{human-readable} or @code{si} to
+select a human-readable format.
+
+
+With human-readable formats, output sizes are followed by a size letter
+such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
+powers of 1024; @samp{M} stands for 1,048,576 bytes.
+@code{BLOCK_SIZE=si} is similar, but uses powers of 1000; @samp{M} stands
+for 1,000,000 bytes. (SI, the International System of Units, defines
+these power-of-1000 prefixes.)
+
+An integer block size can be followed by a size letter to specify a
+multiple of that size. When this notation is used, the size letters
+normally stand for powers of 1024, and can be followed by an optional
+@samp{B} for ``byte''; but if followed by @samp{D} (for ``decimal
+byte''), they stand for powers of 1000. For example,
+@code{BLOCK_SIZE=4MB} is equivalent to @code{BLOCK_SIZE=4194304}, and
+@code{BLOCK_SIZE=4MD} is equivalent to @code{BLOCK_SIZE=4000000}.
+
+The following size letters are defined. Large sizes like @code{1Y}
+may be rejected by your computer due to limitations of its arithmetic.
+
+@table @samp
+@item k
+kilo: @math{2^10 = 1024} for @code{human-readable},
+or @math{10^3 = 1000} for @code{si}.
+@item M
+Mega: @math{2^20 = 1,048,576}
+or @math{10^6 = 1,000,000}.
+@item G
+Giga: @math{2^30 = 1,073,741,824}
+or @math{10^9 = 1,000,000,000}.
+@item T
+Tera: @math{2^40 = 1,099,511,627,776}
+or @math{10^12 = 1,000,000,000,000}.
+@item P
+Peta: @math{2^50 = 1,125,899,906,842,624}
+or @math{10^15 = 1,000,000,000,000,000}.
+@item E
+Exa: @math{2^60 = 1,152,921,504,606,846,976}@*
+or @math{10^18 = 1,000,000,000,000,000,000}.
+@item Z
+Zetta: @math{2^70 = 1,180,591,620,717,411,303,424}@*
+or @math{10^21 = 1,000,000,000,000,000,000,000}.
+@item Y
+Yotta: @math{2^80 = 1,208,925,819,614,629,174,706,176}@*
+or @math{10^24 = 1,000,000,000,000,000,000,000,000}.
+@end table
+
+@opindex -k
+@opindex --kilobytes
+@opindex -h
+@opindex --human-readable
+@opindex --si
+
+Block size defaults can be overridden by an explicit
+@samp{--block-size=@var{size}} option. The @samp{-k} or
+@samp{--kilobytes} option is equivalent to @samp{--block-size=1k}, which
+is the default unless the @env{POSIXLY_CORRECT} environment variable is
+set. The @samp{-h} or @samp{--human-readable} option is equivalent to
+@samp{--block-size=human-readable}. The @samp{--si} option is
+equivalent to @samp{--block-size=si}.
+
+@node Target directory
+@section Target directory
+
+@cindex target directory
+
+Some @sc{gnu} programs (at least @code{cp}, @code{install}, @code{ln}, and
+@code{mv}) allow you to specify the target directory via this option:
+
+@table @samp
+
+@itemx @w{@kbd{--target-directory}=@var{directory}}
+@opindex --target-directory
+@cindex target directory
+@cindex destination directory
+Specify the destination @var{directory}.
+
+The interface for most programs is that after processing options and a
+finite (possibly zero) number of fixed-position arguments, the remaining
+argument list is either expected to be empty, or is a list of items
+(usually files) that will all be handled identically. The @code{xargs}
+program is designed to work well with this convention.
+
+The commands in the @code{mv}-family are unusual in that they take
+a variable number of arguments with a special case at the @emph{end}
+(namely, the target directory). This makes it nontrivial to perform some
+operations, e.g., ``move all files from here to ../d/'', because
+@code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
+doesn't have a clean way to specify an extra final argument for each
+invocation of the subject command. (It can be done by going through a
+shell command, but that requires more human labor and brain power than
+it should.)
+
+The @w{@kbd{--target-directory}} option allows the @code{cp},
+@code{install}, @code{ln}, and @code{mv} programs to be used conveniently
+with @code{xargs}. For example, you can move the files from the
+current directory to a sibling directory, @code{d} like this:
+(However, this doesn't move files whose names begin with @samp{.}.)
+
+@smallexample
+ls |xargs mv --target-directory=../d
+@end smallexample
+
+If you use the @sc{gnu} @code{find} program, you can move @emph{all}
+files with this command:
+@example
+find . -mindepth 1 -maxdepth 1 \
+ | xargs mv --target-directory=../d
+@end example
+
+But that will fail if there are no files in the current directory
+or if any file has a name containing a newline character.
+The following example removes those limitations and requires both
+@sc{gnu} @code{find} and @sc{gnu} @code{xargs}:
+@example
+find . -mindepth 1 -maxdepth 1 -print0 \
+ | xargs --null --no-run-if-empty \
+ mv --target-directory=../d
+@end example
+
+@end table
+
+@node Trailing slashes
+@section Trailing slashes
+
+@cindex trailing slashes
+
+Some @sc{gnu} programs (at least @code{cp} and @code{mv}) allow you to
+remove any trailing slashes from each @var{source} argument before
+operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
+this behavior.
+
+This is useful when a @var{source} argument may have a trailing slash and
+specify a symbolic link to a directory. This scenario is in fact rather
+common because some shells can automatically append a trailing slash when
+performing file name completion on such symbolic links. Without this
+option, @code{mv}, for example, (via the system's rename function) must
+interpret a trailing slash as a request to dereference the symbolic link
+and so must rename the indirectly referenced @emph{directory} and not
+the symbolic link. Although it may seem surprising that such behavior
+be the default, it is required by @sc{posix.2} and is consistent with
+other parts of that standard.
+
+@node Output of entire files
+@chapter Output of entire files
+
+@cindex output of entire files
+@cindex entire files, output of
+
+These commands read and write entire files, possibly transforming them
+in some way.
+
+@menu
+* cat invocation:: Concatenate and write files.
+* tac invocation:: Concatenate and write files in reverse.
+* nl invocation:: Number lines and write files.
+* od invocation:: Write files in octal or other formats.
+@end menu
+
+@node cat invocation
+@section @code{cat}: Concatenate and write files
+
+@pindex cat
+@cindex concatenate and write files
+@cindex copying files
+
+@code{cat} copies each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output. Synopsis:
+
+@example
+cat [@var{option}] [@var{file}]@dots{}
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -A
+@itemx --show-all
+@opindex -A
+@opindex --show-all
+Equivalent to @samp{-vET}.
+
+@item -B
+@itemx --binary
+@opindex -B
+@opindex --binary
+@cindex binary and text I/O in cat
+On MS-DOS and MS-Windows only, read and write the files in binary mode.
+By default, @code{cat} on MS-DOS/MS-Windows uses binary mode only when
+standard output is redirected to a file or a pipe; this option overrides
+that. Binary file I/O is used so that the files retain their format
+(Unix text as opposed to DOS text and binary), because @code{cat} is
+frequently used as a file-copying program. Some options (see below)
+cause @code{cat} to read and write files in text mode because in those
+cases the original file contents aren't important (e.g., when lines are
+numbered by @code{cat}, or when line endings should be marked). This is
+so these options work as DOS/Windows users would expect; for example,
+DOS-style text files have their lines end with the CR-LF pair of
+characters, which won't be processed as an empty line by @samp{-b} unless
+the file is read in text mode.
+
+@item -b
+@itemx --number-nonblank
+@opindex -b
+@opindex --number-nonblank
+Number all nonblank output lines, starting with 1. On MS-DOS and
+MS-Windows, this option causes @code{cat} to read and write files in
+text mode.
+
+@item -e
+@opindex -e
+Equivalent to @samp{-vE}.
+
+@item -E
+@itemx --show-ends
+@opindex -E
+@opindex --show-ends
+Display a @samp{$} after the end of each line. On MS-DOS and
+MS-Windows, this option causes @code{cat} to read and write files in
+text mode.
+
+@item -n
+@itemx --number
+@opindex -n
+@opindex --number
+Number all output lines, starting with 1. On MS-DOS and MS-Windows,
+this option causes @code{cat} to read and write files in text mode.
+
+@item -s
+@itemx --squeeze-blank
+@opindex -s
+@opindex --squeeze-blank
+@cindex squeezing blank lines
+Replace multiple adjacent blank lines with a single blank line. On
+MS-DOS and MS-Windows, this option causes @code{cat} to read and write
+files in text mode.
+
+@item -t
+@opindex -t
+Equivalent to @samp{-vT}.
+
+@item -T
+@itemx --show-tabs
+@opindex -T
+@opindex --show-tabs
+Display TAB characters as @samp{^I}.
+
+@item -u
+@opindex -u
+Ignored; for Unix compatibility.
+
+@item -v
+@itemx --show-nonprinting
+@opindex -v
+@opindex --show-nonprinting
+Display control characters except for LFD and TAB using
+@samp{^} notation and precede characters that have the high bit set with
+@samp{M-}. On MS-DOS and MS-Windows, this option causes @code{cat} to
+read files and standard input in DOS binary mode, so the CR
+characters at the end of each line are also visible.
+
+@end table
+
+
+@node tac invocation
+@section @code{tac}: Concatenate and write files in reverse
+
+@pindex tac
+@cindex reversing files
+
+@code{tac} copies each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output, reversing the
+records (lines by default) in each separately. Synopsis:
+
+@example
+tac [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@dfn{Records} are separated by instances of a string (newline by
+default). By default, this separator string is attached to the end of
+the record that it follows in the file.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx --before
+@opindex -b
+@opindex --before
+The separator is attached to the beginning of the record that it
+precedes in the file.
+
+@item -r
+@itemx --regex
+@opindex -r
+@opindex --regex
+Treat the separator string as a regular expression. Users of @code{tac}
+on MS-DOS/MS-Windows should note that, since @code{tac} reads files in
+binary mode, each line of a text file might end with a CR/LF pair
+instead of the Unix-style LF.
+
+@item -s @var{separator}
+@itemx --separator=@var{separator}
+@opindex -s
+@opindex --separator
+Use @var{separator} as the record separator, instead of newline.
+
+@end table
+
+
+@node nl invocation
+@section @code{nl}: Number lines and write files
+
+@pindex nl
+@cindex numbering lines
+@cindex line numbering
+
+@code{nl} writes each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output, with line numbers
+added to some or all of the lines. Synopsis:
+
+@example
+nl [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@cindex logical pages, numbering on
+@code{nl} decomposes its input into (logical) pages; by default, the
+line number is reset to 1 at the top of each logical page. @code{nl}
+treats all of the input files as a single document; it does not reset
+line numbers or logical pages between files.
+
+@cindex headers, numbering
+@cindex body, numbering
+@cindex footers, numbering
+A logical page consists of three sections: header, body, and footer.
+Any of the sections can be empty. Each can be numbered in a different
+style from the others.
+
+The beginnings of the sections of logical pages are indicated in the
+input file by a line containing exactly one of these delimiter strings:
+
+@table @samp
+@item \:\:\:
+start of header;
+@item \:\:
+start of body;
+@item \:
+start of footer.
+@end table
+
+The two characters from which these strings are made can be changed from
+@samp{\} and @samp{:} via options (see below), but the pattern and
+length of each string cannot be changed.
+
+A section delimiter is replaced by an empty line on output. Any text
+that comes before the first section delimiter string in the input file
+is considered to be part of a body section, so @code{nl} treats a
+file that contains no section delimiters as a single body section.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b @var{style}
+@itemx --body-numbering=@var{style}
+@opindex -b
+@opindex --body-numbering
+Select the numbering style for lines in the body section of each
+logical page. When a line is not numbered, the current line number
+is not incremented, but the line number separator character is still
+prepended to the line. The styles are:
+
+@table @samp
+@item a
+number all lines,
+@item t
+number only nonempty lines (default for body),
+@item n
+do not number lines (default for header and footer),
+@item p@var{regexp}
+number only lines that contain a match for @var{regexp}.
+@end table
+
+@item -d @var{cd}
+@itemx --section-delimiter=@var{cd}
+@opindex -d
+@opindex --section-delimiter
+@cindex section delimiters of pages
+Set the section delimiter characters to @var{cd}; default is
+@samp{\:}. If only @var{c} is given, the second remains @samp{:}.
+(Remember to protect @samp{\} or other metacharacters from shell
+expansion with quotes or extra backslashes.)
+
+@item -f @var{style}
+@itemx --footer-numbering=@var{style}
+@opindex -f
+@opindex --footer-numbering
+Analogous to @samp{--body-numbering}.
+
+@item -h @var{style}
+@itemx --header-numbering=@var{style}
+@opindex -h
+@opindex --header-numbering
+Analogous to @samp{--body-numbering}.
+
+@item -i @var{number}
+@itemx --page-increment=@var{number}
+@opindex -i
+@opindex --page-increment
+Increment line numbers by @var{number} (default 1).
+
+@item -l @var{number}
+@itemx --join-blank-lines=@var{number}
+@opindex -l
+@opindex --join-blank-lines
+@cindex empty lines, numbering
+@cindex blank lines, numbering
+Consider @var{number} (default 1) consecutive empty lines to be one
+logical line for numbering, and only number the last one. Where fewer
+than @var{number} consecutive empty lines occur, do not number them.
+An empty line is one that contains no characters, not even spaces
+or tabs.
+
+@item -n @var{format}
+@itemx --number-format=@var{format}
+@opindex -n
+@opindex --number-format
+Select the line numbering format (default is @code{rn}):
+
+@table @samp
+@item ln
+@opindex ln @r{format for @code{nl}}
+left justified, no leading zeros;
+@item rn
+@opindex rn @r{format for @code{nl}}
+right justified, no leading zeros;
+@item rz
+@opindex rz @r{format for @code{nl}}
+right justified, leading zeros.
+@end table
+
+@item -p
+@itemx --no-renumber
+@opindex -p
+@opindex --no-renumber
+Do not reset the line number at the start of a logical page.
+
+@item -s @var{string}
+@itemx --number-separator=@var{string}
+@opindex -s
+@opindex --number-separator
+Separate the line number from the text line in the output with
+@var{string} (default is the TAB character).
+
+@item -v @var{number}
+@itemx --starting-line-number=@var{number}
+@opindex -v
+@opindex --starting-line-number
+Set the initial line number on each logical page to @var{number} (default 1).
+
+@item -w @var{number}
+@itemx --number-width=@var{number}
+@opindex -w
+@opindex --number-width
+Use @var{number} characters for line numbers (default 6).
+
+@end table
+
+
+@node od invocation
+@section @code{od}: Write files in octal or other formats
+
+@pindex od
+@cindex octal dump of files
+@cindex hex dump of files
+@cindex ASCII dump of files
+@cindex file contents, dumping unambiguously
+
+@code{od} writes an unambiguous representation of each @var{file}
+(@samp{-} means standard input), or standard input if none are given.
+Synopsis:
+
+@example
+od [@var{option}]@dots{} [@var{file}]@dots{}
+od -C [@var{file}] [[+]@var{offset} [[+]@var{label}]]
+@end example
+
+Each line of output consists of the offset in the input, followed by
+groups of data from the file. By default, @code{od} prints the offset in
+octal, and each group of file data is two bytes of input printed as a
+single octal number.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -A @var{radix}
+@itemx --address-radix=@var{radix}
+@opindex -A
+@opindex --address-radix
+@cindex radix for file offsets
+@cindex file offset radix
+Select the base in which file offsets are printed. @var{radix} can
+be one of the following:
+
+@table @samp
+@item d
+decimal;
+@item o
+octal;
+@item x
+hexadecimal;
+@item n
+none (do not print offsets).
+@end table
+
+The default is octal.
+
+@item -j @var{bytes}
+@itemx --skip-bytes=@var{bytes}
+@opindex -j
+@opindex --skip-bytes
+Skip @var{bytes} input bytes before formatting and writing. If
+@var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
+hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
+in decimal. Appending @samp{b} multiplies @var{bytes} by 512, @samp{k}
+by 1024, and @samp{m} by 1048576.
+
+@item -N @var{bytes}
+@itemx --read-bytes=@var{bytes}
+@opindex -N
+@opindex --read-bytes
+Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
+@code{bytes} are interpreted as for the @samp{-j} option.
+
+@item -s [@var{n}]
+@itemx --strings[=@var{n}]
+@opindex -s
+@opindex --strings
+@cindex string constants, outputting
+Instead of the normal output, output only @dfn{string constants}: at
+least @var{n} (3 by default) consecutive @sc{ascii} graphic characters,
+followed by a null (zero) byte.
+
+@item -t @var{type}
+@itemx --format=@var{type}
+@opindex -t
+@opindex --format
+Select the format in which to output the file data. @var{type} is a
+string of one or more of the below type indicator characters. If you
+include more than one type indicator character in a single @var{type}
+string, or use this option more than once, @code{od} writes one copy
+of each output line using each of the data types that you specified,
+in the order that you specified.
+
+Adding a trailing ``z'' to any type specification appends a display
+of the @sc{ascii} character representation of the printable characters
+to the output line generated by the type specification.
+
+@table @samp
+@item a
+named character
+@item c
+@sc{ascii} character or backslash escape,
+@item d
+signed decimal
+@item f
+floating point
+@item o
+octal
+@item u
+unsigned decimal
+@item x
+hexadecimal
+@end table
+
+The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
+newline, and @samp{nul} for a null (zero) byte. Type @code{c} outputs
+@samp{ }, @samp{\n}, and @code{\0}, respectively.
+
+@cindex type size
+Except for types @samp{a} and @samp{c}, you can specify the number
+of bytes to use in interpreting each number in the given data type
+by following the type indicator character with a decimal integer.
+Alternately, you can specify the size of one of the C compiler's
+built-in data types by following the type indicator character with
+one of the following characters. For integers (@samp{d}, @samp{o},
+@samp{u}, @samp{x}):
+
+@table @samp
+@item C
+char
+@item S
+short
+@item I
+int
+@item L
+long
+@end table
+
+For floating point (@code{f}):
+
+@table @asis
+@item F
+float
+@item D
+double
+@item L
+long double
+@end table
+
+@item -v
+@itemx --output-duplicates
+@opindex -v
+@opindex --output-duplicates
+Output consecutive lines that are identical. By default, when two or
+more consecutive output lines would be identical, @code{od} outputs only
+the first line, and puts just an asterisk on the following line to
+indicate the elision.
+
+@item -w[@var{n}]
+@itemx --width[=@var{n}]
+@opindex -w
+@opindex --width
+Dump @code{n} input bytes per output line. This must be a multiple of
+the least common multiple of the sizes associated with the specified
+output types. If @var{n} is omitted, the default is 32. If this option
+is not given at all, the default is 16.
+
+@end table
+
+The next several options map the old, pre-@sc{posix} format specification
+options to the corresponding @sc{posix} format specs.
+@sc{gnu} @code{od} accepts
+any combination of old- and new-style options. Format specification
+options accumulate.
+
+@table @samp
+
+@item -a
+@opindex -a
+Output as named characters. Equivalent to @samp{-ta}.
+
+@item -b
+@opindex -b
+Output as octal bytes. Equivalent to @samp{-toC}.
+
+@item -c
+@opindex -c
+Output as @sc{ascii} characters or backslash escapes. Equivalent to
+@samp{-tc}.
+
+@item -d
+@opindex -d
+Output as unsigned decimal shorts. Equivalent to @samp{-tu2}.
+
+@item -f
+@opindex -f
+Output as floats. Equivalent to @samp{-tfF}.
+
+@item -h
+@opindex -h
+Output as hexadecimal shorts. Equivalent to @samp{-tx2}.
+
+@item -i
+@opindex -i
+Output as decimal shorts. Equivalent to @samp{-td2}.
+
+@item -l
+@opindex -l
+Output as decimal longs. Equivalent to @samp{-td4}.
+
+@item -o
+@opindex -o
+Output as octal shorts. Equivalent to @samp{-to2}.
+
+@item -x
+@opindex -x
+Output as hexadecimal shorts. Equivalent to @samp{-tx2}.
+
+@item -C
+@itemx --traditional
+@opindex --traditional
+Recognize the pre-@sc{posix} non-option arguments that traditional @code{od}
+accepted. The following syntax:
+
+@smallexample
+od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
+@end smallexample
+
+@noindent
+can be used to specify at most one file and optional arguments
+specifying an offset and a pseudo-start address, @var{label}. By
+default, @var{offset} is interpreted as an octal number specifying how
+many input bytes to skip before formatting and writing. The optional
+trailing decimal point forces the interpretation of @var{offset} as a
+decimal number. If no decimal is specified and the offset begins with
+@samp{0x} or @samp{0X} it is interpreted as a hexadecimal number. If
+there is a trailing @samp{b}, the number of bytes skipped will be
+@var{offset} multiplied by 512. The @var{label} argument is interpreted
+just like @var{offset}, but it specifies an initial pseudo-address. The
+pseudo-addresses are displayed in parentheses following any normal
+address.
+
+@end table
+
+
+@node Formatting file contents
+@chapter Formatting file contents
+
+@cindex formatting file contents
+
+These commands reformat the contents of files.
+
+@menu
+* fmt invocation:: Reformat paragraph text.
+* pr invocation:: Paginate or columnate files for printing.
+* fold invocation:: Wrap input lines to fit in specified width.
+@end menu
+
+
+@node fmt invocation
+@section @code{fmt}: Reformat paragraph text
+
+@pindex fmt
+@cindex reformatting paragraph text
+@cindex paragraphs, reformatting
+@cindex text, reformatting
+
+@code{fmt} fills and joins lines to produce output lines of (at most)
+a given number of characters (75 by default). Synopsis:
+
+@example
+fmt [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@code{fmt} reads from the specified @var{file} arguments (or standard
+input if none are given), and writes to standard output.
+
+By default, blank lines, spaces between words, and indentation are
+preserved in the output; successive input lines with different
+indentation are not joined; tabs are expanded on input and introduced on
+output.
+
+@cindex line-breaking
+@cindex sentences and line-breaking
+@cindex Knuth, Donald E.
+@cindex Plass, Michael F.
+@code{fmt} prefers breaking lines at the end of a sentence, and tries to
+avoid line breaks after the first word of a sentence or before the last
+word of a sentence. A @dfn{sentence break} is defined as either the end
+of a paragraph or a word ending in any of @samp{.?!}, followed by two
+spaces or end of line, ignoring any intervening parentheses or quotes.
+Like @TeX{}, @code{fmt} reads entire ``paragraphs'' before choosing line
+breaks; the algorithm is a variant of that in ``Breaking Paragraphs Into
+Lines'' (Donald E. Knuth and Michael F. Plass, @cite{Software---Practice
+and Experience}, 11 (1981), 1119--1184).
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --crown-margin
+@opindex -c
+@opindex --crown-margin
+@cindex crown margin
+@dfn{Crown margin} mode: preserve the indentation of the first two
+lines within a paragraph, and align the left margin of each subsequent
+line with that of the second line.
+
+@item -t
+@itemx --tagged-paragraph
+@opindex -t
+@opindex --tagged-paragraph
+@cindex tagged paragraphs
+@dfn{Tagged paragraph} mode: like crown margin mode, except that if
+indentation of the first line of a paragraph is the same as the
+indentation of the second, the first line is treated as a one-line
+paragraph.
+
+@item -s
+@itemx --split-only
+@opindex -s
+@opindex --split-only
+Split lines only. Do not join short lines to form longer ones. This
+prevents sample lines of code, and other such ``formatted'' text from
+being unduly combined.
+
+@item -u
+@itemx --uniform-spacing
+@opindex -u
+@opindex --uniform-spacing
+Uniform spacing. Reduce spacing between words to one space, and spacing
+between sentences to two spaces.
+
+@item -@var{width}
+@itemx -w @var{width}
+@itemx --width=@var{width}
+@opindex -@var{width}
+@opindex -w
+@opindex --width
+Fill output lines up to @var{width} characters (default 75). @code{fmt}
+initially tries to make lines about 7% shorter than this, to give it
+room to balance line lengths.
+
+@item -p @var{prefix}
+@itemx --prefix=@var{prefix}
+Only lines beginning with @var{prefix} (possibly preceded by whitespace)
+are subject to formatting. The prefix and any preceding whitespace are
+stripped for the formatting and then re-attached to each formatted output
+line. One use is to format certain kinds of program comments, while
+leaving the code unchanged.
+
+@end table
+
+
+@node pr invocation
+@section @code{pr}: Paginate or columnate files for printing
+
+@pindex pr
+@cindex printing, preparing files for
+@cindex multicolumn output, generating
+@cindex merging files in parallel
+
+@code{pr} writes each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output, paginating and
+optionally outputting in multicolumn format; optionally merges all
+@var{file}s, printing all in parallel, one per column. Synopsis:
+
+@example
+pr [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@vindex LC_MESSAGES
+By default, a 5-line header is printed at each page: two blank lines;
+a line with the date, the filename, and the page count; and two more
+blank lines. A footer of five blank lines is also printed. With the @samp{-F}
+option, a 3-line header is printed: the leading two blank lines are
+omitted; no footer is used. The default @var{page_length} in both cases is 66
+lines. The default number of text lines changes from 56 (without @samp{-F})
+to 63 (with @samp{-F}). The text line of the header takes the form
+@samp{@var{date} @var{string} @var{page}}, with spaces inserted around
+@var{string} so that the line takes up the full @var{page_width}. Here,
+@var{date} is the date (see the @option{-D} or @option{--date-format}
+option for details), @var{string} is the centered header string, and
+@var{page} identifies the page number. The @env{LC_MESSAGES} locale
+category affects the spelling of @var{page}; in the default C locale, it
+is @samp{Page @var{number}} where @var{number} is the decimal page
+number.
+
+Form feeds in the input cause page breaks in the output. Multiple form
+feeds produce empty pages.
+
+Columns are of equal width, separated by an optional string (default
+is @samp{space}). For multicolumn output, lines will always be truncated to
+@var{page_width} (default 72), unless you use the @samp{-J} option. For single
+column output no line truncation occurs by default. Use @samp{-W} option to
+truncate lines in that case.
+
+The following changes were made in version 1.22i and apply to later
+versions of @command{pr}:
+@c FIXME: this whole section here sounds very awkward to me. I
+@c made a few small changes, but really it all needs to be redone. - Brian
+@c OK, I fixed another sentence or two, but some of it I just don't understand.
+@ - Brian
+@itemize @bullet
+
+@item
+Some small @var{letter options} (@samp{-s}, @samp{-w}) have been
+redefined for better @sc{posix} compliance. The output of some further
+cases has been adapted to other Unix systems. These changes are not
+compatible with earlier versions of the program.
+
+@item
+Some @var{new capital letter} options (@samp{-J}, @samp{-S}, @samp{-W})
+have been introduced to turn off unexpected interferences of small letter
+options. The @samp{-N} option and the second argument @var{last_page}
+of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
+form feeds set in the input files requires the @samp{-T} option.
+
+@item
+Capital letter options override small letter ones.
+
+@item
+Some of the option-arguments (compare @samp{-s}, @samp{-S}, @samp{-e},
+@samp{-i}, @samp{-n}) cannot be specified as separate arguments from the
+preceding option letter (already stated in the @sc{posix} specification).
+@end itemize
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item +@var{first_page}[:@var{last_page}]
+@itemx --pages=@var{first_page}[:@var{last_page}]
+@opindex +@var{first_page}[:@var{last_page}]
+@opindex --pages
+Begin printing with page @var{first_page} and stop with @var{last_page}.
+Missing @samp{:@var{last_page}} implies end of file. While estimating
+the number of skipped pages each form feed in the input file results
+in a new page. Page counting with and without @samp{+@var{first_page}}
+is identical. By default, counting starts with the first page of input
+file (not first page printed). Line numbering may be altered by @samp{-N}
+option.
+
+@item -@var{column}
+@itemx --columns=@var{column}
+@opindex -@var{column}
+@opindex --columns
+@cindex down columns
+With each single @var{file}, produce @var{column} columns of output
+(default is 1) and print columns down, unless @samp{-a} is used. The
+column width is automatically decreased as @var{column} increases; unless
+you use the @samp{-W/-w} option to increase @var{page_width} as well.
+This option might well cause some lines to be truncated. The number of
+lines in the columns on each page are balanced. The options @samp{-e}
+and @samp{-i} are on for multiple text-column output. Together with
+@samp{-J} option column alignment and line truncation is turned off.
+Lines of full length are joined in a free field format and @samp{-S}
+option may set field separators. @samp{-@var{column}} may not be used
+with @samp{-m} option.
+
+@item -a
+@itemx --across
+@opindex -a
+@opindex --across
+@cindex across columns
+With each single @var{file}, print columns across rather than down. The
+@samp{-@var{column}} option must be given with @var{column} greater than one.
+If a line is too long to fit in a column, it is truncated.
+
+@item -c
+@itemx --show-control-chars
+@opindex -c
+@opindex --show-control-chars
+Print control characters using hat notation (e.g., @samp{^G}); print
+other nonprinting characters in octal backslash notation. By default,
+nonprinting characters are not changed.
+
+@item -d
+@itemx --double-space
+@opindex -d
+@opindex --double-space
+@cindex double spacing
+Double space the output.
+
+@item -D @var{format}
+@itemx --date-format=@var{format}
+@cindex time formats
+@cindex formatting times
+Format header dates using @var{format}, using the same conventions as
+for the the command @samp{date +@var{format}}; @xref{date invocation, ,
+,sh-utils,GNU shell utilities}. Except for directives, which start with
+@samp{%}, characters in @var{format} are printed unchanged. You can use
+this option to specify an arbitrary string in place of the header date,
+e.g., @samp{--date-format="Monday morning"}.
+
+@vindex POSIXLY_CORRECT
+@vindex LC_TIME
+If the @env{POSIXLY_CORRECT} environment variable is not set, the date
+format defaults to @samp{%Y-%m-%d %H:%M} (for example, @samp{2001-12-04
+23:59}); otherwise, the format depends on the @env{LC_TIME} locale
+category, with the default being @samp{%b %e %H:%M %Y} (for example,
+@samp{Dec@ @ 4 23:59 2001}.
+
+@item -e[@var{in-tabchar}[@var{in-tabwidth}]]
+@itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
+@opindex -e
+@opindex --expand-tabs
+@cindex input tabs
+Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
+the input tab character (default is the TAB character). Second optional
+argument @var{in-tabwidth} is the input tab character's width (default
+is 8).
+
+@item -f
+@itemx -F
+@itemx --form-feed
+@opindex -F
+@opindex -f
+@opindex --form-feed
+Use a form feed instead of newlines to separate output pages. The default
+page length of 66 lines is not altered. But the number of lines of text
+per page changes from default 56 to 63 lines.
+
+@item -h @var{HEADER}
+@itemx --header=@var{HEADER}
+@opindex -h
+@opindex --header
+Replace the filename in the header with the centered string @var{header}.
+When using the shell, @var{header} should be quoted and should be
+separated from @option{-h} by a space.
+
+@item -i[@var{out-tabchar}[@var{out-tabwidth}]]
+@itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
+@opindex -i
+@opindex --output-tabs
+@cindex output tabs
+Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
+is the output tab character (default is the TAB character). Second optional
+argument @var{out-tabwidth} is the output tab character's width (default
+is 8).
+
+@item -J
+@itemx --join-lines
+@opindex -J
+@opindex --join-lines
+Merge lines of full length. Used together with the column options
+@samp{-@var{column}}, @samp{-a -@var{column}} or @samp{-m}. Turns off
+@samp{-W/-w} line truncation;
+no column alignment used; may be used with @samp{-S[@var{string}]}.
+@samp{-J} has been introduced (together with @samp{-W} and @samp{-S})
+to disentangle the old (@sc{posix}-compliant) options @samp{-w} and
+@samp{-s} along with the three column options.
+
+
+@item -l @var{page_length}
+@itemx --length=@var{page_length}
+@opindex -l
+@opindex --length
+Set the page length to @var{page_length} (default 66) lines, including
+the lines of the header [and the footer]. If @var{page_length} is less
+than or equal to 10 (or <= 3 with @samp{-F}), the header and footer are
+omitted, and all form feeds set in input files are eliminated, as if
+the @samp{-T} option had been given.
+
+@item -m
+@itemx --merge
+@opindex -m
+@opindex --merge
+Merge and print all @var{file}s in parallel, one in each column. If a
+line is too long to fit in a column, it is truncated, unless the @samp{-J}
+option is used. @samp{-S[@var{string}]} may be used. Empty pages in
+some @var{file}s (form feeds set) produce empty columns, still marked
+by @var{string}. The result is a continuous line numbering and column
+marking throughout the whole merged file. Completely empty merged pages
+show no separators or line numbers. The default header becomes
+@samp{@var{date} @var{page}} with spaces inserted in the middle; this
+may be used with the @option{-h} or @option{--header} option to fill up
+the middle blank part.
+
+@item -n[@var{number-separator}[@var{digits}]]
+@itemx --number-lines[=@var{number-separator}[@var{digits}]]
+@opindex -n
+@opindex --number-lines
+Provide @var{digits} digit line numbering (default for @var{digits} is
+5). With multicolumn output the number occupies the first @var{digits}
+column positions of each text column or only each line of @samp{-m}
+output. With single column output the number precedes each line just as
+@samp{-m} does. Default counting of the line numbers starts with the
+first line of the input file (not the first line printed, compare the
+@samp{--page} option and @samp{-N} option).
+Optional argument @var{number-separator} is the character appended to
+the line number to separate it from the text followed. The default
+separator is the TAB character. In a strict sense a TAB is always
+printed with single column output only. The @var{TAB}-width varies
+with the @var{TAB}-position, e.g. with the left @var{margin} specified
+by @samp{-o} option. With multicolumn output priority is given to
+@samp{equal width of output columns} (a @sc{posix} specification).
+The @var{TAB}-width is fixed to the value of the first column and does
+not change with different values of left @var{margin}. That means a
+fixed number of spaces is always printed in the place of the
+@var{number-separator tab}. The tabification depends upon the output
+position.
+
+@item -N @var{line_number}
+@itemx --first-line-number=@var{line_number}
+@opindex -N
+@opindex --first-line-number
+Start line counting with the number @var{line_number} at first line of
+first page printed (in most cases not the first line of the input file).
+
+@item -o @var{margin}
+@itemx --indent=@var{margin}
+@opindex -o
+@opindex --indent
+@cindex indenting lines
+@cindex left margin
+Indent each line with a margin @var{margin} spaces wide (default is zero).
+The total page width is the size of the margin plus the @var{page_width}
+set with the @samp{-W/-w} option. A limited overflow may occur with
+numbered single column output (compare @samp{-n} option).
+
+@item -r
+@itemx --no-file-warnings
+@opindex -r
+@opindex --no-file-warnings
+Do not print a warning message when an argument @var{file} cannot be
+opened. (The exit status will still be nonzero, however.)
+
+@item -s[@var{char}]
+@itemx --separator[=@var{char}]
+@opindex -s
+@opindex --separator
+Separate columns by a single character @var{char}. The default for
+@var{char} is the TAB character without @samp{-w} and @samp{no
+character} with @samp{-w}. Without @samp{-s} the default separator
+@samp{space} is set. @samp{-s[char]} turns off line truncation of all
+three column options (@samp{-COLUMN}|@samp{-a -COLUMN}|@samp{-m}) unless
+@samp{-w} is set. This is a @sc{posix}-compliant formulation.
+
+
+@item -S[@var{string}]
+@itemx --sep-string[=@var{string}]
+@opindex -S
+@opindex --sep-string
+Use @var{string} to separate output columns. The @samp{-S} option doesn't
+affect the @samp{-W/-w} option, unlike the @samp{-s} option which does. It
+does not affect line truncation or column alignment.
+Without @samp{-S}, and with @samp{-J}, @code{pr} uses the default output
+separator, TAB.
+Without @samp{-S} or @samp{-J}, @code{pr} uses a @samp{space}
+(same as @samp{-S" "}).
+Using @samp{-S} with no @var{string} is equivalent to @samp{-S""}.
+Note that for some of @code{pr}'s options the single-letter option
+character must be followed immediately by any corresponding argument;
+there may not be any intervening white space.
+@samp{-S/-s} is one of them. Don't use @samp{-S "STRING"}.
+@sc{posix} requires this.
+
+@item -t
+@itemx --omit-header
+@opindex -t
+@opindex --omit-header
+Do not print the usual header [and footer] on each page, and do not fill
+out the bottom of pages (with blank lines or a form feed). No page
+structure is produced, but form feeds set in the input files are retained.
+The predefined pagination is not changed. @samp{-t} or @samp{-T} may be
+useful together with other options; e.g.: @samp{-t -e4}, expand TAB characters
+in the input file to 4 spaces but don't make any other changes. Use of
+@samp{-t} overrides @samp{-h}.
+
+@item -T
+@itemx --omit-pagination
+@opindex -T
+@opindex --omit-pagination
+Do not print header [and footer]. In addition eliminate all form feeds
+set in the input files.
+
+@item -v
+@itemx --show-nonprinting
+@opindex -v
+@opindex --show-nonprinting
+Print nonprinting characters in octal backslash notation.
+
+@item -w @var{page_width}
+@itemx --width=@var{page_width}
+@opindex -w
+@opindex --width
+Set page width to @var{page_width} characters for multiple text-column
+output only (default for @var{page_width} is 72). @samp{-s[CHAR]} turns
+off the default page width and any line truncation and column alignment.
+Lines of full length are merged, regardless of the column options
+set. No @var{page_width} setting is possible with single column output.
+A @sc{posix}-compliant formulation.
+
+@item -W @var{page_width}
+@itemx --page_width=@var{page_width}
+@opindex -W
+@opindex --page_width
+Set the page width to @var{page_width} characters. That's valid with and
+without a column option. Text lines are truncated, unless @samp{-J}
+is used. Together with one of the three column options
+(@samp{-@var{column}}, @samp{-a -@var{column}} or @samp{-m}) column
+alignment is always used. The separator options @samp{-S} or @samp{-s}
+don't affect the @samp{-W} option. Default is 72 characters. Without
+@samp{-W @var{page_width}} and without any of the column options NO line
+truncation is used (defined to keep downward compatibility and to meet
+most frequent tasks). That's equivalent to @samp{-W 72 -J}. The header
+line is never truncated.
+
+@end table
+
+
+@node fold invocation
+@section @code{fold}: Wrap input lines to fit in specified width
+
+@pindex fold
+@cindex wrapping long input lines
+@cindex folding long input lines
+
+@code{fold} writes each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output, breaking long
+lines. Synopsis:
+
+@example
+fold [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+By default, @code{fold} breaks lines wider than 80 columns. The output
+is split into as many lines as necessary.
+
+@cindex screen columns
+@code{fold} counts screen columns by default; thus, a tab may count more
+than one column, backspace decreases the column count, and carriage
+return sets the column to zero.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx --bytes
+@opindex -b
+@opindex --bytes
+Count bytes rather than columns, so that tabs, backspaces, and carriage
+returns are each counted as taking up one column, just like other
+characters.
+
+@item -s
+@itemx --spaces
+@opindex -s
+@opindex --spaces
+Break at word boundaries: the line is broken after the last blank before
+the maximum line length. If the line contains no such blanks, the line
+is broken at the maximum line length as usual.
+
+@item -w @var{width}
+@itemx --width=@var{width}
+@opindex -w
+@opindex --width
+Use a maximum line length of @var{width} columns instead of 80.
+
+@end table
+
+
+@node Output of parts of files
+@chapter Output of parts of files
+
+@cindex output of parts of files
+@cindex parts of files, output of
+
+These commands output pieces of the input.
+
+@menu
+* head invocation:: Output the first part of files.
+* tail invocation:: Output the last part of files.
+* split invocation:: Split a file into fixed-size pieces.
+* csplit invocation:: Split a file into context-determined pieces.
+@end menu
+
+@node head invocation
+@section @code{head}: Output the first part of files
+
+@pindex head
+@cindex initial part of files, outputting
+@cindex first part of files, outputting
+
+@code{head} prints the first part (10 lines by default) of each
+@var{file}; it reads from standard input if no files are given or
+when given a @var{file} of @samp{-}. Synopses:
+
+@example
+head [@var{option}]@dots{} [@var{file}]@dots{}
+head -@var{number} [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+If more than one @var{file} is specified, @code{head} prints a
+one-line header consisting of
+@example
+==> @var{file name} <==
+@end example
+@noindent
+before the output for each @var{file}.
+
+@code{head} accepts two option formats: the new one, in which numbers
+are arguments to the options (@samp{-q -n 1}), and the old one, in which
+the number precedes any option letters (@samp{-1q}).
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -@var{count}@var{options}
+@opindex -@var{count}
+This option is only recognized if it is specified first. @var{count} is
+a decimal number optionally followed by a size letter (@samp{b},
+@samp{k}, @samp{m}) as in @code{-c}, or @samp{l} to mean count by lines,
+or other option letters (@samp{cqv}).
+
+@item -c @var{bytes}
+@itemx --bytes=@var{bytes}
+@opindex -c
+@opindex --bytes
+Print the first @var{bytes} bytes, instead of initial lines. Appending
+@samp{b} multiplies @var{bytes} by 512, @samp{k} by 1024, and @samp{m}
+by 1048576.
+
+@itemx -n @var{n}
+@itemx --lines=@var{n}
+@opindex -n
+@opindex --lines
+Output the first @var{n} lines.
+
+@item -q
+@itemx --quiet
+@itemx --silent
+@opindex -q
+@opindex --quiet
+@opindex --silent
+Never print file name headers.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Always print file name headers.
+
+@end table
+
+
+@node tail invocation
+@section @code{tail}: Output the last part of files
+
+@pindex tail
+@cindex last part of files, outputting
+
+@code{tail} prints the last part (10 lines by default) of each
+@var{file}; it reads from standard input if no files are given or
+when given a @var{file} of @samp{-}. Synopses:
+
+@example
+tail [@var{option}]@dots{} [@var{file}]@dots{}
+tail -@var{number} [@var{option}]@dots{} [@var{file}]@dots{}
+tail +@var{number} [@var{option}]@dots{} [@var{file}]@dots{} # obsolescent
+@end example
+
+If more than one @var{file} is specified, @code{tail} prints a
+one-line header consisting of
+@example
+==> @var{file name} <==
+@end example
+@noindent
+before the output for each @var{file}.
+
+@cindex BSD @code{tail}
+@sc{gnu} @code{tail} can output any amount of data (some other versions of
+@code{tail} cannot). It also has no @samp{-r} option (print in
+reverse), since reversing a file is really a different job from printing
+the end of a file; BSD @code{tail} (which is the one with @code{-r}) can
+only reverse files that are at most as large as its buffer, which is
+typically 32k. A more reliable and versatile way to reverse files is
+the @sc{gnu} @code{tac} command.
+
+@code{tail} accepts two option formats: the new one, in which numbers
+are arguments to the options (@samp{-n 1}), and the obsolescent one, in
+which the number precedes any option letters (@samp{-1} or @samp{+1}).
+Warning: support for the @samp{+1} form will be withdrawn, as future
+versions of @sc{posix} will not allow it.
+
+If any option-argument is a number @var{n} starting with a @samp{+},
+@code{tail} begins printing with the @var{n}th item from the start of
+each file, instead of from the end.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -@var{count}
+@itemx +@var{count}
+@opindex -@var{count}
+@opindex +@var{count}
+This option is only recognized if it is specified first. @var{count} is
+a decimal number optionally followed by a size letter (@samp{b},
+@samp{k}, @samp{m}) as in @code{-c}, or @samp{l} to mean count by lines,
+or other option letters (@samp{cfqv}).
+
+Warning: the @samp{+@var{count}} usage is obsolescent. Future versions
+of @sc{posix} will require that support for it be withdrawn. Use
+@samp{-n +@var{count}} instead.
+
+@item -c @var{bytes}
+@itemx --bytes=@var{bytes}
+@opindex -c
+@opindex --bytes
+Output the last @var{bytes} bytes, instead of final lines. Appending
+@samp{b} multiplies @var{bytes} by 512, @samp{k} by 1024, and @samp{m}
+by 1048576.
+
+@item -f
+@itemx --follow[=@var{how}]
+@opindex -f
+@opindex --follow
+@cindex growing files
+@vindex name @r{follow option}
+@vindex descriptor @r{follow option}
+Loop forever trying to read more characters at the end of the file,
+presumably because the file is growing. This option is ignored when
+reading from a pipe.
+If more than one file is given, @code{tail} prints a header whenever it
+gets output from a different file, to indicate which file that output is
+from.
+
+There are two ways to specify how you'd like to track files with this option,
+but that difference is noticeable only when a followed file is removed or
+renamed.
+If you'd like to continue to track the end of a growing file even after
+it has been unlinked, use @samp{--follow=descriptor}. This is the default
+behavior, but it is not useful if you're tracking a log file that may be
+rotated (removed or renamed, then reopened). In that case, use
+@samp{--follow=name} to track the named file by reopening it periodically
+to see if it has been removed and recreated by some other program.
+
+No matter which method you use, if the tracked file is determined to have
+shrunk, @code{tail} prints a message saying the file has been truncated
+and resumes tracking the end of the file from the newly-determined endpoint.
+
+When a file is removed, @code{tail}'s behavior depends on whether it is
+following the name or the descriptor. When following by name, tail can
+detect that a file has been removed and gives a message to that effect,
+and if @samp{--retry} has been specified it will continue checking
+periodically to see if the file reappears.
+When following a descriptor, tail does not detect that the file has
+been unlinked or renamed and issues no message; even though the file
+may no longer be accessible via its original name, it may still be
+growing.
+
+The option values @samp{descriptor} and @samp{name} may be specified only
+with the long form of the option, not with @samp{-f}.
+
+@itemx --retry
+@opindex --retry
+This option is meaningful only when following by name.
+Without this option, when tail encounters a file that doesn't
+exist or is otherwise inaccessible, it reports that fact and
+never checks it again.
+
+@itemx --sleep-interval=@var{n}
+@opindex --sleep-interval
+Change the number of seconds to wait between iterations (the default is 1).
+During one iteration, every specified file is checked to see if it has
+changed size.
+
+@itemx --pid=@var{pid}
+@opindex --pid
+When following by name or by descriptor, you may specify the process ID,
+@var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
+after that process terminates, tail will also terminate. This will
+work properly only if the writer and the tailing process are running on
+the same machine. For example, to save the output of a build in a file
+and to watch the file grow, if you invoke @code{make} and @code{tail}
+like this then the tail process will stop when your build completes.
+Without this option, you would have had to kill the @code{tail -f}
+process yourself.
+@example
+$ make >& makerr & tail --pid=$! -f makerr
+@end example
+If you specify a @var{pid} that is not in use or that does not correspond
+to the process that is writing to the tailed files, then @code{tail}
+may terminate long before any @var{file}s stop growing or it may not
+terminate until long after the real writer has terminated.
+Note that @samp{--pid} cannot be supported on some systems; @code{tail}
+will print a warning if this is the case.
+
+@itemx --max-unchanged-stats=@var{n}
+@opindex --max-unchanged-stats
+When tailing a file by name, if there have been @var{n} (default
+n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
+iterations for which the size has remained the same, then
+@code{open}/@code{fstat} the file to determine if that file name is
+still associated with the same device/inode-number pair as before.
+When following a log file that is rotated, this is approximately the
+number of seconds between when tail prints the last pre-rotation lines
+and when it prints the lines that have accumulated in the new log file.
+This option is meaningful only when following by name.
+
+@itemx -n @var{n}
+@itemx --lines=@var{n}
+@opindex -n
+@opindex --lines
+Output the last @var{n} lines.
+
+@item -q
+@itemx -quiet
+@itemx --silent
+@opindex -q
+@opindex --quiet
+@opindex --silent
+Never print file name headers.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Always print file name headers.
+
+@end table
+
+
+@node split invocation
+@section @code{split}: Split a file into fixed-size pieces
+
+@pindex split
+@cindex splitting a file into pieces
+@cindex pieces, splitting a file into
+
+@code{split} creates output files containing consecutive sections of
+@var{input} (standard input if none is given or @var{input} is
+@samp{-}). Synopsis:
+
+@example
+split [@var{option}] [@var{input} [@var{prefix}]]
+@end example
+
+By default, @code{split} puts 1000 lines of @var{input} (or whatever is
+left over for the last section), into each output file.
+
+@cindex output file name prefix
+The output files' names consist of @var{prefix} (@samp{x} by default)
+followed by a group of letters @samp{aa}, @samp{ab}, and so on, such
+that concatenating the output files in sorted order by file name produces
+the original input file. (If more than 676 output files are required,
+@code{split} uses @samp{zaa}, @samp{zab}, etc.)
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -@var{lines}
+@itemx -l @var{lines}
+@itemx --lines=@var{lines}
+@opindex -l
+@opindex --lines
+Put @var{lines} lines of @var{input} into each output file.
+
+@item -b @var{bytes}
+@itemx --bytes=@var{bytes}
+@opindex -b
+@opindex --bytes
+Put the first @var{bytes} bytes of @var{input} into each output file.
+Appending @samp{b} multiplies @var{bytes} by 512, @samp{k} by 1024, and
+@samp{m} by 1048576.
+
+@item -C @var{bytes}
+@itemx --line-bytes=@var{bytes}
+@opindex -C
+@opindex --line-bytes
+Put into each output file as many complete lines of @var{input} as
+possible without exceeding @var{bytes} bytes. For lines longer than
+@var{bytes} bytes, put @var{bytes} bytes into each output file until
+less than @var{bytes} bytes of the line are left, then continue
+normally. @var{bytes} has the same format as for the @samp{--bytes}
+option.
+
+@itemx --verbose
+@opindex --verbose
+Write a diagnostic to standard error just before each output file is opened.
+
+@end table
+
+
+@node csplit invocation
+@section @code{csplit}: Split a file into context-determined pieces
+
+@pindex csplit
+@cindex context splitting
+@cindex splitting a file into pieces by context
+
+@code{csplit} creates zero or more output files containing sections of
+@var{input} (standard input if @var{input} is @samp{-}). Synopsis:
+
+@example
+csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
+@end example
+
+The contents of the output files are determined by the @var{pattern}
+arguments, as detailed below. An error occurs if a @var{pattern}
+argument refers to a nonexistent line of the input file (e.g., if no
+remaining line matches a given regular expression). After every
+@var{pattern} has been matched, any remaining input is copied into one
+last output file.
+
+By default, @code{csplit} prints the number of bytes written to each
+output file after it has been created.
+
+The types of pattern arguments are:
+
+@table @samp
+
+@item @var{n}
+Create an output file containing the input up to but not including line
+@var{n} (a positive integer). If followed by a repeat count, also
+create an output file containing the next @var{line} lines of the input
+file once for each repeat.
+
+@item /@var{regexp}/[@var{offset}]
+Create an output file containing the current line up to (but not
+including) the next line of the input file that contains a match for
+@var{regexp}. The optional @var{offset} is a @samp{+} or @samp{-}
+followed by a positive integer. If it is given, the input up to the
+matching line plus or minus @var{offset} is put into the output file,
+and the line after that begins the next section of input.
+
+@item %@var{regexp}%[@var{offset}]
+Like the previous type, except that it does not create an output
+file, so that section of the input file is effectively ignored.
+
+@item @{@var{repeat-count}@}
+Repeat the previous pattern @var{repeat-count} additional
+times. @var{repeat-count} can either be a positive integer or an
+asterisk, meaning repeat as many times as necessary until the input is
+exhausted.
+
+@end table
+
+The output files' names consist of a prefix (@samp{xx} by default)
+followed by a suffix. By default, the suffix is an ascending sequence
+of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
+concatenating the output files in sorted order by filename produces the
+original input file.
+
+By default, if @code{csplit} encounters an error or receives a hangup,
+interrupt, quit, or terminate signal, it removes any output files
+that it has created so far before it exits.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -f @var{prefix}
+@itemx --prefix=@var{prefix}
+@opindex -f
+@opindex --prefix
+@cindex output file name prefix
+Use @var{prefix} as the output file name prefix.
+
+@item -b @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -b
+@opindex --suffix
+@cindex output file name suffix
+Use @var{suffix} as the output file name suffix. When this option is
+specified, the suffix string must include exactly one
+@code{printf(3)}-style conversion specification, possibly including
+format specification flags, a field width, a precision specifications,
+or all of these kinds of modifiers. The format letter must convert a
+binary integer argument to readable form; thus, only @samp{d}, @samp{i},
+@samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
+entire @var{suffix} is given (with the current output file number) to
+@code{sprintf(3)} to form the file name suffixes for each of the
+individual output files in turn. If this option is used, the
+@samp{--digits} option is ignored.
+
+@item -n @var{digits}
+@itemx --digits=@var{digits}
+@opindex -n
+@opindex --digits
+Use output file names containing numbers that are @var{digits} digits
+long instead of the default 2.
+
+@item -k
+@itemx --keep-files
+@opindex -k
+@opindex --keep-files
+Do not remove output files when errors are encountered.
+
+@item -z
+@itemx --elide-empty-files
+@opindex -z
+@opindex --elide-empty-files
+Suppress the generation of zero-length output files. (In cases where
+the section delimiters of the input file are supposed to mark the first
+lines of each of the sections, the first output file will generally be a
+zero-length file unless you use this option.) The output file sequence
+numbers always run consecutively starting from 0, even when this option
+is specified.
+
+@item -s
+@itemx -q
+@itemx --silent
+@itemx --quiet
+@opindex -s
+@opindex -q
+@opindex --silent
+@opindex --quiet
+Do not print counts of output file sizes.
+
+@end table
+
+
+@node Summarizing files
+@chapter Summarizing files
+
+@cindex summarizing files
+
+These commands generate just a few numbers representing entire
+contents of files.
+
+@menu
+* wc invocation:: Print byte, word, and line counts.
+* sum invocation:: Print checksum and block counts.
+* cksum invocation:: Print CRC checksum and byte counts.
+* md5sum invocation:: Print or check message-digests.
+@end menu
+
+
+@node wc invocation
+@section @code{wc}: Print byte, word, and line counts
+
+@pindex wc
+@cindex byte count
+@cindex character count
+@cindex word count
+@cindex line count
+
+@code{wc} counts the number of bytes, characters, whitespace-separated
+words, and newlines in each given @var{file}, or standard input if none
+are given or for a @var{file} of @samp{-}. Synopsis:
+
+@example
+wc [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@cindex total counts
+@vindex POSIXLY_CORRECT
+@code{wc} prints one line of counts for each file, and if the file was
+given as an argument, it prints the file name following the counts. If
+more than one @var{file} is given, @code{wc} prints a final line
+containing the cumulative counts, with the file name @file{total}. The
+counts are printed in this order: newlines, words, characters, bytes.
+By default, each count is output right-justified in a 7-byte field with
+one space between fields so that the numbers and file names line up nicely
+in columns. However, @sc{posix} requires that there be exactly one space
+separating columns. You can make @code{wc} use the @sc{posix}-mandated
+output format by setting the @env{POSIXLY_CORRECT} environment variable.
+
+By default, @code{wc} prints three counts: the newline, words, and byte
+counts. Options can specify that only certain counts be printed.
+Options do not undo others previously given, so
+
+@example
+wc --bytes --words
+@end example
+
+@noindent
+prints both the byte counts and the word counts.
+
+With the @code{--max-line-length} option, @code{wc} prints the length
+of the longest line per file, and if there is more than one file it
+prints the maximum (not the sum) of those lengths.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --bytes
+@opindex -c
+@opindex --bytes
+Print only the byte counts.
+
+@item -m
+@itemx --chars
+@opindex -m
+@opindex --chars
+Print only the character counts.
+
+@item -w
+@itemx --words
+@opindex -w
+@opindex --words
+Print only the word counts.
+
+@item -l
+@itemx --lines
+@opindex -l
+@opindex --lines
+Print only the newline counts.
+
+@item -L
+@itemx --max-line-length
+@opindex -L
+@opindex --max-line-length
+Print only the maximum line lengths.
+
+@end table
+
+
+@node sum invocation
+@section @code{sum}: Print checksum and block counts
+
+@pindex sum
+@cindex 16-bit checksum
+@cindex checksum, 16-bit
+
+@code{sum} computes a 16-bit checksum for each given @var{file}, or
+standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
+
+@example
+sum [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@code{sum} prints the checksum for each @var{file} followed by the
+number of blocks in the file (rounded up). If more than one @var{file}
+is given, file names are also printed (by default). (With the
+@samp{--sysv} option, corresponding file names are printed when there is
+at least one file argument.)
+
+By default, @sc{gnu} @code{sum} computes checksums using an algorithm
+compatible with BSD @code{sum} and prints file sizes in units of
+1024-byte blocks.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -r
+@opindex -r
+@cindex BSD @code{sum}
+Use the default (BSD compatible) algorithm. This option is included for
+compatibility with the System V @code{sum}. Unless @samp{-s} was also
+given, it has no effect.
+
+@item -s
+@itemx --sysv
+@opindex -s
+@opindex --sysv
+@cindex System V @code{sum}
+Compute checksums using an algorithm compatible with System V
+@code{sum}'s default, and print file sizes in units of 512-byte blocks.
+
+@end table
+
+@code{sum} is provided for compatibility; the @code{cksum} program (see
+next section) is preferable in new applications.
+
+
+@node cksum invocation
+@section @code{cksum}: Print CRC checksum and byte counts
+
+@pindex cksum
+@cindex cyclic redundancy check
+@cindex CRC checksum
+
+@code{cksum} computes a cyclic redundancy check (CRC) checksum for each
+given @var{file}, or standard input if none are given or for a
+@var{file} of @samp{-}. Synopsis:
+
+@example
+cksum [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@code{cksum} prints the CRC checksum for each file along with the number
+of bytes in the file, and the filename unless no arguments were given.
+
+@code{cksum} is typically used to ensure that files
+transferred by unreliable means (e.g., netnews) have not been corrupted,
+by comparing the @code{cksum} output for the received files with the
+@code{cksum} output for the original files (typically given in the
+distribution).
+
+The CRC algorithm is specified by the @sc{posix.2} standard. It is not
+compatible with the BSD or System V @code{sum} algorithms (see the
+previous section); it is more robust.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node md5sum invocation
+@section @code{md5sum}: Print or check message-digests
+
+@pindex md5sum
+@cindex 128-bit checksum
+@cindex checksum, 128-bit
+@cindex fingerprint, 128-bit
+@cindex message-digest, 128-bit
+
+@code{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
+@dfn{message-digest}) for each specified @var{file}.
+If a @var{file} is specified as @samp{-} or if no files are given
+@code{md5sum} computes the checksum for the standard input.
+@code{md5sum} can also determine whether a file and checksum are
+consistent. Synopses:
+
+@example
+md5sum [@var{option}]@dots{} [@var{file}]@dots{}
+md5sum [@var{option}]@dots{} --check [@var{file}]
+@end example
+
+For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
+indicating a binary or text input file, and the filename.
+If @var{file} is omitted or specified as @samp{-}, standard input is read.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx --binary
+@opindex -b
+@opindex --binary
+@cindex binary input files
+Treat all input files as binary. This option has no effect on Unix
+systems, since they don't distinguish between binary and text files.
+This option is useful on systems that have different internal and
+external character representations. On MS-DOS and MS-Windows, this is
+the default.
+
+@item -c
+@itemx --check
+Read filenames and checksum information from the single @var{file}
+(or from stdin if no @var{file} was specified) and report whether
+each named file and the corresponding checksum data are consistent.
+The input to this mode of @code{md5sum} is usually the output of
+a prior, checksum-generating run of @samp{md5sum}.
+Each valid line of input consists of an MD5 checksum, a binary/text
+flag, and then a filename.
+Binary files are marked with @samp{*}, text with @samp{ }.
+For each such line, @code{md5sum} reads the named file and computes its
+MD5 checksum. Then, if the computed message digest does not match the
+one on the line with the filename, the file is noted as having
+failed the test. Otherwise, the file passes the test.
+By default, for each valid line, one line is written to standard
+output indicating whether the named file passed the test.
+After all checks have been performed, if there were any failures,
+a warning is issued to standard error.
+Use the @samp{--status} option to inhibit that output.
+If any listed file cannot be opened or read, if any valid line has
+an MD5 checksum inconsistent with the associated file, or if no valid
+line is found, @code{md5sum} exits with nonzero status. Otherwise,
+it exits successfully.
+
+@itemx --status
+@opindex --status
+@cindex verifying MD5 checksums
+This option is useful only when verifying checksums.
+When verifying checksums, don't generate the default one-line-per-file
+diagnostic and don't output the warning summarizing any failures.
+Failures to open or read a file still evoke individual diagnostics to
+standard error.
+If all listed files are readable and are consistent with the associated
+MD5 checksums, exit successfully. Otherwise exit with a status code
+indicating there was a failure.
+
+@item -t
+@itemx --text
+@opindex -t
+@opindex --text
+@cindex text input files
+Treat all input files as text files. This is the reverse of
+@samp{--binary}.
+
+@item -w
+@itemx --warn
+@opindex -w
+@opindex --warn
+@cindex verifying MD5 checksums
+When verifying checksums, warn about improperly formatted MD5 checksum lines.
+This option is useful only if all but a few lines in the checked input
+are valid.
+
+@end table
+
+
+@node Operating on sorted files
+@chapter Operating on sorted files
+
+@cindex operating on sorted files
+@cindex sorted files, operations on
+
+These commands work with (or produce) sorted files.
+
+@menu
+* sort invocation:: Sort text files.
+* uniq invocation:: Uniquify files.
+* comm invocation:: Compare two sorted files line by line.
+* ptx invocation:: Produce a permuted index of file contents.
+* tsort invocation:: Topological sort.
+@end menu
+
+
+@node sort invocation
+@section @code{sort}: Sort text files
+
+@pindex sort
+@cindex sorting files
+
+@code{sort} sorts, merges, or compares all the lines from the given
+files, or standard input if none are given or for a @var{file} of
+@samp{-}. By default, @code{sort} writes the results to standard
+output. Synopsis:
+
+@example
+sort [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@code{sort} has three modes of operation: sort (the default), merge,
+and check for sortedness. The following options change the operation
+mode:
+
+@table @samp
+
+@item -c
+@itemx --check
+@opindex -c
+@opindex --check
+@cindex checking for sortedness
+Check whether the given files are already sorted: if they are not all
+sorted, print an error message and exit with a status of 1.
+Otherwise, exit successfully.
+
+@item -m
+@itemx --merge
+@opindex -m
+@opindex --merge
+@cindex merging sorted files
+Merge the given files by sorting them as a group. Each input file must
+always be individually sorted. It always works to sort instead of
+merge; merging is provided because it is faster, in the case where it
+works.
+
+@end table
+
+@vindex LC_COLLATE
+A pair of lines is compared as follows: if any key fields have been
+specified, @code{sort} compares each pair of fields, in the order
+specified on the command line, according to the associated ordering
+options, until a difference is found or no fields are left.
+Unless otherwise specified, all comparisons use the character
+collating sequence specified by the @env{LC_COLLATE} locale.
+
+If any of the global options @samp{bdfgiMnr} are given but no key fields
+are specified, @code{sort} compares the entire lines according to the
+global options.
+
+Finally, as a last resort when all keys compare equal (or if no ordering
+options were specified at all), @code{sort} compares the entire lines.
+The last resort comparison honors the @option{--reverse} (@option{-r})
+global option. The @option{--stable} (@option{-s}) option disables this
+last-resort comparison so that lines in which all fields compare equal
+are left in their original relative order. If no fields or global
+options are specified, @option{--stable} (@option{-s}) has no effect.
+
+@sc{gnu} @code{sort} (as specified for all @sc{gnu} utilities) has no limits on
+input line length or restrictions on bytes allowed within lines. In
+addition, if the final byte of an input file is not a newline, @sc{gnu}
+@code{sort} silently supplies one. A line's trailing newline is not
+part of the line for comparison purposes.@footnote{@sc{posix}.2-1992
+requires that the trailing newline be part of the comparison, and some
+@code{sort} implementations obey this requirement, but it is widely
+considered to be a bug in the standard and the next version of
+@sc{posix}.2 will likely remove this requirement.}
+
+Upon any error, @code{sort} exits with a status of @samp{2}.
+
+@vindex TMPDIR
+If the environment variable @env{TMPDIR} is set, @code{sort} uses its
+value as the directory for temporary files instead of @file{/tmp}. The
+@option{--temporary-directory} (@option{-T}) option in turn overrides
+the environment variable.
+
+
+The following options affect the ordering of output lines. They may be
+specified globally or as part of a specific key field. If no key
+fields are specified, global options apply to comparison of entire
+lines; otherwise the global options are inherited by key fields that do
+not specify any special options of their own. In pre-@sc{posix}
+versions of @command{sort}, global options affect only later key fields,
+so portable shell scripts should specify global options first.
+
+@table @samp
+
+@item -b
+@itemx --ignore-leading-blanks
+@opindex -b
+@opindex --ignore-leading-blanks
+@cindex blanks, ignoring leading
+@vindex LC_CTYPE
+Ignore leading blanks when finding sort keys in each line.
+The @env{LC_CTYPE} locale determines character types.
+
+@item -d
+@itemx --dictionary-order
+@opindex -d
+@opindex --dictionary-order
+@cindex dictionary order
+@cindex phone directory order
+@cindex telephone directory order
+@vindex LC_CTYPE
+Sort in @dfn{phone directory} order: ignore all characters except
+letters, digits and blanks when sorting.
+The @env{LC_CTYPE} locale determines character types.
+
+@item -f
+@itemx --ignore-case
+@opindex -f
+@opindex --ignore-case
+@cindex ignoring case
+@cindex case folding
+@vindex LC_CTYPE
+Fold lowercase characters into the equivalent uppercase characters when
+comparing so that, for example, @samp{b} and @samp{B} sort as equal.
+The @env{LC_CTYPE} locale determines character types.
+
+@item -g
+@itemx --general-numeric-sort
+@opindex -g
+@opindex --general-numeric-sort
+@cindex general numeric sort
+@vindex LC_NUMERIC
+Sort numerically, using the standard C function @code{strtod} to convert
+a prefix of each line to a double-precision floating point number.
+This allows floating point numbers to be specified in scientific notation,
+like @code{1.0e-34} and @code{10e100}.
+The @env{LC_NUMERIC} locale determines the decimal-point character.
+Do not report overflow, underflow, or conversion errors.
+Use the following collating sequence:
+
+@itemize @bullet
+@item
+Lines that do not start with numbers (all considered to be equal).
+@item
+NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
+in a consistent but machine-dependent order.
+@item
+Minus infinity.
+@item
+Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
+@item
+Plus infinity.
+@end itemize
+
+Use this option only if there is no alternative; it is much slower than
+@option{--numeric-sort} (@option{-n}) and it can lose information when
+converting to floating point.
+
+@item -i
+@itemx --ignore-nonprinting
+@opindex -i
+@opindex --ignore-nonprinting
+@cindex nonprinting characters, ignoring
+@cindex unprintable characters, ignoring
+@vindex LC_CTYPE
+Ignore nonprinting characters.
+The @env{LC_CTYPE} locale determines character types.
+
+@item -M
+@itemx --month-sort
+@opindex -M
+@opindex --month-sort
+@cindex months, sorting by
+@vindex LC_TIME
+An initial string, consisting of any amount of whitespace, followed
+by a month name abbreviation, is folded to UPPER case and
+compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
+Invalid names compare low to valid names. The @env{LC_TIME} locale
+determines the month spellings.
+
+@item -n
+@itemx --numeric-sort
+@opindex -n
+@opindex --numeric-sort
+@cindex numeric sort
+@vindex LC_NUMERIC
+Sort numerically: the number begins each line; specifically, it consists
+of optional whitespace, an optional @samp{-} sign, and zero or more
+digits possibly separated by thousands separators, optionally followed
+by a decimal-point character and zero or more digits. The @env{LC_NUMERIC}
+locale specifies the decimal-point character and thousands separator.
+
+Numeric sort uses what might be considered an unconventional method to
+compare strings representing floating point numbers. Rather than first
+converting each string to the C @code{double} type and then comparing
+those values, @command{sort} aligns the decimal-point characters in the
+two strings and compares the strings a character at a time. One benefit
+of using this approach is its speed. In practice this is much more
+efficient than performing the two corresponding string-to-double (or
+even string-to-integer) conversions and then comparing doubles. In
+addition, there is no corresponding loss of precision. Converting each
+string to @code{double} before comparison would limit precision to about
+16 digits on most systems.
+
+Neither a leading @samp{+} nor exponential notation is recognized.
+To compare such strings numerically, use the
+@option{--general-numeric-sort} (@option{-g}) option.
+
+@item -r
+@itemx --reverse
+@opindex -r
+@opindex --reverse
+@cindex reverse sorting
+Reverse the result of comparison, so that lines with greater key values
+appear earlier in the output instead of later.
+
+@end table
+
+Other options are:
+
+@table @samp
+
+@item -o @var{output-file}
+@itemx --output=@var{output-file}
+@opindex -o
+@opindex --output
+@cindex overwriting of input, allowed
+Write output to @var{output-file} instead of standard output.
+If necessary, @command{sort} reads input before opening
+@var{output-file}, so you can safely sort a file in place by using
+commands like @code{sort -o F F} and @code{cat F | sort -o F}.
+
+@vindex POSIXLY_CORRECT
+If @option{-c} is not also specified, @option{-o} may appear after an
+input file even if @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o
+F}. Warning: this usage is obsolescent. Future versions of @sc{posix}
+will require that support for it be withdrawn. Portable scripts should
+specify @samp{-o @var{output-file}} before any input files.
+
+@item -S @var{size}
+@itemx --buffer-size=@var{size}
+@opindex -S
+@opindex --buffer-size
+@cindex size for main memory sorting
+Use a main-memory sort buffer of the given @var{size}. By default,
+@var{size} is in units of 1,024 bytes. Appending @samp{%} causes
+@var{size} to be interpreted as a percentage of physical memory.
+Appending @samp{k} multiplies @var{size} by 1,024 (the default),
+@samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
+@samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
+@samp{b} causes @var{size} to be interpreted as a byte count, with no
+multiplication.
+
+This option can improve the performance of @command{sort} by causing it
+to start with a larger or smaller sort buffer than the default.
+However, this option affects only the initial buffer size. The buffer
+grows beyond @var{size} if @command{sort} encounters input lines larger
+than @var{size}.
+
+@item -t @var{separator}
+@itemx --field-separator=@var{separator}
+@opindex -t
+@opindex --field-separator
+@cindex field separator character
+Use character @var{separator} as the field separator when finding the
+sort keys in each line. By default, fields are separated by the empty
+string between a non-whitespace character and a whitespace character.
+That is, given the input line @w{@samp{ foo bar}}, @code{sort} breaks it
+into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
+not considered to be part of either the field preceding or the field
+following. But note that sort fields that extend to the end of the line,
+as @samp{-k 2}, or sort fields consisting of a range, as @samp{-k 2,3},
+retain the field separators present between the endpoints of the range.
+
+@item -T @var{tempdir}
+@itemx --temporary-directory=@var{tempdir}
+@opindex -T
+@opindex --temporary-directory
+@cindex temporary directory
+@vindex TMPDIR
+Use directory @var{tempdir} to store temporary files, overriding the
+@env{TMPDIR} environment variable. If this option is given more than
+once, temporary files are stored in all the directories given. If you
+have a large sort or merge that is I/O-bound, you can often improve
+performance by using this option to specify directories on different
+disks and controllers.
+
+@item -u
+@itemx --unique
+@opindex -u
+@opindex --unique
+@cindex uniquifying output
+
+Normally, output only the first of a sequence of lines that compare
+equal. For the @option{--check} (@option{-c}) option,
+check that no pair of consecutive lines compares equal.
+
+@item -k @var{pos1}[,@var{pos2}]
+@itemx --key=@var{pos1}[,@var{pos2}]
+@opindex -k
+@opindex --key
+@cindex sort field
+Specify a sort field that consists of the part of the line between
+@var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
+omitted), @emph{inclusive}. Fields and character positions are numbered
+starting with 1. So to sort on the second field, you'd use
+@samp{--key=2,2} (@samp{-k 2,2}). See below for more examples.
+
+@item -z
+@itemx --zero-terminated
+@opindex -z
+@opindex --zero-terminated
+@cindex sort zero-terminated lines
+Treat the input as a set of lines, each terminated by a zero byte (@sc{ascii}
+@sc{nul} (Null) character) instead of an @sc{ascii} @sc{lf} (Line Feed).
+This option can be useful in conjunction with @samp{perl -0} or
+@samp{find -print0} and @samp{xargs -0} which do the same in order to
+reliably handle arbitrary pathnames (even those which contain Line Feed
+characters.)
+
+@item +@var{pos1} [-@var{pos2}]
+The obsolescent, traditional option for specifying a sort field. The field
+consists of the line between @var{pos1} and up to but @emph{not including}
+@var{pos2} (or the end of the line if @var{pos2} is omitted). Fields
+and character positions are numbered starting with 0. See below.
+
+Warning: the @samp{+@var{pos1}} usage is obsolescent. Future versions of
+@sc{posix} will require that support for it be withdrawn. Use
+@option{--key} (@option{-k}) instead.
+
+@end table
+
+Historical (BSD and System V) implementations of @code{sort} have
+differed in their interpretation of some options, particularly
+@samp{-b}, @samp{-f}, and @samp{-n}. @sc{gnu} sort follows the @sc{posix}
+behavior, which is usually (but not always!) like the System V behavior.
+According to @sc{posix}, @samp{-n} no longer implies @samp{-b}. For
+consistency, @samp{-M} has been changed in the same way. This may
+affect the meaning of character positions in field specifications in
+obscure cases. The only fix is to add an explicit @samp{-b}.
+
+A position in a sort field specified with the @samp{-k} or @samp{+}
+option has the form @samp{@var{f}.@var{c}}, where @var{f} is the number
+of the field to use and @var{c} is the number of the first character
+from the beginning of the field (for @samp{+@var{pos}}) or from the end
+of the previous field (for @samp{-@var{pos}}). If the @samp{.@var{c}}
+is omitted, it is taken to be the first character in the field. If the
+@samp{-b} option was specified, the @samp{.@var{c}} part of a field
+specification is counted from the first nonblank character of the field
+(for @samp{+@var{pos}}) or from the first nonblank character following
+the previous field (for @samp{-@var{pos}}).
+
+A sort key option may also have any of the option letters @samp{Mbdfinr}
+appended to it, in which case the global ordering options are not used
+for that particular field. The @samp{-b} option may be independently
+attached to either or both of the @samp{+@var{pos}} and
+@samp{-@var{pos}} parts of a field specification, and if it is inherited
+from the global options it will be attached to both.
+Keys may span multiple fields.
+
+Here are some examples to illustrate various combinations of options.
+In them, the @sc{posix} @samp{-k} option is used to specify sort keys rather
+than the obsolescent @samp{+@var{pos1}-@var{pos2}} syntax.
+
+@itemize @bullet
+
+@item
+Sort in descending (reverse) numeric order.
+
+@example
+sort -nr
+@end example
+
+@item
+Sort alphabetically, omitting the first and second fields.
+This uses a single key composed of the characters beginning
+at the start of field three and extending to the end of each line.
+
+@example
+sort -k 3
+@end example
+
+@item
+Sort numerically on the second field and resolve ties by sorting
+alphabetically on the third and fourth characters of field five.
+Use @samp{:} as the field delimiter.
+
+@example
+sort -t : -k 2,2n -k 5.3,5.4
+@end example
+
+Note that if you had written @samp{-k 2} instead of @samp{-k 2,2}
+@command{sort} would have used all characters beginning in the second field
+and extending to the end of the line as the primary @emph{numeric}
+key. For the large majority of applications, treating keys spanning
+more than one field as numeric will not do what you expect.
+
+Also note that the @samp{n} modifier was applied to the field-end
+specifier for the first key. It would have been equivalent to
+specify @samp{-k 2n,2} or @samp{-k 2n,2n}. All modifiers except
+@samp{b} apply to the associated @emph{field}, regardless of whether
+the modifier character is attached to the field-start and/or the
+field-end part of the key specifier.
+
+@item
+Sort the password file on the fifth field and ignore any
+leading white space. Sort lines with equal values in field five
+on the numeric user ID in field three.
+
+@example
+sort -t : -k 5b,5 -k 3,3n /etc/passwd
+@end example
+
+An alternative is to use the global numeric modifier @samp{-n}.
+
+@example
+sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
+@end example
+
+@item
+Generate a tags file in case-insensitive sorted order.
+
+@smallexample
+find src -type f -print0 | sort -t / -z -f | xargs -0 etags --append
+@end smallexample
+
+The use of @samp{-print0}, @samp{-z}, and @samp{-0} in this case means
+that pathnames that contain Line Feed characters will not get broken up
+by the sort operation.
+
+Finally, to ignore both leading and trailing white space, you
+could have applied the @samp{b} modifier to the field-end specifier
+for the first key,
+
+@example
+sort -t : -n -k 5b,5b -k 3,3 /etc/passwd
+@end example
+
+or by using the global @samp{-b} modifier instead of @samp{-n}
+and an explicit @samp{n} with the second key specifier.
+
+@example
+sort -t : -b -k 5,5 -k 3,3n /etc/passwd
+@end example
+
+@c This example is a bit contrived and needs more explanation.
+@c @item
+@c Sort records separated by an arbitrary string by using a pipe to convert
+@c each record delimiter string to @samp{\0}, then using sort's -z option,
+@c and converting each @samp{\0} back to the original record delimiter.
+@c
+@c @example
+@c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
+@c @end example
+
+@end itemize
+
+
+@node uniq invocation
+@section @code{uniq}: Uniquify files
+
+@pindex uniq
+@cindex uniquify files
+
+@code{uniq} writes the unique lines in the given @file{input}, or
+standard input if nothing is given or for an @var{input} name of
+@samp{-}. Synopsis:
+
+@example
+uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
+@end example
+
+By default, @code{uniq} prints the unique lines in a sorted file, i.e.,
+discards all but one of identical successive lines. Optionally, it can
+instead show only lines that appear exactly once, or lines that appear
+more than once.
+
+The input must be sorted. If your input is not sorted, perhaps you want
+to use @code{sort -u}.
+
+If no @var{output} file is specified, @code{uniq} writes to standard
+output.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -@var{n}
+@itemx -f @var{n}
+@itemx --skip-fields=@var{n}
+@opindex -@var{n}
+@opindex -f
+@opindex --skip-fields
+Skip @var{n} fields on each line before checking for uniqueness. Fields
+are sequences of non-space non-tab characters that are separated from
+each other by at least one space or tab.
+
+@item +@var{n}
+@itemx -s @var{n}
+@itemx --skip-chars=@var{n}
+@opindex +@var{n}
+@opindex -s
+@opindex --skip-chars
+Skip @var{n} characters before checking for uniqueness. If you use both
+the field and character skipping options, fields are skipped over first.
+
+Warning: the @samp{+@var{n}} usage is obsolescent. Future versions of
+@sc{posix} will require that support for it be withdrawn. Use @samp{-s
+@var{n}} instead.
+
+@item -c
+@itemx --count
+@opindex -c
+@opindex --count
+Print the number of times each line occurred along with the line.
+
+@item -i
+@itemx --ignore-case
+@opindex -i
+@opindex --ignore-case
+Ignore differences in case when comparing lines.
+
+@item -d
+@itemx --repeated
+@opindex -d
+@opindex --repeated
+@cindex duplicate lines, outputting
+Print only duplicate lines.
+
+@item -D
+@itemx --all-repeated[=@var{delimit-method}]
+@opindex -D
+@opindex --all-repeated
+@cindex all duplicate lines, outputting
+Print all duplicate lines and only duplicate lines.
+This option is useful mainly in conjunction with other options e.g.,
+to ignore case or to compare only selected fields.
+The optional @var{delimit-method} tells how to delimit
+groups of duplicate lines, and must be one of the following:
+
+@table @samp
+
+@item none
+Do not delimit groups of duplicate lines.
+This is equivalent to @option{--all-repeated} (@option{-D}).
+
+@item prepend
+Output a newline before each group of duplicate lines.
+
+@item separate
+Separate groups of duplicate lines with a single newline.
+This is the same as using @samp{prepend}, except that
+there is no newline before the first group, and hence
+may be better suited for output direct to users.
+@end table
+
+Note that when groups are delimited and the input stream contains
+two or more consecutive blank lines, then the output is ambiguous.
+To avoid that, filter the input through @samp{tr -s '\n'} to replace
+each sequence of consecutive newlines with a single newline.
+
+This is a @sc{gnu} extension.
+@c FIXME: give an example showing *how* it's useful
+
+@item -u
+@itemx --unique
+@opindex -u
+@opindex --unique
+@cindex unique lines, outputting
+Print only unique lines.
+
+@item -w @var{n}
+@itemx --check-chars=@var{n}
+@opindex -w
+@opindex --check-chars
+Compare @var{n} characters on each line (after skipping any specified
+fields and characters). By default the entire rest of the lines are
+compared.
+
+@end table
+
+
+@node comm invocation
+@section @code{comm}: Compare two sorted files line by line
+
+@pindex comm
+@cindex line-by-line comparison
+@cindex comparing sorted files
+
+@code{comm} writes to standard output lines that are common, and lines
+that are unique, to two input files; a file name of @samp{-} means
+standard input. Synopsis:
+
+@example
+comm [@var{option}]@dots{} @var{file1} @var{file2}
+@end example
+
+@vindex LC_COLLATE
+Before @code{comm} can be used, the input files must be sorted using the
+collating sequence specified by the @env{LC_COLLATE} locale.
+If an input file ends in a non-newline
+character, a newline is silently appended. The @code{sort} command with
+no options always outputs a file that is suitable input to @code{comm}.
+
+@cindex differing lines
+@cindex common lines
+With no options, @code{comm} produces three column output. Column one
+contains lines unique to @var{file1}, column two contains lines unique
+to @var{file2}, and column three contains lines common to both files.
+Columns are separated by a single TAB character.
+@c FIXME: when there's an option to supply an alternative separator
+@c string, append `by default' to the above sentence.
+
+@opindex -1
+@opindex -2
+@opindex -3
+The options @samp{-1}, @samp{-2}, and @samp{-3} suppress printing of
+the corresponding columns. Also see @ref{Common options}.
+
+Unlike some other comparison utilities, @code{comm} has an exit
+status that does not depend on the result of the comparison.
+Upon normal completion @code{comm} produces an exit code of zero.
+If there is an error it exits with nonzero status.
+
+
+@node tsort invocation
+@section @code{tsort}: Topological sort
+
+@pindex tsort
+@cindex topological sort
+
+@code{tsort} performs a topological sort on the given @var{file}, or
+standard input if no input file is given or for a @var{file} of
+@samp{-}. Synopsis:
+
+@example
+tsort [@var{option}] [@var{file}]
+@end example
+
+@code{tsort} reads its input as pairs of strings, separated by blanks,
+indicating a partial ordering. The output is a total ordering that
+corresponds to the given partial ordering.
+
+For example
+
+@example
+tsort <<EOF
+a b c
+d
+e f
+b c d e
+EOF
+@end example
+
+@noindent
+will produce the output
+
+@example
+a
+b
+c
+d
+e
+f
+@end example
+
+@code{tsort} will detect cycles in the input and writes the first cycle
+encountered to standard error.
+
+Note that for a given partial ordering, generally there is no unique
+total ordering.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node ptx invocation
+@section @code{ptx}: Produce permuted indexes
+
+@pindex ptx
+
+@code{ptx} reads a text file and essentially produces a permuted index, with
+each keyword in its context. The calling sketch is either one of:
+
+@example
+ptx [@var{option} @dots{}] [@var{file} @dots{}]
+ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
+@end example
+
+The @samp{-G} (or its equivalent: @samp{--traditional}) option disables
+all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
+limitations and changing several of the program's default option values.
+When @samp{-G} is not specified, @sc{gnu} extensions are always enabled.
+@sc{gnu} extensions to @code{ptx} are documented wherever appropriate in this
+document. For the full list, see @xref{Compatibility in ptx}.
+
+Individual options are explained in the following sections.
+
+When @sc{gnu} extensions are enabled, there may be zero, one or several
+@var{file}s after the options. If there is no @var{file}, the program
+reads the standard input. If there is one or several @var{file}s, they
+give the name of input files which are all read in turn, as if all the
+input files were concatenated. However, there is a full contextual
+break between each file and, when automatic referencing is requested,
+file names and line numbers refer to individual text input files. In
+all cases, the program outputs the permuted index to the standard
+output.
+
+When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
+operates in traditional mode, there may be zero, one or two parameters
+besides the options. If there are no parameters, the program reads the
+standard input and outputs the permuted index to the standard output.
+If there is only one parameter, it names the text @var{input} to be read
+instead of the standard input. If two parameters are given, they give
+respectively the name of the @var{input} file to read and the name of
+the @var{output} file to produce. @emph{Be very careful} to note that,
+in this case, the contents of file given by the second parameter is
+destroyed. This behavior is dictated by System V @code{ptx}
+compatibility; @sc{gnu} Standards normally discourage output parameters not
+introduced by an option.
+
+Note that for @emph{any} file named as the value of an option or as an
+input text file, a single dash @kbd{-} may be used, in which case
+standard input is assumed. However, it would not make sense to use this
+convention more than once per program invocation.
+
+@menu
+* General options in ptx:: Options which affect general program behavior.
+* Charset selection in ptx:: Underlying character set considerations.
+* Input processing in ptx:: Input fields, contexts, and keyword selection.
+* Output formatting in ptx:: Types of output format, and sizing the fields.
+* Compatibility in ptx::
+@end menu
+
+
+@node General options in ptx
+@subsection General options
+
+@table @samp
+
+@item -C
+@itemx --copyright
+Print a short note about the copyright and copying conditions, then
+exit without further processing.
+
+@item -G
+@itemx --traditional
+As already explained, this option disables all @sc{gnu} extensions to
+@code{ptx} and switches to traditional mode.
+
+@item --help
+Print a short help on standard output, then exit without further
+processing.
+
+@item --version
+Print the program version on standard output, then exit without further
+processing.
+
+@end table
+
+
+@node Charset selection in ptx
+@subsection Charset selection
+
+@c FIXME: People don't necessarily know what an IBM-PC was these days.
+As it is set up now, the program assumes that the input file is coded
+using 8-bit ISO 8859-1 code, also known as Latin-1 character set,
+@emph{unless} it is compiled for MS-DOS, in which case it uses the
+character set of the IBM-PC. (@sc{gnu} @code{ptx} is not known to work on
+smaller MS-DOS machines anymore.) Compared to 7-bit @sc{ascii}, the set
+of characters which are letters is different; this alters the behavior
+of regular expression matching. Thus, the default regular expression
+for a keyword allows foreign or diacriticized letters. Keyword sorting,
+however, is still crude; it obeys the underlying character set ordering
+quite blindly.
+
+@table @samp
+
+@item -f
+@itemx --ignore-case
+Fold lower case letters to upper case for sorting.
+
+@end table
+
+
+@node Input processing in ptx
+@subsection Word selection and input processing
+
+@table @samp
+
+@item -b @var{file}
+@item --break-file=@var{file}
+
+This option provides an alternative (to @samp{-W}) method of describing
+which characters make up words. It introduces the name of a
+file which contains a list of characters which can@emph{not} be part of
+one word; this file is called the @dfn{Break file}. Any character which
+is not part of the Break file is a word constituent. If both options
+@samp{-b} and @samp{-W} are specified, then @samp{-W} has precedence and
+@samp{-b} is ignored.
+
+When @sc{gnu} extensions are enabled, the only way to avoid newline as a
+break character is to write all the break characters in the file with no
+newline at all, not even at the end of the file. When @sc{gnu} extensions
+are disabled, spaces, tabs and newlines are always considered as break
+characters even if not included in the Break file.
+
+@item -i @var{file}
+@itemx --ignore-file=@var{file}
+
+The file associated with this option contains a list of words which will
+never be taken as keywords in concordance output. It is called the
+@dfn{Ignore file}. The file contains exactly one word in each line; the
+end of line separation of words is not subject to the value of the
+@samp{-S} option.
+
+There is a default Ignore file used by @code{ptx} when this option is
+not specified, usually found in @file{/usr/local/lib/eign} if this has
+not been changed at installation time. If you want to deactivate the
+default Ignore file, specify @code{/dev/null} instead.
+
+@item -o @var{file}
+@itemx --only-file=@var{file}
+
+The file associated with this option contains a list of words which will
+be retained in concordance output; any word not mentioned in this file
+is ignored. The file is called the @dfn{Only file}. The file contains
+exactly one word in each line; the end of line separation of words is
+not subject to the value of the @samp{-S} option.
+
+There is no default for the Only file. When both an Only file and an
+Ignore file are specified, a word is considered a keyword only
+if it is listed in the Only file and not in the Ignore file.
+
+@item -r
+@itemx --references
+
+On each input line, the leading sequence of non-white space characters will be
+taken to be a reference that has the purpose of identifying this input
+line in the resulting permuted index. For more information about reference
+production, see @xref{Output formatting in ptx}.
+Using this option changes the default value for option @samp{-S}.
+
+Using this option, the program does not try very hard to remove
+references from contexts in output, but it succeeds in doing so
+@emph{when} the context ends exactly at the newline. If option
+@samp{-r} is used with @samp{-S} default value, or when @sc{gnu} extensions
+are disabled, this condition is always met and references are completely
+excluded from the output contexts.
+
+@item -S @var{regexp}
+@itemx --sentence-regexp=@var{regexp}
+
+This option selects which regular expression will describe the end of a
+line or the end of a sentence. In fact, this regular expression is not
+the only distinction between end of lines or end of sentences, and input
+line boundaries have no special significance outside this option. By
+default, when @sc{gnu} extensions are enabled and if @samp{-r} option is not
+used, end of sentences are used. In this case, this @var{regex} is
+imported from @sc{gnu} Emacs:
+
+@example
+[.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
+@end example
+
+Whenever @sc{gnu} extensions are disabled or if @samp{-r} option is used, end
+of lines are used; in this case, the default @var{regexp} is just:
+
+@example
+\n
+@end example
+
+Using an empty @var{regexp} is equivalent to completely disabling end of
+line or end of sentence recognition. In this case, the whole file is
+considered to be a single big line or sentence. The user might want to
+disallow all truncation flag generation as well, through option @samp{-F
+""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
+Manual}.
+
+When the keywords happen to be near the beginning of the input line or
+sentence, this often creates an unused area at the beginning of the
+output context line; when the keywords happen to be near the end of the
+input line or sentence, this often creates an unused area at the end of
+the output context line. The program tries to fill those unused areas
+by wrapping around context in them; the tail of the input line or
+sentence is used to fill the unused area on the left of the output line;
+the head of the input line or sentence is used to fill the unused area
+on the right of the output line.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences from the C language are recognized and converted to the
+corresponding characters by @code{ptx} itself.
+
+@item -W @var{regexp}
+@itemx --word-regexp=@var{regexp}
+
+This option selects which regular expression will describe each keyword.
+By default, if @sc{gnu} extensions are enabled, a word is a sequence of
+letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
+disabled, a word is by default anything which ends with a space, a tab
+or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
+
+An empty @var{regexp} is equivalent to not using this option.
+@xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
+Manual}.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences, as found in the C language, are recognized and converted to
+the corresponding characters by @code{ptx} itself.
+
+@end table
+
+
+@node Output formatting in ptx
+@subsection Output formatting
+
+Output format is mainly controlled by the @samp{-O} and @samp{-T} options
+described in the table below. When neither @samp{-O} nor @samp{-T} are
+selected, and if @sc{gnu} extensions are enabled, the program chooses an
+output format suitable for a dumb terminal. Each keyword occurrence is
+output to the center of one line, surrounded by its left and right
+contexts. Each field is properly justified, so the concordance output
+can be readily observed. As a special feature, if automatic
+references are selected by option @samp{-A} and are output before the
+left context, that is, if option @samp{-R} is @emph{not} selected, then
+a colon is added after the reference; this nicely interfaces with @sc{gnu}
+Emacs @code{next-error} processing. In this default output format, each
+white space character, like newline and tab, is merely changed to
+exactly one space, with no special attempt to compress consecutive
+spaces. This might change in the future. Except for those white space
+characters, every other character of the underlying set of 256
+characters is transmitted verbatim.
+
+Output format is further controlled by the following options.
+
+@table @samp
+
+@item -g @var{number}
+@itemx --gap-size=@var{number}
+
+Select the size of the minimum white space gap between the fields on the
+output line.
+
+@item -w @var{number}
+@itemx --width=@var{number}
+
+Select the maximum output width of each final line. If references are
+used, they are included or excluded from the maximum output width
+depending on the value of option @samp{-R}. If this option is not
+selected, that is, when references are output before the left context,
+the maximum output width takes into account the maximum length of all
+references. If this option is selected, that is, when references are
+output after the right context, the maximum output width does not take
+into account the space taken by references, nor the gap that precedes
+them.
+
+@item -A
+@itemx --auto-reference
+
+Select automatic references. Each input line will have an automatic
+reference made up of the file name and the line ordinal, with a single
+colon between them. However, the file name will be empty when standard
+input is being read. If both @samp{-A} and @samp{-r} are selected, then
+the input reference is still read and skipped, but the automatic
+reference is used at output time, overriding the input reference.
+
+@item -R
+@itemx --right-side-refs
+
+In the default output format, when option @samp{-R} is not used, any
+references produced by the effect of options @samp{-r} or @samp{-A} are
+placed to the far right of output lines, after the right context. With
+default output format, when the @samp{-R} option is specified, references
+are rather placed at the beginning of each output line, before the left
+context. For any other output format, option @samp{-R} is
+ignored, with one exception: with @samp{-R} the width of references
+is @emph{not} taken into account in total output width given by @samp{-w}.
+
+This option is automatically selected whenever @sc{gnu} extensions are
+disabled.
+
+@item -F @var{string}
+@itemx --flac-truncation=@var{string}
+
+This option will request that any truncation in the output be reported
+using the string @var{string}. Most output fields theoretically extend
+towards the beginning or the end of the current line, or current
+sentence, as selected with option @samp{-S}. But there is a maximum
+allowed output line width, changeable through option @samp{-w}, which is
+further divided into space for various output fields. When a field has
+to be truncated because it cannot extend beyond the beginning or the end of
+the current line to fit in, then a truncation occurs. By default,
+the string used is a single slash, as in @samp{-F /}.
+
+@var{string} may have more than one character, as in @samp{-F ...}.
+Also, in the particular case when @var{string} is empty (@samp{-F ""}),
+truncation flagging is disabled, and no truncation marks are appended in
+this case.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences, as found in the C language, are recognized and converted to
+the corresponding characters by @code{ptx} itself.
+
+@item -M @var{string}
+@itemx --macro-name=@var{string}
+
+Select another @var{string} to be used instead of @samp{xx}, while
+generating output suitable for @code{nroff}, @code{troff} or @TeX{}.
+
+@item -O
+@itemx --format=roff
+
+Choose an output format suitable for @code{nroff} or @code{troff}
+processing. Each output line will look like:
+
+@smallexample
+.xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
+@end smallexample
+
+so it will be possible to write a @samp{.xx} roff macro to take care of
+the output typesetting. This is the default output format when @sc{gnu}
+extensions are disabled. Option @samp{-M} can be used to change
+@samp{xx} to another macro name.
+
+In this output format, each non-graphical character, like newline and
+tab, is merely changed to exactly one space, with no special attempt to
+compress consecutive spaces. Each quote character: @kbd{"} is doubled
+so it will be correctly processed by @code{nroff} or @code{troff}.
+
+@item -T
+@itemx --format=tex
+
+Choose an output format suitable for @TeX{} processing. Each output
+line will look like:
+
+@smallexample
+\xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
+@end smallexample
+
+@noindent
+so it will be possible to write a @code{\xx} definition to take care of
+the output typesetting. Note that when references are not being
+produced, that is, neither option @samp{-A} nor option @samp{-r} is
+selected, the last parameter of each @code{\xx} call is inhibited.
+Option @samp{-M} can be used to change @samp{xx} to another macro
+name.
+
+In this output format, some special characters, like @kbd{$}, @kbd{%},
+@kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
+backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
+backslash and a pair of dollar signs (to force mathematical mode). The
+backslash itself produces the sequence @code{\backslash@{@}}.
+Circumflex and tilde diacritics produce the sequence @code{^\@{ @}} and
+@code{~\@{ @}} respectively. Other diacriticized characters of the
+underlying character set produce an appropriate @TeX{} sequence as far
+as possible. The other non-graphical characters, like newline and tab,
+and all other characters which are not part of @sc{ascii}, are merely
+changed to exactly one space, with no special attempt to compress
+consecutive spaces. Let me know how to improve this special character
+processing for @TeX{}.
+
+@end table
+
+
+@node Compatibility in ptx
+@subsection The @sc{gnu} extensions to @code{ptx}
+
+This version of @code{ptx} contains a few features which do not exist in
+System V @code{ptx}. These extra features are suppressed by using the
+@samp{-G} command line option, unless overridden by other command line
+options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
+simple rule is to avoid @samp{-G} if you care about @sc{gnu} extensions.
+Here are the differences between this program and System V @code{ptx}.
+
+@itemize @bullet
+
+@item
+This program can read many input files at once, it always writes the
+resulting concordance on standard output. On the other hand, System V
+@code{ptx} reads only one file and sends the result to standard output
+or, if a second @var{file} parameter is given on the command, to that
+@var{file}.
+
+Having output parameters not introduced by options is a dangerous
+practice which @sc{gnu} avoids as far as possible. So, for using @code{ptx}
+portably between @sc{gnu} and System V, you should always use it with a
+single input file, and always expect the result on standard output. You
+might also want to automatically configure in a @samp{-G} option to
+@code{ptx} calls in products using @code{ptx}, if the configurator finds
+that the installed @code{ptx} accepts @samp{-G}.
+
+@item
+The only options available in System V @code{ptx} are options @samp{-b},
+@samp{-f}, @samp{-g}, @samp{-i}, @samp{-o}, @samp{-r}, @samp{-t} and
+@samp{-w}. All other options are @sc{gnu} extensions and are not repeated in
+this enumeration. Moreover, some options have a slightly different
+meaning when @sc{gnu} extensions are enabled, as explained below.
+
+@item
+By default, concordance output is not formatted for @code{troff} or
+@code{nroff}. It is rather formatted for a dumb terminal. @code{troff}
+or @code{nroff} output may still be selected through option @samp{-O}.
+
+@item
+Unless @samp{-R} option is used, the maximum reference width is
+subtracted from the total output line width. With @sc{gnu} extensions
+disabled, width of references is not taken into account in the output
+line width computations.
+
+@item
+All 256 characters, even @kbd{NUL}s, are always read and processed from
+input file with no adverse effect, even if @sc{gnu} extensions are disabled.
+However, System V @code{ptx} does not accept 8-bit characters, a few
+control characters are rejected, and the tilde @kbd{~} is also rejected.
+
+@item
+Input line length is only limited by available memory, even if @sc{gnu}
+extensions are disabled. However, System V @code{ptx} processes only
+the first 200 characters in each line.
+
+@item
+The break (non-word) characters default to be every character except all
+letters of the underlying character set, diacriticized or not. When @sc{gnu}
+extensions are disabled, the break characters default to space, tab and
+newline only.
+
+@item
+The program makes better use of output line width. If @sc{gnu} extensions
+are disabled, the program rather tries to imitate System V @code{ptx},
+but still, there are some slight disposition glitches this program does
+not completely reproduce.
+
+@item
+The user can specify both an Ignore file and an Only file. This is not
+allowed with System V @code{ptx}.
+
+@end itemize
+
+
+@node Operating on fields within a line
+@chapter Operating on fields within a line
+
+@menu
+* cut invocation:: Print selected parts of lines.
+* paste invocation:: Merge lines of files.
+* join invocation:: Join lines on a common field.
+@end menu
+
+
+@node cut invocation
+@section @code{cut}: Print selected parts of lines
+
+@pindex cut
+@code{cut} writes to standard output selected parts of each line of each
+input file, or standard input if no files are given or for a file name of
+@samp{-}. Synopsis:
+
+@example
+cut [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+In the table which follows, the @var{byte-list}, @var{character-list},
+and @var{field-list} are one or more numbers or ranges (two numbers
+separated by a dash) separated by commas. Bytes, characters, and
+fields are numbered starting at 1. Incomplete ranges may be
+given: @samp{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
+@samp{@var{n}} through end of line or last field.
+
+The program accepts the following options. Also see @ref{Common
+options}.
+
+@table @samp
+
+@item -b @var{byte-list}
+@itemx --bytes=@var{byte-list}
+@opindex -b
+@opindex --bytes
+Print only the bytes in positions listed in @var{byte-list}. Tabs and
+backspaces are treated like any other character; they take up 1 byte.
+
+@item -c @var{character-list}
+@itemx --characters=@var{character-list}
+@opindex -c
+@opindex --characters
+Print only characters in positions listed in @var{character-list}.
+The same as @samp{-b} for now, but internationalization will change
+that. Tabs and backspaces are treated like any other character; they
+take up 1 character.
+
+@item -f @var{field-list}
+@itemx --fields=@var{field-list}
+@opindex -f
+@opindex --fields
+Print only the fields listed in @var{field-list}. Fields are
+separated by a TAB character by default.
+Also print any line that contains no delimiter character, unless
+the @samp{--only-delimited} (@samp{-s}) option is specified
+
+@item -d @var{input_delim_byte}
+@itemx --delimiter=@var{input_delim_byte}
+@opindex -d
+@opindex --delimiter
+For @samp{-f}, fields are separated in the input by the first character
+in @var{input_delim_byte} (default is TAB).
+
+@item -n
+@opindex -n
+Do not split multi-byte characters (no-op for now).
+
+@item -s
+@itemx --only-delimited
+@opindex -s
+@opindex --only-delimited
+For @samp{-f}, do not print lines that do not contain the field separator
+character.
+
+@itemx --output-delimiter=@var{output_delim_string}
+@opindex --output-delimiter
+For @samp{-f}, output fields are separated by @var{output_delim_string}.
+The default is to use the input delimiter.
+
+
+@end table
+
+
+@node paste invocation
+@section @code{paste}: Merge lines of files
+
+@pindex paste
+@cindex merging files
+
+@code{paste} writes to standard output lines consisting of sequentially
+corresponding lines of each given file, separated by a TAB character.
+Standard input is used for a file name of @samp{-} or if no input files
+are given.
+
+Synopsis:
+
+@example
+paste [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -s
+@itemx --serial
+@opindex -s
+@opindex --serial
+Paste the lines of one file at a time rather than one line from each
+file.
+
+@item -d @var{delim-list}
+@itemx --delimiters=@var{delim-list}
+@opindex -d
+@opindex --delimiters
+Consecutively use the characters in @var{delim-list} instead of
+TAB to separate merged lines. When @var{delim-list} is
+exhausted, start again at its beginning.
+
+@end table
+
+
+@node join invocation
+@section @code{join}: Join lines on a common field
+
+@pindex join
+@cindex common field, joining on
+
+@code{join} writes to standard output a line for each pair of input
+lines that have identical join fields. Synopsis:
+
+@example
+join [@var{option}]@dots{} @var{file1} @var{file2}
+@end example
+
+@vindex LC_COLLATE
+Either @var{file1} or @var{file2} (but not both) can be @samp{-},
+meaning standard input. @var{file1} and @var{file2} should be already
+sorted in increasing textual order on the join fields, using the
+collating sequence specified by the @env{LC_COLLATE} locale. Unless
+the @samp{-t} option is given, the input should be sorted ignoring blanks at
+the start of the join field, as in @code{sort -b}. If the
+@samp{--ignore-case} option is given, lines should be sorted without
+regard to the case of characters in the join field, as in @code{sort -f}.
+
+The defaults are: the join field is the first field in each line;
+fields in the input are separated by one or more blanks, with leading
+blanks on the line ignored; fields in the output are separated by a
+space; each output line consists of the join field, the remaining
+fields from @var{file1}, then the remaining fields from @var{file2}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a @var{file-number}
+@opindex -a
+Print a line for each unpairable line in file @var{file-number} (either
+@samp{1} or @samp{2}), in addition to the normal output.
+
+@item -e @var{string}
+@opindex -e
+Replace those output fields that are missing in the input with
+@var{string}.
+
+@item -i
+@itemx --ignore-case
+@opindex -i
+@opindex --ignore-case
+Ignore differences in case when comparing keys.
+With this option, the lines of the input files must be ordered in the same way.
+Use @samp{sort -f} to produce this ordering.
+
+@item -1 @var{field}
+@itemx -j1 @var{field}
+@opindex -1
+@opindex -j1
+Join on field @var{field} (a positive integer) of file 1.
+
+@item -2 @var{field}
+@itemx -j2 @var{field}
+@opindex -2
+@opindex -j2
+Join on field @var{field} (a positive integer) of file 2.
+
+@item -j @var{field}
+Equivalent to @samp{-1 @var{field} -2 @var{field}}.
+
+@item -o @var{field-list}@dots{}
+Construct each output line according to the format in @var{field-list}.
+Each element in @var{field-list} is either the single character @samp{0} or
+has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
+@samp{2} and @var{n} is a positive field number.
+
+A field specification of @samp{0} denotes the join field.
+In most cases, the functionality of the @samp{0} field spec
+may be reproduced using the explicit @var{m.n} that corresponds
+to the join field. However, when printing unpairable lines
+(using either of the @samp{-a} or @samp{-v} options), there is no way
+to specify the join field using @var{m.n} in @var{field-list}
+if there are unpairable lines in both files.
+To give @code{join} that functionality, @sc{posix} invented the @samp{0}
+field specification notation.
+
+The elements in @var{field-list}
+are separated by commas or blanks. Multiple @var{field-list}
+arguments can be given after a single @samp{-o} option; the values
+of all lists given with @samp{-o} are concatenated together.
+All output lines -- including those printed because of any -a or -v
+option -- are subject to the specified @var{field-list}.
+
+@item -t @var{char}
+Use character @var{char} as the input and output field separator.
+
+@item -v @var{file-number}
+Print a line for each unpairable line in file @var{file-number}
+(either @samp{1} or @samp{2}), instead of the normal output.
+
+@end table
+
+In addition, when @sc{gnu} @code{join} is invoked with exactly one argument,
+options @samp{--help} and @samp{--version} are recognized. @xref{Common
+options}.
+
+
+@node Operating on characters
+@chapter Operating on characters
+
+@cindex operating on characters
+
+This commands operate on individual characters.
+
+@menu
+* tr invocation:: Translate, squeeze, and/or delete characters.
+* expand invocation:: Convert tabs to spaces.
+* unexpand invocation:: Convert spaces to tabs.
+@end menu
+
+
+@node tr invocation
+@section @code{tr}: Translate, squeeze, and/or delete characters
+
+@pindex tr
+
+Synopsis:
+
+@example
+tr [@var{option}]@dots{} @var{set1} [@var{set2}]
+@end example
+
+@code{tr} copies standard input to standard output, performing
+one of the following operations:
+
+@itemize @bullet
+@item
+translate, and optionally squeeze repeated characters in the result,
+@item
+squeeze repeated characters,
+@item
+delete characters,
+@item
+delete characters, then squeeze repeated characters from the result.
+@end itemize
+
+The @var{set1} and (if given) @var{set2} arguments define ordered
+sets of characters, referred to below as @var{set1} and @var{set2}. These
+sets are the characters of the input that @code{tr} operates on.
+The @samp{--complement} (@samp{-c}) option replaces @var{set1} with its
+complement (all of the characters that are not in @var{set1}).
+
+@menu
+* Character sets:: Specifying sets of characters.
+* Translating:: Changing one characters to another.
+* Squeezing:: Squeezing repeats and deleting.
+* Warnings in tr:: Warning messages.
+@end menu
+
+
+@node Character sets
+@subsection Specifying sets of characters
+
+@cindex specifying sets of characters
+
+The format of the @var{set1} and @var{set2} arguments resembles
+the format of regular expressions; however, they are not regular
+expressions, only lists of characters. Most characters simply
+represent themselves in these strings, but the strings can contain
+the shorthands listed below, for convenience. Some of them can be
+used only in @var{set1} or @var{set2}, as noted below.
+
+@table @asis
+
+@item Backslash escapes
+@cindex backslash escapes
+
+A backslash followed by a character not listed below causes an error
+message.
+
+@table @samp
+@item \a
+Control-G.
+@item \b
+Control-H.
+@item \f
+Control-L.
+@item \n
+Control-J.
+@item \r
+Control-M.
+@item \t
+Control-I.
+@item \v
+Control-K.
+@item \@var{ooo}
+The character with the value given by @var{ooo}, which is 1 to 3
+octal digits,
+@item \\
+A backslash.
+@end table
+
+@item Ranges
+@cindex ranges
+
+The notation @samp{@var{m}-@var{n}} expands to all of the characters
+from @var{m} through @var{n}, in ascending order. @var{m} should
+collate before @var{n}; if it doesn't, an error results. As an example,
+@samp{0-9} is the same as @samp{0123456789}.
+
+@sc{gnu} @code{tr} does not support the System V syntax that uses square
+brackets to enclose ranges. Translations specified in that format
+sometimes work as expected, since the brackets are often transliterated
+to themselves. However, they should be avoided because they sometimes
+behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
+as well as digits.
+
+Many historically common and even accepted uses of ranges are not
+portable. For example, on @sc{ebcdic} hosts using the @samp{A-Z}
+range will not do what most would expect because @samp{A} through @samp{Z}
+are not contiguous as they are in @sc{ascii}.
+If you can rely on a @sc{posix} compliant version of @code{tr}, then
+the best way to work around this is to use character classes (see below).
+Otherwise, it is most portable (and most ugly) to enumerate the members
+of the ranges.
+
+@item Repeated characters
+@cindex repeated characters
+
+The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
+copies of character @var{c}. Thus, @samp{[y*6]} is the same as
+@samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
+to as many copies of @var{c} as are needed to make @var{set2} as long as
+@var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
+octal, otherwise in decimal.
+
+@item Character classes
+@cindex character classes
+
+The notation @samp{[:@var{class}:]} expands to all of the characters in
+the (predefined) class @var{class}. The characters expand in no
+particular order, except for the @code{upper} and @code{lower} classes,
+which expand in ascending order. When the @samp{--delete} (@samp{-d})
+and @samp{--squeeze-repeats} (@samp{-s}) options are both given, any
+character class can be used in @var{set2}. Otherwise, only the
+character classes @code{lower} and @code{upper} are accepted in
+@var{set2}, and then only if the corresponding character class
+(@code{upper} and @code{lower}, respectively) is specified in the same
+relative position in @var{set1}. Doing this specifies case conversion.
+The class names are given below; an error results when an invalid class
+name is given.
+
+@table @code
+@item alnum
+@opindex alnum
+Letters and digits.
+@item alpha
+@opindex alpha
+Letters.
+@item blank
+@opindex blank
+Horizontal whitespace.
+@item cntrl
+@opindex cntrl
+Control characters.
+@item digit
+@opindex digit
+Digits.
+@item graph
+@opindex graph
+Printable characters, not including space.
+@item lower
+@opindex lower
+Lowercase letters.
+@item print
+@opindex print
+Printable characters, including space.
+@item punct
+@opindex punct
+Punctuation characters.
+@item space
+@opindex space
+Horizontal or vertical whitespace.
+@item upper
+@opindex upper
+Uppercase letters.
+@item xdigit
+@opindex xdigit
+Hexadecimal digits.
+@end table
+
+@item Equivalence classes
+@cindex equivalence classes
+
+The syntax @samp{[=@var{c}=]} expands to all of the characters that are
+equivalent to @var{c}, in no particular order. Equivalence classes are
+a relatively recent invention intended to support non-English alphabets.
+But there seems to be no standard way to define them or determine their
+contents. Therefore, they are not fully implemented in @sc{gnu} @code{tr};
+each character's equivalence class consists only of that character,
+which is of no particular use.
+
+@end table
+
+
+@node Translating
+@subsection Translating
+
+@cindex translating characters
+
+@code{tr} performs translation when @var{set1} and @var{set2} are
+both given and the @samp{--delete} (@samp{-d}) option is not given.
+@code{tr} translates each character of its input that is in @var{set1}
+to the corresponding character in @var{set2}. Characters not in
+@var{set1} are passed through unchanged. When a character appears more
+than once in @var{set1} and the corresponding characters in @var{set2}
+are not all the same, only the final one is used. For example, these
+two commands are equivalent:
+
+@example
+tr aaa xyz
+tr a z
+@end example
+
+A common use of @code{tr} is to convert lowercase characters to
+uppercase. This can be done in many ways. Here are three of them:
+
+@example
+tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
+tr a-z A-Z
+tr '[:lower:]' '[:upper:]'
+@end example
+
+@noindent
+But note that using ranges like @code{a-z} above is not portable.
+
+When @code{tr} is performing translation, @var{set1} and @var{set2}
+typically have the same length. If @var{set1} is shorter than
+@var{set2}, the extra characters at the end of @var{set2} are ignored.
+
+On the other hand, making @var{set1} longer than @var{set2} is not
+portable; @sc{posix.2} says that the result is undefined. In this situation,
+BSD @code{tr} pads @var{set2} to the length of @var{set1} by repeating
+the last character of @var{set2} as many times as necessary. System V
+@code{tr} truncates @var{set1} to the length of @var{set2}.
+
+By default, @sc{gnu} @code{tr} handles this case like BSD @code{tr}. When
+the @samp{--truncate-set1} (@samp{-t}) option is given, @sc{gnu} @code{tr}
+handles this case like the System V @code{tr} instead. This option is
+ignored for operations other than translation.
+
+Acting like System V @code{tr} in this case breaks the relatively common
+BSD idiom:
+
+@example
+tr -cs A-Za-z0-9 '\012'
+@end example
+
+@noindent
+because it converts only zero bytes (the first element in the
+complement of @var{set1}), rather than all non-alphanumerics, to
+newlines.
+
+@noindent
+By the way, the above idiom is not portable because it uses ranges.
+Assuming a @sc{posix} compliant @code{tr}, here is a better way to write it:
+
+@example
+tr -cs '[:alnum:]' '[\n*]'
+@end example
+
+
+@node Squeezing
+@subsection Squeezing repeats and deleting
+
+@cindex squeezing repeat characters
+@cindex deleting characters
+
+When given just the @samp{--delete} (@samp{-d}) option, @code{tr}
+removes any input characters that are in @var{set1}.
+
+When given just the @samp{--squeeze-repeats} (@samp{-s}) option,
+@code{tr} replaces each input sequence of a repeated character that
+is in @var{set1} with a single occurrence of that character.
+
+When given both @samp{--delete} and @samp{--squeeze-repeats}, @code{tr}
+first performs any deletions using @var{set1}, then squeezes repeats
+from any remaining characters using @var{set2}.
+
+The @samp{--squeeze-repeats} option may also be used when translating,
+in which case @code{tr} first performs translation, then squeezes
+repeats from any remaining characters using @var{set2}.
+
+Here are some examples to illustrate various combinations of options:
+
+@itemize @bullet
+
+@item
+Remove all zero bytes:
+
+@example
+tr -d '\000'
+@end example
+
+@item
+Put all words on lines by themselves. This converts all
+non-alphanumeric characters to newlines, then squeezes each string
+of repeated newlines into a single newline:
+
+@example
+tr -cs '[:alnum:]' '[\n*]'
+@end example
+
+@item
+Convert each sequence of repeated newlines to a single newline:
+
+@example
+tr -s '\n'
+@end example
+
+@item
+Find doubled occurrences of words in a document.
+For example, people often write ``the the'' with the duplicated words
+separated by a newline. The bourne shell script below works first
+by converting each sequence of punctuation and blank characters to a
+single newline. That puts each ``word'' on a line by itself.
+Next it maps all uppercase characters to lower case, and finally it
+runs @code{uniq} with the @samp{-d} option to print out only the words
+that were adjacent duplicates.
+
+@example
+#!/bin/sh
+cat "$@@" \
+ | tr -s '[:punct:][:blank:]' '\n' \
+ | tr '[:upper:]' '[:lower:]' \
+ | uniq -d
+@end example
+
+@item
+Deleting a small set of characters is usually straightforward. For example,
+to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
+
+@example
+tr -d axM
+@end example
+
+However, when @samp{-} is one of those characters, it can be tricky because
+@samp{-} has special meanings. Performing the same task as above but also
+removing all @samp{-} characters, we might try @code{tr -d -axM}, but
+that would fail because @code{tr} would try to interpret @samp{-a} as
+a command-line option. Alternatively, we could try putting the hyphen
+inside the string, @code{tr -d a-xM}, but that wouldn't work either because
+it would make @code{tr} interpret @code{a-x} as the range of characters
+@samp{a}@dots{}@samp{x} rather than the three.
+One way to solve the problem is to put the hyphen at the end of the list
+of characters:
+
+@example
+tr -d axM-
+@end example
+
+More generally, use the character class notation @code{[=c=]}
+with @samp{-} (or any other character) in place of the @samp{c}:
+
+@example
+tr -d '[=-=]axM'
+@end example
+
+Note how single quotes are used in the above example to protect the
+square brackets from interpretation by a shell.
+
+@end itemize
+
+
+@node Warnings in tr
+@subsection Warning messages
+
+@vindex POSIXLY_CORRECT
+Setting the environment variable @env{POSIXLY_CORRECT} turns off the
+following warning and error messages, for strict compliance with
+@sc{posix.2}. Otherwise, the following diagnostics are issued:
+
+@enumerate
+
+@item
+When the @samp{--delete} option is given but @samp{--squeeze-repeats}
+is not, and @var{set2} is given, @sc{gnu} @code{tr} by default prints
+a usage message and exits, because @var{set2} would not be used.
+The @sc{posix} specification says that @var{set2} must be ignored in
+this case. Silently ignoring arguments is a bad idea.
+
+@item
+When an ambiguous octal escape is given. For example, @samp{\400}
+is actually @samp{\40} followed by the digit @samp{0}, because the
+value 400 octal does not fit into a single byte.
+
+@end enumerate
+
+@sc{gnu} @code{tr} does not provide complete BSD or System V compatibility.
+For example, it is impossible to disable interpretation of the @sc{posix}
+constructs @samp{[:alpha:]}, @samp{[=c=]}, and @samp{[c*10]}. Also, @sc{gnu}
+@code{tr} does not delete zero bytes automatically, unlike traditional
+Unix versions, which provide no way to preserve zero bytes.
+
+
+@node expand invocation
+@section @code{expand}: Convert tabs to spaces
+
+@pindex expand
+@cindex tabs to spaces, converting
+@cindex converting tabs to spaces
+
+@code{expand} writes the contents of each given @var{file}, or standard
+input if none are given or for a @var{file} of @samp{-}, to standard
+output, with tab characters converted to the appropriate number of
+spaces. Synopsis:
+
+@example
+expand [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+By default, @code{expand} converts all tabs to spaces. It preserves
+backspace characters in the output; they decrement the column count for
+tab calculations. The default action is equivalent to @samp{-8} (set
+tabs every 8 columns).
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -@var{tab1}[,@var{tab2}]@dots{}
+@itemx -t @var{tab1}[,@var{tab2}]@dots{}
+@itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
+@opindex -@var{tab}
+@opindex -t
+@opindex --tabs
+@cindex tabstops, setting
+If only one tab stop is given, set the tabs @var{tab1} spaces apart
+(default is 8). Otherwise, set the tabs at columns @var{tab1},
+@var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
+last tabstop given with single spaces. If the tabstops are specified
+with the @samp{-t} or @samp{--tabs} option, they can be separated by
+blanks as well as by commas.
+
+@item -i
+@itemx --initial
+@opindex -i
+@opindex --initial
+@cindex initial tabs, converting
+Only convert initial tabs (those that precede all non-space or non-tab
+characters) on each line to spaces.
+
+@end table
+
+
+@node unexpand invocation
+@section @code{unexpand}: Convert spaces to tabs
+
+@pindex unexpand
+
+@code{unexpand} writes the contents of each given @var{file}, or
+standard input if none are given or for a @var{file} of @samp{-}, to
+standard output, with strings of two or more space or tab characters
+converted to as many tabs as possible followed by as many spaces as are
+needed. Synopsis:
+
+@example
+unexpand [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+By default, @code{unexpand} converts only initial spaces and tabs (those
+that precede all non space or tab characters) on each line. It
+preserves backspace characters in the output; they decrement the column
+count for tab calculations. By default, tabs are set at every 8th
+column.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -@var{tab1}[,@var{tab2}]@dots{}
+@itemx -t @var{tab1}[,@var{tab2}]@dots{}
+@itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
+@opindex -@var{tab}
+@opindex -t
+@opindex --tabs
+If only one tab stop is given, set the tabs @var{tab1} spaces apart
+instead of the default 8. Otherwise, set the tabs at columns
+@var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave spaces and
+tabs beyond the tabstops given unchanged. If the tabstops are specified
+with the @samp{-t} or @samp{--tabs} option, they can be separated by
+blanks as well as by commas. This option implies the @samp{-a} option.
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Convert all strings of two or more spaces or tabs, not just initial
+ones, to tabs.
+
+@end table
+
+
+@node Directory listing
+@chapter Directory listing
+
+This chapter describes the @code{ls} command and its variants @code{dir}
+and @code{vdir}, which list information about files.
+
+@menu
+* ls invocation:: List directory contents.
+* dir invocation:: Briefly ls.
+* vdir invocation:: Verbosely ls.
+* dircolors invocation:: Color setup for ls, etc.
+@end menu
+
+
+@node ls invocation
+@section @code{ls}: List directory contents
+
+@pindex ls
+@cindex directory listing
+
+The @code{ls} program lists information about files (of any type,
+including directories). Options and file arguments can be intermixed
+arbitrarily, as usual.
+
+For non-option command-line arguments that are directories, by default
+@code{ls} lists the contents of directories, not recursively, and
+omitting files with names beginning with @samp{.}. For other non-option
+arguments, by default @code{ls} lists just the file name. If no
+non-option argument is specified, @code{ls} operates on the current
+directory, acting as if it had been invoked with a single argument of @samp{.}.
+
+@vindex LC_COLLATE
+By default, the output is sorted alphabetically, according to the locale
+settings in effect. @footnote{If you have arranged to use a non-@sc{posix}
+locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @code{ls} may
+produce output that is sorted differently than you're accustomed to.
+In that case, set the @env{LC_COLLATE} environment variable to @samp{C}.}
+If standard output is
+a terminal, the output is in columns (sorted vertically) and control
+characters are output as question marks; otherwise, the output is listed
+one per line and control characters are output as-is.
+
+Because @code{ls} is such a fundamental program, it has accumulated many
+options over the years. They are described in the subsections below;
+within each section, options are listed alphabetically (ignoring case).
+The division of options into the subsections is not absolute, since some
+options affect more than one aspect of @code{ls}'s operation.
+
+Also see @ref{Common options}.
+
+@menu
+* Which files are listed::
+* What information is listed::
+* Sorting the output::
+* More details about version sort::
+* General output formatting::
+* Formatting file timestamps::
+* Formatting the file names::
+@end menu
+
+
+@node Which files are listed
+@subsection Which files are listed
+
+These options determine which files @code{ls} lists information for.
+By default, any files and the contents of any directories on the command
+line are shown.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+List all files in directories, including files that start with @samp{.}.
+
+@item -A
+@itemx --almost-all
+@opindex -A
+@opindex --almost-all
+List all files in directories except for @file{.} and @file{..}.
+
+@item -B
+@itemx --ignore-backups
+@opindex -B
+@opindex --ignore-backups
+@cindex backup files, ignoring
+Do not list files that end with @samp{~}, unless they are given on the
+command line.
+
+@item -d
+@itemx --directory
+@opindex -d
+@opindex --directory
+List just the names of directories, as with other types of files, rather
+than listing their contents.
+
+@item -H
+@itemx --dereference-command-line
+@opindex -H
+@opindex --dereference-command-line
+@cindex symbolic links, dereferencing
+If a command line argument specifies a symbolic link, show information
+for the file the link references rather than for the link itself.
+
+@item -I PATTERN
+@itemx --ignore=PATTERN
+@opindex -I
+@opindex --ignore=@var{pattern}
+Do not list files whose names match the shell pattern (not regular
+expression) @var{pattern} unless they are given on the command line. As
+in the shell, an initial @samp{.} in a file name does not match a
+wildcard at the start of @var{pattern}. Sometimes it is useful
+to give this option several times. For example,
+
+@smallexample
+$ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
+@end smallexample
+
+The first option ignores names of length 3 or more that start with @samp{.},
+the second ignores all two-character names that start with @samp{.}
+except @samp{..}, and the third ignores names that start with @samp{#}.
+
+@item -L
+@itemx --dereference
+@opindex -L
+@opindex --dereference
+@cindex symbolic links, dereferencing
+When showing file information for a symbolic link, show information
+for the file the link references rather than the link itself.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+@cindex recursive directory listing
+@cindex directory listing, recursive
+List the contents of all directories recursively.
+
+@end table
+
+
+@node What information is listed
+@subsection What information is listed
+
+These options affect the information that @code{ls} displays. By
+default, only file names are shown.
+
+@table @samp
+
+@item -D
+@itemx --dired
+@opindex -D
+@opindex --dired
+@cindex dired Emacs mode support
+With the long listing (@samp{-l}) format, print an additional line after
+the main output:
+
+@example
+//DIRED// @var{beg1 end1 beg2 end2 @dots{}}
+@end example
+
+@noindent
+The @var{begN} and @var{endN} are unsigned integers that record the
+byte position of the beginning and end of each file name in the output.
+This makes it easy for Emacs to find the names, even when they contain
+unusual characters such as space or newline, without fancy searching.
+
+If directories are being listed recursively (@code{-R}), output a similar
+line after each subdirectory:
+@example
+//SUBDIRED// @var{format} @var{beg1 end1 @dots{}}
+@end example
+
+Finally, output a line of the form:
+@example
+//DIRED-OPTIONS// --quoting-style=@var{word}
+@end example
+where @var{word} is the quoting style (@pxref{Formatting the file names}).
+
+@item --full-time
+@opindex --full-time
+Produce long format directory listings, and list times in full. It is
+equivalent to using @option{--format=long} with
+@option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
+
+@item -g
+@opindex -g
+Produce long format directory listings, but don't display owner information.
+
+@item -G
+@itemx --no-group
+@opindex -G
+@opindex --no-group
+Inhibit display of group information in a long format directory listing.
+(This is the default in some non-@sc{gnu} versions of @code{ls}, so we
+provide this option for compatibility.)
+
+@item -h
+@itemx --human-readable
+@opindex -h
+@opindex --human-readable
+@cindex human-readable output
+Append a size letter such as @samp{M} for megabytes to each size.
+Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
+Use the @samp{--si} option if you prefer powers of 1000.
+
+@item -i
+@itemx --inode
+@opindex -i
+@opindex --inode
+@cindex inode number, printing
+Print the inode number (also called the file serial number and index
+number) of each file to the left of the file name. (This number
+uniquely identifies each file within a particular filesystem.)
+
+@item -l
+@itemx --format=long
+@itemx --format=verbose
+@opindex -l
+@opindex --format
+@opindex long ls @r{format}
+@opindex verbose ls @r{format}
+In addition to the name of each file, print the file type, permissions,
+number of hard links, owner name, group name, size in bytes, and
+timestamp (@pxref{Formatting file timestamps}), normally
+the modification time.
+
+For each directory that is listed, preface the files with a line
+@samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
+for all files in that directory. The block size currently defaults to 1024
+bytes, but this can be overridden (@pxref{Block size}).
+The @var{blocks} computed counts each hard link separately;
+this is arguably a deficiency.
+
+@cindex permissions, output by @code{ls}
+The permissions listed are similar to symbolic mode specifications
+(@pxref{Symbolic Modes}). But @code{ls} combines multiple bits into the
+third character of each set of permissions as follows:
+@table @samp
+@item s
+If the setuid or setgid bit and the corresponding executable bit
+are both set.
+
+@item S
+If the setuid or setgid bit is set but the corresponding executable bit
+is not set.
+
+@item t
+If the sticky bit and the other-executable bit are both set.
+
+@item T
+If the sticky bit is set but the other-executable bit is not set.
+
+@item x
+If the executable bit is set and none of the above apply.
+
+@item -
+Otherwise.
+@end table
+
+Following the permission bits is a single character that specifies
+whether an alternate access method applies to the file. When that
+character is a space, there is no alternate access method. When it
+is a printing character (e.g., @samp{+}), then there is such a method.
+
+@item -n
+@itemx --numeric-uid-gid
+@opindex -n
+@opindex --numeric-uid-gid
+@cindex numeric uid and gid
+Produce long format directory listings, but
+display numeric UIDs and GIDs instead of the owner and group names.
+
+@item -o
+@opindex -o
+Produce long format directory listings, but don't display group information.
+It is equivalent to using @samp{--format=long} with @samp{--no-group} .
+
+@item -s
+@itemx --size
+@opindex -s
+@opindex --size
+@cindex disk allocation
+@cindex size of files, reporting
+Print the disk allocation of each file to the left of the file name.
+This is the amount of disk space used by the file, which is usually a
+bit more than the file's size, but it can be less if the file has holes.
+
+Normally the disk allocation is printed in units of
+1024 bytes, but this can be overridden (@pxref{Block size}).
+
+@cindex NFS mounts from BSD to HP-UX
+For files that are NFS-mounted from an HP-UX system to a BSD system,
+this option reports sizes that are half the correct values. On HP-UX
+systems, it reports sizes that are twice the correct values for files
+that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
+it also affects the HP-UX @code{ls} program.
+
+@itemx --si
+@opindex --si
+@cindex SI output
+Append a size letter such as @samp{M} for megabytes to each size. (SI
+is the International System of Units, which defines these letters as
+prefixes.) Powers of 1000 are used, not 1024; @samp{M} stands for
+1,000,000 bytes. Use the @samp{-h} or @samp{--human-readable} option if
+you prefer powers of 1024.
+
+@end table
+
+
+@node Sorting the output
+@subsection Sorting the output
+
+@cindex sorting @code{ls} output
+These options change the order in which @code{ls} sorts the information
+it outputs. By default, sorting is done by character code (e.g., ASCII
+order).
+
+@table @samp
+
+@item -c
+@itemx --time=ctime
+@itemx --time=status
+@itemx --time=use
+@opindex -c
+@opindex --time
+@opindex ctime@r{, printing or sorting by}
+@opindex status time@r{, printing or sorting by}
+@opindex use time@r{, printing or sorting files by}
+If the long listing format (e.g., @samp{-l}, @samp{-o}) is being used,
+print the status change time (the @samp{ctime} in the inode) instead of
+the modification time.
+When explicitly sorting by time (@samp{--sort=time} or @samp{-t})
+or when not using a long listing format,
+sort according to the status change time.
+
+@item -f
+@opindex -f
+@cindex unsorted directory listing
+@cindex directory order, listing by
+Primarily, like @samp{-U}---do not sort; list the files in whatever
+order they are stored in the directory. But also enable @samp{-a} (list
+all files) and disable @samp{-l}, @samp{--color}, and @samp{-s} (if they
+were specified before the @samp{-f}).
+
+@item -r
+@itemx --reverse
+@opindex -r
+@opindex --reverse
+@cindex reverse sorting
+Reverse whatever the sorting method is---e.g., list files in reverse
+alphabetical order, youngest first, smallest first, or whatever.
+
+@item -S
+@itemx --sort=size
+@opindex -S
+@opindex --sort
+@opindex size of files@r{, sorting files by}
+Sort by file size, largest first.
+
+@item -t
+@itemx --sort=time
+@opindex -t
+@opindex --sort
+@opindex modification time@r{, sorting files by}
+Sort by modification time (the @samp{mtime} in the inode), newest first.
+
+@item -u
+@itemx --time=atime
+@itemx --time=access
+@opindex -u
+@opindex --time
+@opindex use time@r{, printing or sorting files by}
+@opindex atime@r{, printing or sorting files by}
+@opindex access time@r{, printing or sorting files by}
+If the long listing format (e.g., @samp{--format=long}) is being used,
+print the last access time (the @samp{atime} in the inode).
+When explicitly sorting by time (@samp{--sort=time} or @samp{-t})
+or when not using a long listing format, sort according to the access time.
+
+@item -U
+@itemx --sort=none
+@opindex -U
+@opindex --sort
+@opindex none@r{, sorting option for @code{ls}}
+Do not sort; list the files in whatever order they are
+stored in the directory. (Do not do any of the other unrelated things
+that @samp{-f} does.) This is especially useful when listing very large
+directories, since not doing any sorting can be noticeably faster.
+
+@item -v
+@itemx --sort=version
+@opindex -v
+@opindex --sort
+@opindex version@r{, sorting option for @code{ls}}
+Sort by version name and number, lowest first. It behaves like a default
+sort, except that each sequence of decimal digits is treated numerically
+as an index/version number. (@xref{More details about version sort}.)
+
+@item -X
+@itemx --sort=extension
+@opindex -X
+@opindex --sort
+@opindex extension@r{, sorting files by}
+Sort directory contents alphabetically by file extension (characters
+after the last @samp{.}); files with no extension are sorted first.
+
+@end table
+
+
+@node More details about version sort
+@subsection More details about version sort
+
+The version sort takes into account the fact that file names frequently include
+indices or version numbers. Standard sorting functions usually do not produce
+the ordering that people expect because comparisons are made on a
+character-by-character basis. The version
+sort addresses this problem, and is especially useful when browsing
+directories that contain many files with indices/version numbers in their
+names:
+
+@example
+ > ls -1 > ls -1v
+ foo.zml-1.gz foo.zml-1.gz
+ foo.zml-100.gz foo.zml-2.gz
+ foo.zml-12.gz foo.zml-6.gz
+ foo.zml-13.gz foo.zml-12.gz
+ foo.zml-2.gz foo.zml-13.gz
+ foo.zml-25.gz foo.zml-25.gz
+ foo.zml-6.gz foo.zml-100.gz
+@end example
+
+Note also that numeric parts with leading zeroes are considered as
+fractional one:
+
+@example
+ > ls -1 > ls -1v
+ abc-1.007.tgz abc-1.007.tgz
+ abc-1.012b.tgz abc-1.01a.tgz
+ abc-1.01a.tgz abc-1.012b.tgz
+@end example
+
+@node General output formatting
+@subsection General output formatting
+
+These options affect the appearance of the overall output.
+
+@table @samp
+
+@item -1
+@itemx --format=single-column
+@opindex -1
+@opindex --format
+@opindex single-column @r{output of files}
+List one file per line. This is the default for @code{ls} when standard
+output is not a terminal.
+
+@item -C
+@itemx --format=vertical
+@opindex -C
+@opindex --format
+@opindex vertical @r{sorted files in columns}
+List files in columns, sorted vertically. This is the default for
+@code{ls} if standard output is a terminal. It is always the default
+for the @code{dir} and @code{d} programs.
+@sc{gnu} @code{ls} uses variable width columns to display as many files as
+possible in the fewest lines.
+
+@item --color [=@var{when}]
+@opindex --color
+@cindex color, distinguishing file types with
+Specify whether to use color for distinguishing file types. @var{when}
+may be omitted, or one of:
+@itemize @bullet
+@item none
+@vindex none @r{color option}
+- Do not use color at all. This is the default.
+@item auto
+@vindex auto @r{color option}
+@cindex terminal, using color iff
+- Only use color if standard output is a terminal.
+@item always
+@vindex always @r{color option}
+- Always use color.
+@end itemize
+Specifying @samp{--color} and no @var{when} is equivalent to
+@samp{--color=always}.
+Piping a colorized listing through a pager like @code{more} or
+@code{less} usually produces unreadable results. However, using
+@code{more -f} does seem to work.
+
+@item -F
+@itemx --classify
+@itemx --indicator-style=classify
+@opindex -F
+@opindex --classify
+@opindex --indicator-style
+@cindex file type and executables, marking
+@cindex executables and file type, marking
+Append a character to each file name indicating the file type. Also,
+for regular files that are executable, append @samp{*}. The file type
+indicators are @samp{/} for directories, @samp{@@} for symbolic links,
+@samp{|} for FIFOs, @samp{=} for sockets, and nothing for regular files.
+
+@item --indicator-style=@var{word}
+@opindex --indicator-style
+Append a character indicator with style @var{word} to entry names,
+as follows:
+@table @samp
+@item none
+Do not append any character indicator; this is the default.
+@item file-type
+Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
+for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
+the same as the @samp{-p} or @samp{--file-type} option.
+@item classify
+Append @samp{*} for executable regular files, otherwise behave as for
+@samp{file-type}. This is the same as the @samp{-F} or
+@samp{--classify} option.
+@end table
+
+@item -k
+@itemx --kilobytes
+@opindex -k
+@opindex --kilobytes
+Print file sizes in 1024-byte blocks, overriding the default block
+size (@pxref{Block size}).
+
+@item -m
+@itemx --format=commas
+@opindex -m
+@opindex --format
+@opindex commas@r{, outputting between files}
+List files horizontally, with as many as will fit on each line,
+separated by @samp{, } (a comma and a space).
+
+@item -p
+@itemx --file-type
+@itemx --indicator-style=file-type
+@opindex --file-type
+@opindex --indicator-style
+@cindex file type, marking
+Append a character to each file name indicating the file type. This is
+like @samp{-F}, except that executables are not marked.
+
+@item -x @var{format}
+@itemx --format=across
+@itemx --format=horizontal
+@opindex -x
+@opindex --format
+@opindex across@r{, listing files}
+@opindex horizontal@r{, listing files}
+List the files in columns, sorted horizontally.
+
+@item -T @var{cols}
+@itemx --tabsize=@var{cols}
+@opindex -T
+@opindex --tabsize
+Assume that each tabstop is @var{cols} columns wide. The default is 8.
+@code{ls} uses tabs where possible in the output, for efficiency. If
+@var{cols} is zero, do not use tabs at all.
+
+@item -w
+@itemx --width=@var{cols}
+@opindex -w
+@opindex --width
+@vindex COLUMNS
+Assume the screen is @var{cols} columns wide. The default is taken
+from the terminal settings if possible; otherwise the environment
+variable @env{COLUMNS} is used if it is set; otherwise the default
+is 80.
+
+@end table
+
+
+@node Formatting file timestamps
+@subsection Formatting file timestamps
+
+By default, file timestamps are output in abbreviated form. For files
+with a time more than six months old or in the future, the timestamp
+contains the year instead of the time of day. If the timestamp contains
+today's date with the year rather than a time of day, the file's time is
+in the future, which means you probably have clock skew problems which
+may break programs like @command{make} that rely on file times.
+
+The following option changes how file timestamps are printed.
+
+@table @samp
+@item --time-style=@var{word}
+@opindex --time-style
+@cindex time style
+Use style @var{word} to output file timestamps. The @var{word} should
+be one of the following:
+
+@table @samp
+@item full-iso
+List timestamps in full, rather than using the standard abbreviation
+heuristics. The format is @sc{iso} 8601 date, time, and time zone
+format with nanosecond precision, e.g., @samp{2001-05-14
+23:45:56.477817180 -0700}. It's not possible to change the format, but
+you can extract out the date string with @code{cut} and then pass the
+result to @code{date -d}. @xref{date invocation, @code{date}
+invocation, , sh-utils, Shell utilities}.
+
+This is useful because the time output includes all the information that
+is available from the operating system. For example, this can help
+when you have a Makefile that is not regenerating files properly.
+
+@item iso
+Use @sc{iso}-style time stamps like @samp{2001-05-14@ } and @samp{05-14
+23:45}.
+
+@item locale
+@vindex LC_ALL
+@vindex LC_TIME
+@vindex LANG
+Use locale-dependent dates like @samp{touko@ @ 14 2001} and @samp{touko@
+@ 14 23:45}, time stamps that might occur in a Finnish locale. The
+locale for formatting timestamps is specified by the first of three
+environment variables @env{LC_ALL}, @env{LC_TIME}, @env{LANG} that is
+set.
+
+@item posix-iso
+Use traditional @sc{posix}-locale dates like @samp{May 14@ @ 2001} and
+@samp{May 14 23:45} unless the user specifies a non-@sc{posix} locale,
+in which case use @sc{iso}-style dates. This is the default.
+@end table
+@end table
+
+@vindex TIME_STYLE
+You can specify the default value of the @option{--time-style} option
+with the environment variable @env{TIME_STYLE}. @sc{gnu} Emacs 21 and
+later can parse @sc{iso} dates, but older Emacs versions do not, so if
+you are using an older version of Emacs and specify a non-@sc{posix}
+locale, you may need to set @samp{TIME_STYLE="locale"}.
+
+
+@node Formatting the file names
+@subsection Formatting the file names
+
+These options change how file names themselves are printed.
+
+@table @samp
+
+@item -b
+@itemx --escape
+@itemx --quoting-style=escape
+@opindex -b
+@opindex --escape
+@opindex --quoting-style
+@cindex backslash sequences for file names
+Quote nongraphic characters in file names using alphabetic and octal
+backslash sequences like those used in C.
+
+@item -N
+@itemx --literal
+@opindex -N
+@opindex --literal
+Do not quote file names.
+
+@item -q
+@itemx --hide-control-chars
+@opindex -q
+@opindex --hide-control-chars
+Print question marks instead of nongraphic characters in file names.
+This is the default if the output is a terminal and the program is
+@code{ls}.
+
+@item -Q
+@itemx --quote-name
+@itemx --quoting-style=c
+@opindex -Q
+@opindex --quote-name
+@opindex --quoting-style
+Enclose file names in double quotes and quote nongraphic characters as
+in C.
+
+@item --quoting-style=@var{word}
+@opindex --quoting-style
+@cindex quoting style
+Use style @var{word} to quote output names. The @var{word} should
+be one of the following:
+@table @samp
+@item literal
+Output names as-is.
+@item shell
+Quote names for the shell if they contain shell metacharacters or would
+cause ambiguous output.
+@item shell-always
+Quote names for the shell, even if they would normally not require quoting.
+@item c
+Quote names as for a C language string; this is the same as the
+@samp{-Q} or @samp{--quote-name} option.
+@item escape
+Quote as with @samp{c} except omit the surrounding double-quote
+characters; this is the same as the @samp{-b} or @samp{--escape} option.
+@item clocale
+Quote as with @samp{c} except use quotation marks appropriate for the
+locale.
+@item locale
+@c Use @t instead of @samp to avoid duplicate quoting in some output styles.
+Like @samp{clocale}, but quote @t{`like this'} instead of @t{"like
+this"} in the default C locale. This looks nicer on many displays.
+@end table
+
+You can specify the default value of the @samp{--quoting-style} option
+with the environment variable @env{QUOTING_STYLE}. If that environment
+variable is not set, the default value is @samp{literal}, but this
+default may change to @samp{shell} in a future version of this package.
+
+@item --show-control-chars
+@opindex --show-control-chars
+Print nongraphic characters as-is in file names.
+This is the default unless the output is a terminal and the program is
+@code{ls}.
+
+@end table
+
+
+@node dir invocation
+@section @code{dir}: Briefly list directory contents
+
+@pindex dir
+@cindex directory listing, brief
+
+@code{dir} (also installed as @code{d}) is equivalent to @code{ls -C
+-b}; that is, by default files are listed in columns, sorted vertically,
+and special characters are represented by backslash escape sequences.
+
+@xref{ls invocation, @code{ls}}.
+
+
+@node vdir invocation
+@section @code{vdir}: Verbosely list directory contents
+
+@pindex vdir
+@cindex directory listing, verbose
+
+@code{vdir} (also installed as @code{v}) is equivalent to @code{ls -l
+-b}; that is, by default files are listed in long format and special
+characters are represented by backslash escape sequences.
+
+@node dircolors invocation
+@section @code{dircolors}: Color setup for @code{ls}
+
+@pindex dircolors
+@cindex color setup
+@cindex setup for color
+
+@code{dircolors} outputs a sequence of shell commands to set up the
+terminal for color output from @code{ls} (and @code{dir}, etc.).
+Typical usage:
+
+@example
+eval `dircolors [@var{option}]@dots{} [@var{file}]`
+@end example
+
+If @var{file} is specified, @code{dircolors} reads it to determine which
+colors to use for which file types and extensions. Otherwise, a
+precompiled database is used. For details on the format of these files,
+run @samp{dircolors --print-database}.
+
+@vindex LS_COLORS
+@vindex SHELL @r{environment variable, and color}
+The output is a shell command to set the @env{LS_COLORS} environment
+variable. You can specify the shell syntax to use on the command line,
+or @code{dircolors} will guess it from the value of the @env{SHELL}
+environment variable.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -b
+@itemx --sh
+@itemx --bourne-shell
+@opindex -b
+@opindex --sh
+@opindex --bourne-shell
+@cindex Bourne shell syntax for color setup
+@cindex @code{sh} syntax for color setup
+Output Bourne shell commands. This is the default if the @env{SHELL}
+environment variable is set and does not end with @samp{csh} or
+@samp{tcsh}.
+
+@item -c
+@itemx --csh
+@itemx --c-shell
+@opindex -c
+@opindex --csh
+@opindex --c-shell
+@cindex C shell syntax for color setup
+@cindex @code{csh} syntax for color setup
+Output C shell commands. This is the default if @code{SHELL} ends with
+@code{csh} or @code{tcsh}.
+
+@item -p
+@itemx --print-database
+@opindex -p
+@opindex --print-database
+@cindex color database, printing
+@cindex database for color setup, printing
+@cindex printing color database
+Print the (compiled-in) default color configuration database. This
+output is itself a valid configuration file, and is fairly descriptive
+of the possibilities.
+
+@end table
+
+
+@node Basic operations
+@chapter Basic operations
+
+@cindex manipulating files
+
+This chapter describes the commands for basic file manipulation:
+copying, moving (renaming), and deleting (removing).
+
+@menu
+* cp invocation:: Copy files.
+* dd invocation:: Convert and copy a file.
+* install invocation:: Copy files and set attributes.
+* mv invocation:: Move (rename) files.
+* rm invocation:: Remove files or directories.
+* shred invocation:: Remove files more securely.
+@end menu
+
+
+@node cp invocation
+@section @code{cp}: Copy files and directories
+
+@pindex cp
+@cindex copying files and directories
+@cindex files, copying
+@cindex directories, copying
+
+@code{cp} copies files (or, optionally, directories). The copy is
+completely independent of the original. You can either copy one file to
+another, or copy arbitrarily many files to a destination directory.
+Synopsis:
+
+@example
+cp [@var{option}]@dots{} @var{source} @var{dest}
+cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
+@end example
+
+If the last argument names an existing directory, @code{cp} copies each
+@var{source} file into that directory (retaining the same name).
+Otherwise, if only two files are given, it copies the first onto the
+second. It is an error if the last argument is not a directory and more
+than two non-option arguments are given.
+
+Generally, files are written just as they are read. For exceptions,
+see the @samp{--sparse} option below.
+
+By default, @command{cp} does not copy directories. However, the
+@option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
+copy recursively by descending into source directories and copying files
+to corresponding destination directories.
+
+By default, @command{cp} follows symbolic links only when not copying
+recursively. This default can be overridden with the
+@option{--no-dereference} (@option{-d}), @option{--dereference}
+(@option{-L}), and @option{-H} options. If more than one of these
+options is specified, the last one silently overrides the others.
+
+@cindex self-backups
+@cindex backups, making only
+@code{cp} generally refuses to copy a file onto itself, with the
+following exception: if @samp{--force --backup} is specified with
+@var{source} and @var{dest} identical, and referring to a regular file,
+@code{cp} will make a backup file, either regular or numbered, as
+specified in the usual ways (@pxref{Backup options}). This is useful when
+you simply want to make a backup of an existing file before changing it.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -a
+@itemx --archive
+@opindex -a
+@opindex --archive
+Preserve as much as possible of the structure and attributes of the
+original files in the copy (but do not attempt to preserve internal
+directory structure; i.e., @samp{ls -U} may list the entries in a copied
+directory in a different order).
+Equivalent to @samp{-dpR}.
+
+@item -b
+@itemx @w{@kbd{--backup}[=@var{method}]}
+@opindex -b
+@opindex --backup
+@vindex VERSION_CONTROL
+@cindex backups, making
+@xref{Backup options}.
+Make a backup of each file that would otherwise be overwritten or removed.
+As a special case, @code{cp} makes a backup of @var{source} when the force
+and backup options are given and @var{source} and @var{dest} are the same
+name for an existing, regular file. One useful application of this
+combination of options is this tiny Bourne shell script:
+
+@example
+#!/bin/sh
+# Usage: backup FILE...
+# Create a @sc{gnu}-style backup of each listed FILE.
+for i in "$@"; do
+ cp --backup --force "$i" "$i"
+done
+@end example
+
+@item -d
+@itemx --no-dereference
+@opindex -d
+@opindex --no-dereference
+@cindex symbolic links, copying
+@cindex hard links, preserving
+Copy symbolic links as symbolic links rather than copying the files that
+they point to, and preserve hard links between source files in the
+copies.
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+When copying without this option and an existing destination file cannot
+be opened for writing, the copy fails. However, with @samp{--force}),
+when a destination file cannot be opened, @code{cp} then unlinks it and
+tries to open it again. Contrast this behavior with that enabled by
+@samp{--link} and @samp{--symbolic-link}, whereby the destination file
+is never opened but rather is unlinked unconditionally. Also see the
+description of @samp{--remove-destination}.
+
+@item -H
+@opindex -H
+If a command line argument specifies a symbolic link, then copy the
+file it points to rather than the symbolic link itself. However,
+copy (preserving its nature) any symbolic link that is encountered
+via recursive traversal.
+
+@item -i
+@itemx --interactive
+@opindex -i
+@opindex --interactive
+Prompt whether to overwrite existing regular destination files.
+
+@item -l
+@itemx --link
+@opindex -l
+@opindex --link
+Make hard links instead of copies of non-directories.
+
+@item -L
+@itemx --dereference
+@opindex -L
+@opindex --dereference
+Always follow symbolic links.
+
+@item -p
+@itemx --preserve
+@opindex -p
+@opindex --preserve
+@cindex file information, preserving
+Preserve the original files' owner, group, permissions, and timestamps.
+In the absence of this option, each destination file is created with the
+permissions of the corresponding source file, minus the bits set in the
+umask. @xref{File permissions}.
+
+@item -P
+@itemx --parents
+@opindex -P
+@opindex --parents
+@cindex parent directories and @code{cp}
+Form the name of each destination file by appending to the target
+directory a slash and the specified name of the source file. The last
+argument given to @code{cp} must be the name of an existing directory.
+For example, the command:
+
+@example
+cp --parents a/b/c existing_dir
+@end example
+
+@noindent
+copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
+any missing intermediate directories.
+
+Warning: the meaning of @option{-P} will change in the future to conform
+to @sc{posix}. Use @option{--parents} for the old meaning, and
+@option{--no-dereference} for the new.
+
+@item -r
+@cindex directories, copying recursively
+@cindex copying directories recursively
+@cindex recursively copying directories
+@cindex non-directories, copying as special files
+Copy directories recursively, copying any non-directories and special
+files (e.g., symbolic links, FIFOs and device files) as if they were
+regular files. This means trying to read the data in each source
+file and writing it to the destination. It is usually a mistake to
+apply @code{cp -r} to special files like FIFOs and the ones typically
+found in the @file{/dev} directory. In most cases, @code{cp -r}
+will hang indefinitely trying to read from FIFOs and special files
+like @file{/dev/console}, and it will fill up your destination disk
+if you use it to copy @file{/dev/zero}.
+Use the @samp{--recursive} (@samp{-R}) option instead if you want
+to copy special files, preserving their special nature
+rather than reading from them to copy their contents.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+Copy directories recursively, preserving non-directories (contrast with
+@samp{-r} just above).
+
+@item --remove-destination
+@opindex --remove-destination
+Remove each existing destination file before attempting to open it
+(contrast with @option{-f} above).
+
+@item --sparse=@var{when}
+@opindex --sparse=@var{when}
+@cindex sparse files, copying
+@cindex holes, copying files with
+@findex read @r{system call, and holes}
+A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
+does not occupy any physical disk blocks; the @samp{read} system call
+reads these as zeroes. This can both save considerable disk space and
+increase speed, since many binary files contain lots of consecutive zero
+bytes. By default, @code{cp} detects holes in input source files via a crude
+heuristic and makes the corresponding output file sparse as well.
+
+The @var{when} value can be one of the following:
+@table @samp
+@item auto
+The default behavior: the output file is sparse if the input file is sparse.
+
+@item always
+Always make the output file sparse. This is useful when the input
+file resides on a filesystem that does not support sparse files (the
+most notable example is @samp{efs} filesystems in SGI IRIX 5.3 and
+earlier), but the output file is on another type of filesystem.
+
+@item never
+Never make the output file sparse.
+This is useful in creating a file for use with the @code{mkswap} command,
+since such a file must not have any holes.
+@end table
+
+@itemx @w{@kbd{--strip-trailing-slashes}}
+@opindex --strip-trailing-slashes
+@cindex stripping trailing slashes
+Remove any trailing slashes from each @var{source} argument.
+@xref{Trailing slashes}.
+
+@item -s
+@itemx --symbolic-link
+@opindex -s
+@opindex --symbolic-link
+@cindex symbolic links, copying with
+Make symbolic links instead of copies of non-directories. All source
+file names must be absolute (starting with @samp{/}) unless the
+destination files are in the current directory. This option merely
+results in an error message on systems that do not support symbolic links.
+
+@item -S @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -S
+@opindex --suffix
+Append @var{suffix} to each backup file made with @samp{-b}.
+@xref{Backup options}.
+
+@itemx @w{@kbd{--target-directory}=@var{directory}}
+@opindex --target-directory
+@cindex target directory
+@cindex destination directory
+Specify the destination @var{directory}.
+@xref{Target directory}.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before copying it.
+
+@item -V @var{method}
+@itemx --version-control=@var{method}
+@opindex -V
+@opindex --version-control
+Change the type of backups made with @samp{-b}. The @var{method}
+argument can be @samp{none} (or @samp{off}), @samp{numbered} (or
+@samp{t}), @samp{existing} (or @samp{nil}), or @samp{never} (or
+@samp{simple}). @xref{Backup options}.
+
+@item -x
+@itemx --one-file-system
+@opindex -x
+@opindex --one-file-system
+@cindex filesystems, omitting copying to different
+Skip subdirectories that are on different filesystems from the one that
+the copy started on.
+However, mount point directories @emph{are} copied.
+
+@end table
+
+
+@node dd invocation
+@section @code{dd}: Convert and copy a file
+
+@pindex dd
+@cindex converting while copying a file
+
+@code{dd} copies a file (from standard input to standard output, by
+default) with a changeable I/O block size, while optionally performing
+conversions on it. Synopsis:
+
+@example
+dd [@var{option}]@dots{}
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@cindex multipliers after numbers
+The numeric-valued options below (@var{bytes} and @var{blocks}) can be
+followed by a multiplier: @samp{b}=512, @samp{c}=1,
+@samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
+standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
+
+Use different @command{dd} invocations to use different block sizes for
+skipping and I/O. For example, the following shell commands copy data
+in 512 kB blocks between a disk and a tape, but do not save or restore a
+4 kB label at the start of the disk:
+
+@example
+disk=/dev/rdsk/c0t1d0s2
+tape=/dev/rmt/0
+
+# Copy all but the label from disk to tape.
+(dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
+
+# Copy from tape back to disk, but leave the disk label alone.
+(dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
+@end example
+
+@table @samp
+
+@item if=@var{file}
+@opindex if
+Read from @var{file} instead of standard input.
+
+@item of=@var{file}
+@opindex of
+Write to @var{file} instead of standard output. Unless
+@samp{conv=notrunc} is given, @code{dd} truncates @var{file} to zero
+bytes (or the size specified with @samp{seek=}).
+
+@item ibs=@var{bytes}
+@opindex ibs
+@cindex block size of input
+@cindex input block size
+Read @var{bytes} bytes at a time.
+
+@item obs=@var{bytes}
+@opindex obs
+@cindex block size of output
+@cindex output block size
+Write @var{bytes} bytes at a time.
+
+@item bs=@var{bytes}
+@opindex bs
+@cindex block size
+Both read and write @var{bytes} bytes at a time. This overrides
+@samp{ibs} and @samp{obs}.
+
+@item cbs=@var{bytes}
+@opindex cbs
+@cindex block size of conversion
+@cindex conversion block size
+Convert @var{bytes} bytes at a time.
+
+@item skip=@var{blocks}
+@opindex skip
+Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
+
+@item seek=@var{blocks}
+@opindex seek
+Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
+
+@item count=@var{blocks}
+@opindex count
+Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
+of everything until the end of the file.
+
+@item conv=@var{conversion}[,@var{conversion}]@dots{}
+@opindex conv
+Convert the file as specified by the @var{conversion} argument(s).
+(No spaces around any comma(s).)
+
+Conversions:
+
+@table @samp
+
+@item ascii
+@opindex ascii@r{, converting to}
+Convert EBCDIC to ASCII.
+
+@item ebcdic
+@opindex ebcdic@r{, converting to}
+Convert ASCII to EBCDIC.
+
+@item ibm
+@opindex alternate ebcdic@r{, converting to}
+Convert ASCII to alternate EBCDIC.
+
+@item block
+@opindex block @r{(space-padding)}
+For each line in the input, output @samp{cbs} bytes, replacing the
+input newline with a space and padding with spaces as necessary.
+
+@item unblock
+@opindex unblock
+Replace trailing spaces in each @samp{cbs}-sized input block with a
+newline.
+
+@item lcase
+@opindex lcase@r{, converting to}
+Change uppercase letters to lowercase.
+
+@item ucase
+@opindex ucase@r{, converting to}
+Change lowercase letters to uppercase.
+
+@item swab
+@opindex swab @r{(byte-swapping)}
+@cindex byte-swapping
+Swap every pair of input bytes. @sc{gnu} @code{dd}, unlike others, works
+when an odd number of bytes are read---the last byte is simply copied
+(since there is nothing to swap it with).
+
+@item noerror
+@opindex noerror
+@cindex read errors, ignoring
+Continue after read errors.
+
+@item notrunc
+@opindex notrunc
+@cindex truncating output file, avoiding
+Do not truncate the output file.
+
+@item sync
+@opindex sync @r{(padding with nulls)}
+Pad every input block to size of @samp{ibs} with trailing zero bytes.
+When used with @samp{block} or @samp{unblock}, pad with spaces instead of
+zero bytes.
+@end table
+
+@end table
+
+
+@node install invocation
+@section @code{install}: Copy files and set attributes
+
+@pindex install
+@cindex copying files and setting attributes
+
+@code{install} copies files while setting their permission modes and, if
+possible, their owner and group. Synopses:
+
+@example
+install [@var{option}]@dots{} @var{source} @var{dest}
+install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
+install -d [@var{option}]@dots{} @var{directory}@dots{}
+@end example
+
+In the first of these, the @var{source} file is copied to the @var{dest}
+target file. In the second, each of the @var{source} files are copied
+to the destination @var{directory}. In the last, each @var{directory}
+(and any missing parent directories) is created.
+
+@cindex Makefiles, installing programs in
+@code{install} is similar to @code{cp}, but allows you to control the
+attributes of destination files. It is typically used in Makefiles to
+copy programs into their destination directories. It refuses to copy
+files onto themselves.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx @w{@kbd{--backup}[=@var{method}]}
+@opindex -b
+@opindex --backup
+@vindex VERSION_CONTROL
+@cindex backups, making
+@xref{Backup options}.
+Make a backup of each file that would otherwise be overwritten or removed.
+
+@item -c
+@opindex -c
+Ignored; for compatibility with old Unix versions of @code{install}.
+
+@item -d
+@itemx --directory
+@opindex -d
+@opindex --directory
+@cindex directories, creating with given attributes
+@cindex parent directories, creating missing
+@cindex leading directories, creating missing
+Create each given directory and any missing parent directories, setting
+the owner, group and mode as given on the command line or to the
+defaults. It also gives any parent directories it creates those
+attributes. (This is different from the SunOS 4.x @code{install}, which
+gives directories that it creates the default attributes.)
+
+@item -g @var{group}
+@itemx --group=@var{group}
+@opindex -g
+@opindex --group
+@cindex group ownership of installed files, setting
+Set the group ownership of installed files or directories to
+@var{group}. The default is the process' current group. @var{group}
+may be either a group name or a numeric group id.
+
+@item -m @var{mode}
+@itemx --mode=@var{mode}
+@opindex -m
+@opindex --mode
+@cindex permissions of installed files, setting
+Set the permissions for the installed file or directory to @var{mode},
+which can be either an octal number, or a symbolic mode as in
+@code{chmod}, with 0 as the point of departure (@pxref{File
+permissions}). The default mode is @samp{u=rwx,go=rx}---read, write,
+and execute for the owner, and read and execute for group and other.
+
+@item -o @var{owner}
+@itemx --owner=@var{owner}
+@opindex -o
+@opindex --owner
+@cindex ownership of installed files, setting
+@cindex appropriate privileges
+@vindex root @r{as default owner}
+If @code{install} has appropriate privileges (is run as root), set the
+ownership of installed files or directories to @var{owner}. The default
+is @code{root}. @var{owner} may be either a user name or a numeric user
+ID.
+
+@item -p
+@itemx --preserve-timestamps
+@opindex -p
+@opindex --preserve-timestamps
+@cindex timestamps of installed files, preserving
+Set the time of last access and the time of last modification of each
+installed file to match those of each corresponding original file.
+When a file is installed without this option, its last access and
+last modification times are both set to the time of installation.
+This option is useful if you want to use the last modification times
+of installed files to keep track of when they were last built as opposed
+to when they were last installed.
+
+@item -s
+@itemx --strip
+@opindex -s
+@opindex --strip
+@cindex symbol table information, stripping
+@cindex stripping symbol table information
+Strip the symbol tables from installed binary executables.
+
+@item -S @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -S
+@opindex --suffix
+Append @var{suffix} to each backup file made with @samp{-b}.
+@xref{Backup options}.
+
+@itemx @w{@kbd{--target-directory}=@var{directory}}
+@opindex --target-directory
+@cindex target directory
+@cindex destination directory
+Specify the destination @var{directory}.
+@xref{Target directory}.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before copying it.
+
+@item -V @var{method}
+@itemx --version-control=@var{method}
+@opindex -V
+@opindex --version-control
+Change the type of backups made with @samp{-b}. The @var{method}
+argument can be @samp{none} (or @samp{off}), @samp{numbered} (or
+@samp{t}), @samp{existing} (or @samp{nil}), or @samp{never} (or
+@samp{simple}). @xref{Backup options}.
+
+@end table
+
+
+@node mv invocation
+@section @code{mv}: Move (rename) files
+
+@pindex mv
+
+@code{mv} moves or renames files (or directories). Synopsis:
+
+@example
+mv [@var{option}]@dots{} @var{source} @var{dest}
+mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
+@end example
+
+If the last argument names an existing directory, @code{mv} moves each
+other given file into a file with the same name in that directory.
+Otherwise, if only two files are given, it renames the first as
+the second. It is an error if the last argument is not a directory
+and more than two files are given.
+
+@code{mv} can move any type of file from one filesystem to another.
+Prior to version @code{4.0} of the fileutils,
+@code{mv} could move only regular files between filesystems.
+For example, now @code{mv} can move an entire directory hierarchy
+including special device files from one partition to another. It first
+uses some of the same code that's used by @code{cp -a} to copy the
+requested directories and files, then (assuming the copy succeeded)
+it removes the originals. If the copy fails, then the part that was
+copied to the destination partition is removed. If you were to copy
+three directories from one partition to another and the copy of the first
+directory succeeded, but the second didn't, the first would be left on
+the destination partion and the second and third would be left on the
+original partition.
+
+@cindex prompting, and @code{mv}
+If a destination file exists but is normally unwritable, standard input
+is a terminal, and the @samp{-f} or @samp{--force} option is not given,
+@code{mv} prompts the user for whether to replace the file. (You might
+own the file, or have write permission on its directory.) If the
+response does not begin with @samp{y} or @samp{Y}, the file is skipped.
+
+@emph{Warning}: If you try to move a symlink that points to a directory,
+and you specify the symlink with a trailing slash, then @code{mv}
+doesn't move the symlink but instead moves the directory referenced
+by the symlink. @xref{Trailing slashes}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx @w{@kbd{--backup}[=@var{method}]}
+@opindex -b
+@opindex --backup
+@vindex VERSION_CONTROL
+@cindex backups, making
+@xref{Backup options}.
+Make a backup of each file that would otherwise be overwritten or removed.
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+@cindex prompts, omitting
+Do not prompt the user before removing an unwritable destination file.
+
+@item -i
+@itemx --interactive
+@opindex -i
+@opindex --interactive
+@cindex prompts, forcing
+Prompt whether to overwrite each existing destination file, regardless
+of its permissions. If the response does not begin with @samp{y} or
+@samp{Y}, the file is skipped.
+
+@item -u
+@itemx --update
+@opindex -u
+@opindex --update
+@cindex newer files, moving only
+Do not move a nondirectory that has an existing destination with the
+same or newer modification time.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before moving it.
+
+@itemx @w{@kbd{--strip-trailing-slashes}}
+@opindex --strip-trailing-slashes
+@cindex stripping trailing slashes
+Remove any trailing slashes from each @var{source} argument.
+@xref{Trailing slashes}.
+
+@item -S @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -S
+@opindex --suffix
+Append @var{suffix} to each backup file made with @samp{-b}.
+@xref{Backup options}.
+
+@itemx @w{@kbd{--target-directory}=@var{directory}}
+@opindex --target-directory
+@cindex target directory
+@cindex destination directory
+Specify the destination @var{directory}.
+@xref{Target directory}.
+
+@item -V @var{method}
+@itemx --version-control=@var{method}
+@opindex -V
+@opindex --version-control
+Change the type of backups made with @samp{-b}. The @var{method}
+argument can be @samp{none} (or @samp{off}), @samp{numbered} (or
+@samp{t}), @samp{existing} (or @samp{nil}), or @samp{never} (or
+@samp{simple}). @xref{Backup options}.
+
+@end table
+
+
+@node rm invocation
+@section @code{rm}: Remove files or directories
+
+@pindex rm
+@cindex removing files or directories
+
+@code{rm} removes each given @var{file}. By default, it does not remove
+directories. Synopsis:
+
+@example
+rm [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@cindex prompting, and @code{rm}
+If a file is unwritable, standard input is a terminal, and the @samp{-f}
+or @samp{--force} option is not given, or the @samp{-i} or
+@samp{--interactive} option @emph{is} given, @code{rm} prompts the user
+for whether to remove the file. If the response does not begin with
+@samp{y} or @samp{Y}, the file is skipped.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -d
+@itemx --directory
+@opindex -d
+@opindex --directory
+@cindex directories, removing with @code{unlink}
+@findex unlink
+@pindex fsck
+Attempt to remove directories with @code{unlink} instead of @code{rmdir}, and
+don't require a directory to be empty before trying to unlink it. This works
+only if you have appropriate privileges and if your operating system supports
+@code{unlink} for directories. Because unlinking a directory causes any files
+in the deleted directory to become unreferenced, it is wise to @code{fsck} the
+filesystem after doing this.
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+Ignore nonexistent files and never prompt the user.
+Ignore any previous @samp{--interactive} (@samp{-i}) option.
+
+@item -i
+@itemx --interactive
+@opindex -i
+@opindex --interactive
+Prompt whether to remove each file. If the response does not begin
+with @samp{y} or @samp{Y}, the file is skipped.
+Ignore any previous @samp{--force} (@samp{-f}) option.
+
+@item -r
+@itemx -R
+@itemx --recursive
+@opindex -r
+@opindex -R
+@opindex --recursive
+@cindex directories, removing (recursively)
+Remove the contents of directories recursively.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before removing it.
+
+@end table
+
+@cindex files beginning with @samp{-}, removing
+@cindex @samp{-}, removing files beginning with
+One common question is how to remove files whose names begin with a
+@samp{-}. @sc{gnu} @code{rm}, like every program that uses the @code{getopt}
+function to parse its arguments, lets you use the @samp{--} option to
+indicate that all following arguments are non-options. To remove a file
+called @file{-f} in the current directory, you could type either:
+
+@example
+rm -- -f
+@end example
+
+@noindent
+or:
+
+@example
+rm ./-f
+@end example
+
+@opindex - @r{and Unix @code{rm}}
+The Unix @code{rm} program's use of a single @samp{-} for this purpose
+predates the development of the getopt standard syntax.
+
+
+@node shred invocation
+@section @code{shred}: Remove files more securely
+
+@pindex shred
+@cindex data, erasing
+@cindex erasing data
+
+@code{shred} overwrites devices or files, to help prevent even
+very expensive hardware from recovering the data.
+
+Ordinarily when you remove a file (@pxref{rm invocation}), the data is
+not actually destroyed. Only the index listing where the file is
+stored is destroyed, and the storage is made available for reuse.
+There are undelete utilities that will attempt to reconstruct the index
+and can bring the file back if the parts were not reused.
+
+On a busy system with a nearly-full drive, space can get reused in a few
+seconds. But there is no way to know for sure. If you have sensitive
+data, you may want to be sure that recovery is not possible by actually
+overwriting the file with non-sensitive data.
+
+However, even after doing that, it is possible to take the disk back
+to a laboratory and use a lot of sensitive (and expensive) equipment
+to look for the faint ``echoes'' of the original data underneath the
+overwritten data. If the data has only been overwritten once, it's not
+even that hard.
+
+The best way to remove something irretrievably is to destroy the media
+it's on with acid, melt it down, or the like. For cheap removable media
+like floppy disks, this is the preferred method. However, hard drives
+are expensive and hard to melt, so the @code{shred} utility tries
+to achieve a similar effect non-destructively.
+
+This uses many overwrite passes, with the data patterns chosen to
+maximize the damage they do to the old data. While this will work on
+floppies, the patterns are designed for best effect on hard drives.
+For more details, see the source code and Peter Gutmann's paper
+@cite{Secure Deletion of Data from Magnetic and Solid-State Memory},
+from the proceedings of the Sixth USENIX Security Symposium (San Jose,
+California, 22--25 July, 1996). The paper is also available online
+@url{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html}.
+
+@strong{Please note} that @code{shred} relies on a very important assumption:
+that the filesystem overwrites data in place. This is the traditional
+way to do things, but many modern filesystem designs do not satisfy this
+assumption. Exceptions include:
+
+@itemize @bullet
+
+@item
+Log-structured or journaled filesystems, such as those supplied with
+AIX and Solaris.
+
+@item
+Filesystems that write redundant data and carry on even if some writes
+fail, such as RAID-based filesystems.
+
+@item
+Filesystems that make snapshots, such as Network Appliance's NFS server.
+
+@item
+Filesystems that cache in temporary locations, such as NFS version 3
+clients.
+
+@item
+Compressed filesystems.
+@end itemize
+
+If you are not sure how your filesystem operates, then you should assume
+that it does not overwrite data in place, which means that shred cannot
+reliably operate on regular files in your filesystem.
+
+Generally speaking, it is more reliable to shred a device than a file,
+since this bypasses the problem of filesystem design mentioned above.
+However, even shredding devices is not always completely reliable. For
+example, most disks map out bad sectors invisibly to the application; if
+the bad sectors contain sensitive data, @code{shred} won't be able to
+destroy it.
+
+@code{shred} makes no attempt to detect or report this problem, just as
+it makes no attempt to do anything about backups. However, since it is
+more reliable to shred devices than files, @code{shred} by default does
+not truncate or remove the output file. This default is more suitable
+for devices, which typically cannot be truncated and should not be
+removed.
+
+Finally, consider the risk of backups and mirrors.
+File system backups and remote mirrors may contain copies of the
+file that cannot be removed, and that will allow a shredded file
+to be recovered later. So if you keep any data you may later want
+to destroy using @code{shred}, be sure that it is not backed up or mirrored.
+
+@example
+shred [@var{option}]@dots{} @var{file}[@dots{}]
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+@cindex force deletion
+Override file permissions if necessary to allow overwriting.
+
+@item -@var{NUMBER}
+@itemx -n @var{NUMBER}
+@itemx --iterations=@var{NUMBER}
+@opindex -n @var{NUMBER}
+@opindex --iterations=@var{NUMBER}
+@cindex iterations, selecting the number of
+By default, @code{shred} uses 25 passes of overwrite. This is enough
+for all of the useful overwrite patterns to be used at least once.
+You can reduce this to save time, or increase it if you have a lot of
+time to waste.
+
+@item -s @var{BYTES}
+@itemx --size=@var{BYTES}
+@opindex -s @var{BYTES}
+@opindex --size=@var{BYTES}
+@cindex size of file to shred
+Shred the first @var{BYTES} bytes of the file. The default is to shred
+the whole file. @var{BYTES} can be followed by a size specification like
+@samp{k}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
+
+@item -u
+@itemx --remove
+@opindex -u
+@opindex --remove
+@cindex removing files after shredding
+After shredding a file, truncate it (if possible) and then remove it.
+If a file has multiple links, only the named links will be removed.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Display status updates as sterilization proceeds.
+
+@item -x
+@itemx --exact
+@opindex -x
+@opindex --exact
+Normally, shred rounds the file size up to the next multiple of
+the filesystem block size to fully erase the last block of the file.
+This option suppresses that behavior.
+Thus, by default if you shred a 10-byte file on a system with 512-byte
+blocks, the resulting file will be 512 bytes long. With this option,
+shred does not increase the size of the file.
+
+@item -z
+@itemx --zero
+@opindex -z
+@opindex --zero
+Normally, the last pass that @code{shred} writes is made up of
+random data. If this would be conspicuous on your hard drive (for
+example, because it looks like encrypted data), or you just think
+it's tidier, the @samp{--zero} option adds an additional overwrite pass with
+all zero bits. This is in addition to the number of passes specified
+by the @samp{--iterations} option.
+
+@item -
+@opindex -
+Shred standard output.
+
+This argument is considered an option. If the common @samp{--} option has
+been used to indicate the end of options on the command line, then @samp{-}
+will be interpreted as an ordinary file name.
+
+The intended use of this is to shred a removed temporary file.
+For example
+
+@example
+i=`tempfile -m 0600`
+exec 3<>"$i"
+rm -- "$i"
+echo "Hello, world" >&3
+shred - >&3
+exec 3>-
+@end example
+
+Note that the shell command @samp{shred - >file} does not shred the
+contents of @var{file}, since it truncates @var{file} before invoking
+@code{shred}. Use the command @samp{shred file} or (if using a
+Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
+
+@end table
+
+You might use the following command to erase all trace of the
+file system you'd created on the floppy disk in your first drive.
+That command takes about 20 minutes to erase a 1.44MB floppy.
+
+@example
+shred --verbose /dev/fd0
+@end example
+
+Similarly, to erase all data on a selected partition of
+your hard disk, you could give a command like this:
+
+@example
+shred --verbose /dev/sda5
+@end example
+
+@node Special file types
+@chapter Special file types
+
+@cindex special file types
+@cindex file types, special
+
+This chapter describes commands which create special types of files (and
+@code{rmdir}, which removes directories, one special file type).
+
+@cindex special file types
+@cindex file types
+Although Unix-like operating systems have markedly fewer special file
+types than others, not @emph{everything} can be treated only as the
+undifferentiated byte stream of @dfn{normal files}. For example, when a
+file is created or removed, the system must record this information,
+which it does in a @dfn{directory}---a special type of file. Although
+you can read directories as normal files, if you're curious, in order
+for the system to do its job it must impose a structure, a certain
+order, on the bytes of the file. Thus it is a ``special'' type of file.
+
+Besides directories, other special file types include named pipes
+(FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
+
+@menu
+* ln invocation:: Make links between files.
+* mkdir invocation:: Make directories.
+* mkfifo invocation:: Make FIFOs (named pipes).
+* mknod invocation:: Make block or character special files.
+* rmdir invocation:: Remove empty directories.
+@end menu
+
+
+@node ln invocation
+@section @code{ln}: Make links between files
+
+@pindex ln
+@cindex links, creating
+@cindex hard links, creating
+@cindex symbolic (soft) links, creating
+@cindex creating links (hard or soft)
+
+@cindex filesystems and hard links
+@code{ln} makes links between files. By default, it makes hard links;
+with the @samp{-s} option, it makes symbolic (or @dfn{soft}) links.
+Synopses:
+
+@example
+ln [@var{option}]@dots{} @var{target} [@var{linkname}]
+ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
+@end example
+
+@itemize @bullet
+
+@item If the last argument names an existing directory, @code{ln} creates a
+link to each @var{target} file in that directory, using the
+@var{target}s' names. (But see the description of the
+@samp{--no-dereference} option below.)
+
+@item If two filenames are given, @code{ln} creates a link from the
+second to the first.
+
+@item If one @var{target} is given, @code{ln} creates a link to that
+file in the current directory.
+
+@item It is an error if the last argument is not a directory and more
+than two files are given. Without @samp{-f} or @samp{-i} (see below),
+@code{ln} will not remove an existing file. Use the @samp{--backup}
+option to make @code{ln} rename existing files.
+
+@end itemize
+
+@cindex hard link, defined
+@cindex inode, and hard links
+A @dfn{hard link} is another name for an existing file; the link and the
+original are indistinguishable. Technically speaking, they share the
+same inode, and the inode contains all the information about a
+file---indeed, it is not incorrect to say that the inode @emph{is} the
+file. On all existing implementations, you cannot make a hard link to
+a directory, and hard links cannot cross filesystem boundaries. (These
+restrictions are not mandated by @sc{posix}, however.)
+
+@cindex dereferencing symbolic links
+@cindex symbolic link, defined
+@dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
+a special file type (which not all kernels support: System V release 3
+(and older) systems lack symlinks) in which the link file actually
+refers to a different file, by name. When most operations (opening,
+reading, writing, and so on) are passed the symbolic link file, the
+kernel automatically @dfn{dereferences} the link and operates on the
+target of the link. But some operations (e.g., removing) work on the
+link file itself, rather than on its target. @xref{Symbolic Links,,,
+library, The GNU C Library Reference Manual}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx @w{@kbd{--backup}[=@var{method}]}
+@opindex -b
+@opindex --backup
+@vindex VERSION_CONTROL
+@cindex backups, making
+@xref{Backup options}.
+Make a backup of each file that would otherwise be overwritten or removed.
+
+@item -d
+@itemx -F
+@itemx --directory
+@opindex -d
+@opindex -F
+@opindex --directory
+@cindex hard links to directories
+Allow the super-user to make hard links to directories.
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+Remove existing destination files.
+
+@item -i
+@itemx --interactive
+@opindex -i
+@opindex --interactive
+@cindex prompting, and @code{ln}
+Prompt whether to remove existing destination files.
+
+@item -n
+@itemx --no-dereference
+@opindex -n
+@opindex --no-dereference
+When given an explicit destination that is a symlink to a directory,
+treat that destination as if it were a normal file.
+
+When the destination is an actual directory (not a symlink to one),
+there is no ambiguity. The link is created in that directory.
+But when the specified destination is a symlink to a directory,
+there are two ways to treat the user's request. @code{ln} can
+treat the destination just as it would a normal directory and create
+the link in it. On the other hand, the destination can be viewed as a
+non-directory---as the symlink itself. In that case, @code{ln}
+must delete or backup that symlink before creating the new link.
+The default is to treat a destination that is a symlink to a directory
+just like a directory.
+
+@item -s
+@itemx --symbolic
+@opindex -s
+@opindex --symbolic
+Make symbolic links instead of hard links. This option merely produces
+an error message on systems that do not support symbolic links.
+
+@item -S @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -S
+@opindex --suffix
+Append @var{suffix} to each backup file made with @samp{-b}.
+@xref{Backup options}.
+
+@itemx @w{@kbd{--target-directory}=@var{directory}}
+@opindex --target-directory
+@cindex target directory
+@cindex destination directory
+Specify the destination @var{directory}.
+@xref{Target directory}.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before linking it.
+
+@item -V @var{method}
+@itemx --version-control=@var{method}
+@opindex -V
+@opindex --version-control
+Change the type of backups made with @samp{-b}. The @var{method}
+argument can be @samp{none} (or @samp{off}), @samp{numbered} (or
+@samp{t}), @samp{existing} (or @samp{nil}), or @samp{never} (or
+@samp{simple}). @xref{Backup options}.
+
+@end table
+
+Examples:
+
+@smallexample
+ln -s /some/name # creates link ./name pointing to /some/name
+ln -s /some/name myname # creates link ./myname pointing to /some/name
+ln -s a b .. # creates links ../a and ../b pointing to ./a and ./b
+@end smallexample
+
+
+@node mkdir invocation
+@section @code{mkdir}: Make directories
+
+@pindex mkdir
+@cindex directories, creating
+@cindex creating directories
+
+@code{mkdir} creates directories with the specified names. Synopsis:
+
+@example
+mkdir [@var{option}]@dots{} @var{name}@dots{}
+@end example
+
+If a @var{name} is an existing file but not a directory, @code{mkdir} prints a
+warning message on stderr and will exit with a status of 1 after
+processing any remaining @var{name}s. The same is done when a @var{name} is an
+existing directory and the -p option is not given. If a @var{name} is an
+existing directory and the -p option is given, @code{mkdir} will ignore it.
+That is, @code{mkdir} will not print a warning, raise an error, or change
+the mode of the directory (even if the -m option is given), and will
+move on to processing any remaining @var{name}s.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -m @var{mode}
+@itemx --mode=@var{mode}
+@opindex -m
+@opindex --mode
+@cindex modes of created directories, setting
+Set the mode of created directories to @var{mode}, which is symbolic as
+in @code{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
+everyone) minus the bits set in the umask for the point of the
+departure. @xref{File permissions}.
+
+@item -p
+@itemx --parents
+@opindex -p
+@opindex --parents
+@cindex parent directories, creating
+Make any missing parent directories for each argument. The mode for parent
+directories is set to the umask modified by @samp{u+wx}.
+Ignore arguments corresponding to existing directories.
+
+@item -v
+@item --verbose
+@opindex -v
+@opindex --verbose
+Print a message for each created directory. This is most useful with
+@samp{--parents}.
+@end table
+
+
+@node mkfifo invocation
+@section @code{mkfifo}: Make FIFOs (named pipes)
+
+@pindex mkfifo
+@cindex FIFOs, creating
+@cindex named pipes, creating
+@cindex creating FIFOs (named pipes)
+
+@code{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
+specified names. Synopsis:
+
+@example
+mkfifo [@var{option}] @var{name}@dots{}
+@end example
+
+A @dfn{FIFO} is a special file type that permits independent processes
+to communicate. One process opens the FIFO file for writing, and
+another for reading, after which data can flow as with the usual
+anonymous pipe in shells or elsewhere.
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+
+@item -m @var{mode}
+@itemx --mode=@var{mode}
+@opindex -m
+@opindex --mode
+@cindex modes of created FIFOs, setting
+Set the mode of created FIFOs to @var{mode}, which is symbolic as in
+@code{chmod} and uses @samp{a=rw} (read and write allowed for everyone) minus
+the bits set in the umask for the point of departure. @xref{File permissions}.
+
+@end table
+
+
+@node mknod invocation
+@section @code{mknod}: Make block or character special files
+
+@pindex mknod
+@cindex block special files, creating
+@cindex character special files, creating
+
+@code{mknod} creates a FIFO, character special file, or block special
+file with the specified name. Synopsis:
+
+@example
+mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
+@end example
+
+@cindex special files
+@cindex block special files
+@cindex character special files
+Unlike the phrase ``special file type'' above, the term @dfn{special
+file} has a technical meaning on Unix: something that can generate or
+receive data. Usually this corresponds to a physical piece of hardware,
+e.g., a printer or a disk. (These files are typically created at
+system-configuration time.) The @code{mknod} command is what creates
+files of this type. Such devices can be read either a character at a
+time or a ``block'' (many characters) at a time, hence we say there are
+@dfn{block special} files and @dfn{character special} files.
+
+The arguments after @var{name} specify the type of file to make:
+
+@table @samp
+
+@item p
+@opindex p @r{for FIFO file}
+for a FIFO
+
+@item b
+@opindex b @r{for block special file}
+for a block special file
+
+@item c
+@c Don't document the `u' option -- it's just a synonym for `c'.
+@c Do *any* versions of mknod still use it?
+@c @itemx u
+@opindex c @r{for character special file}
+@c @opindex u @r{for character special file}
+for a character special file
+
+@end table
+
+When making a block or character special file, the major and minor
+device numbers must be given after the file type.
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+
+@item -m @var{mode}
+@itemx --mode=@var{mode}
+@opindex -m
+@opindex --mode
+Set the mode of created files to @var{mode}, which is symbolic as in
+@code{chmod} and uses @samp{a=rw} minus the bits set in the umask as the point
+of departure. @xref{File permissions}.
+
+@end table
+
+
+@node rmdir invocation
+@section @code{rmdir}: Remove empty directories
+
+@pindex rmdir
+@cindex removing empty directories
+@cindex directories, removing empty
+
+@code{rmdir} removes empty directories. Synopsis:
+
+@example
+rmdir [@var{option}]@dots{} @var{directory}@dots{}
+@end example
+
+If any @var{directory} argument does not refer to an existing empty
+directory, it is an error.
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+
+@item --ignore-fail-on-non-empty
+@opindex --ignore-fail-on-non-empty
+@cindex directory deletion, ignoring failures
+Ignore each failure to remove a directory that is solely because
+the directory is non-empty.
+
+@item -p
+@itemx --parents
+@opindex -p
+@opindex --parents
+@cindex parent directories, removing
+Remove @var{directory}, then try to remove each component of @var{directory}.
+So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
+As such, it fails if any of those directories turns out not to be empty.
+Use the @samp{--ignore-fail-on-non-empty} option to make it so such
+a failure does not evoke a diagnostic and does not cause @code{rmdir} to
+exit unsuccessfully.
+
+@item -v
+@item --verbose
+@opindex -v
+@opindex --verbose
+@cindex directory deletion, reporting
+Give a diagnostic for each successful removal.
+@var{directory} is removed.
+
+@end table
+
+@xref{rm invocation}, for how to remove non-empty directories (recursively).
+
+
+@node Changing file attributes
+@chapter Changing file attributes
+
+@cindex changing file attributes
+@cindex file attributes, changing
+@cindex attributes, file
+
+A file is not merely its contents, a name, and a file type
+(@pxref{Special file types}). A file also has an owner (a userid), a
+group (a group id), permissions (what the owner can do with the file,
+what people in the group can do, and what everyone else can do), various
+timestamps, and other information. Collectively, we call these a file's
+@dfn{attributes}.
+
+These commands change file attributes.
+
+@menu
+* chown invocation:: Change file owners and groups.
+* chgrp invocation:: Change file groups.
+* chmod invocation:: Change access permissions.
+* touch invocation:: Change file timestamps.
+@end menu
+
+
+@node chown invocation
+@section @code{chown}: Change file owner and group
+
+@pindex chown
+@cindex file ownership, changing
+@cindex group ownership, changing
+@cindex changing file ownership
+@cindex changing group ownership
+
+@code{chown} changes the user and/or group ownership of each given @var{file}
+to @var{new-owner} or to the user and group of an existing reference file.
+Synopsis:
+
+@example
+chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
+@end example
+
+If used, @var{new-owner} specifies the new owner and/or group as follows
+(with no embedded white space):
+
+@example
+[@var{owner}] [ [:] [@var{group}] ]
+@end example
+
+Specifically:
+
+@table @var
+@item owner
+If only an @var{owner} (a user name or numeric user id) is given, that
+user is made the owner of each given file, and the files' group is not
+changed.
+
+@itemx owner@samp{:}group
+If the @var{owner} is followed by a colon and a @var{group} (a
+group name or numeric group id), with no spaces between them, the group
+ownership of the files is changed as well (to @var{group}).
+
+@itemx owner@samp{:}
+If a colon but no group name follows @var{owner}, that user is
+made the owner of the files and the group of the files is changed to
+@var{owner}'s login group.
+
+@itemx @samp{:}group
+If the colon and following @var{group} are given, but the owner
+is omitted, only the group of the files is changed; in this case,
+@code{chown} performs the same function as @code{chgrp}.
+
+@end table
+
+You may use @samp{.} in place of the @samp{:} separator. This is a
+@sc{gnu} extension for compatibility with older scripts.
+New scripts should avoid the use of @samp{.} because @sc{gnu} @code{chown}
+may fail if @var{owner} contains @samp{.} characters.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --changes
+@opindex -c
+@opindex --changes
+@cindex changed owners, verbosely describing
+Verbosely describe the action for each @var{file} whose ownership
+actually changes.
+
+@item -f
+@itemx --silent
+@itemx --quiet
+@opindex -f
+@opindex --silent
+@opindex --quiet
+@cindex error messages, omitting
+Do not print error messages about files whose ownership cannot be
+changed.
+
+@itemx @w{@kbd{--from}=@var{old-owner}}
+@opindex --from
+@cindex symbolic links, changing owner
+Change a @var{file}'s ownership only if it has current attributes specified
+by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
+described above.
+This option is useful primarily from a security standpoint in that
+it narrows considerably the window of potential abuse.
+For example, to reflect a UID numbering change for one user's files
+without an option like this, @code{root} might run
+
+@smallexample
+find / -owner OLDUSER -print0 | xargs -0 chown NEWUSER
+@end smallexample
+
+But that is dangerous because the interval between when the @code{find}
+tests the existing file's owner and when the @code{chown} is actually run
+may be quite large.
+One way to narrow the gap would be to invoke chown for each file
+as it is found:
+
+@example
+find / -owner OLDUSER -exec chown NEWUSER @{@} \;
+@end example
+
+But that is very slow if there are many affected files.
+With this option, it is safer (the gap is narrower still)
+though still not perfect:
+
+@example
+chown -R --from=OLDUSER NEWUSER /
+@end example
+
+@item --dereference
+@opindex --dereference
+@cindex symbolic links, changing owner
+@findex lchown
+Do not act on symbolic links themselves but rather on what they point to.
+
+@item -h
+@itemx --no-dereference
+@opindex -h
+@opindex --no-dereference
+@cindex symbolic links, changing owner
+@findex lchown
+Act on symbolic links themselves instead of what they point to.
+This is the default.
+This mode relies on the @code{lchown} system call.
+On systems that do not provide the @code{lchown} system call,
+@code{chown} fails when a file specified on the command line
+is a symbolic link.
+By default, no diagnostic is issued for symbolic links encountered
+during a recursive traversal, but see @samp{--verbose}.
+
+@item --reference=@var{ref_file}
+@opindex --reference
+Change the user and group of each @var{file} to be the same as those of
+@var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
+user and group of the symbolic link, but rather those of the file it
+refers to.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Output a diagnostic for every file processed.
+If a symbolic link is encountered during a recursive traversal
+on a system without the @code{lchown} system call, and @samp{--no-dereference}
+is in effect, then issue a diagnostic saying neither the symbolic link nor
+its referent is being changed.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+@cindex recursively changing file ownership
+Recursively change ownership of directories and their contents.
+
+@end table
+
+
+@node chgrp invocation
+@section @code{chgrp}: Change group ownership
+
+@pindex chgrp
+@cindex group ownership, changing
+@cindex changing group ownership
+
+@code{chgrp} changes the group ownership of each given @var{file}
+to @var{group} (which can be either a group name or a numeric group id)
+or to the group of an existing reference file. Synopsis:
+
+@example
+chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --changes
+@opindex -c
+@opindex --changes
+@cindex changed files, verbosely describing
+Verbosely describe the action for each @var{file} whose group actually
+changes.
+
+@item -f
+@itemx --silent
+@itemx --quiet
+@opindex -f
+@opindex --silent
+@opindex --quiet
+@cindex error messages, omitting
+Do not print error messages about files whose group cannot be
+changed.
+
+@item --dereference
+@opindex --dereference
+@cindex symbolic links, changing owner
+@findex lchown
+Do not act on symbolic links themselves but rather on what they point to.
+
+@item -h
+@itemx --no-dereference
+@opindex -h
+@opindex --no-dereference
+@cindex symbolic links, changing group
+@findex lchown
+Act on symbolic links themselves instead of what they point to.
+This is the default.
+This mode relies on the @code{lchown} system call.
+On systems that do not provide the @code{lchown} system call,
+@code{chgrp} fails when a file specified on the command line
+is a symbolic link.
+By default, no diagnostic is issued for symbolic links encountered
+during a recursive traversal, but see @samp{--verbose}.
+
+@item --reference=@var{ref_file}
+@opindex --reference
+Change the group of each @var{file} to be the same as that of
+@var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
+group of the symbolic link, but rather that of the file it refers to.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Output a diagnostic for every file processed.
+If a symbolic link is encountered during a recursive traversal
+on a system without the @code{lchown} system call, and @samp{--no-dereference}
+is in effect, then issue a diagnostic saying neither the symbolic link nor
+its referent is being changed.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+@cindex recursively changing group ownership
+Recursively change the group ownership of directories and their contents.
+
+@end table
+
+
+@node chmod invocation
+@section @code{chmod}: Change access permissions
+
+@pindex chmod
+@cindex changing access permissions
+@cindex access permissions, changing
+@cindex permissions, changing access
+
+@code{chmod} changes the access permissions of the named files. Synopsis:
+
+@example
+chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
+@end example
+
+@cindex symbolic links, permissions of
+@code{chmod} never changes the permissions of symbolic links, since
+the @code{chmod} system call cannot change their permissions.
+This is not a problem since the permissions of symbolic links are
+never used. However, for each symbolic link listed on the command
+line, @code{chmod} changes the permissions of the pointed-to file.
+In contrast, @code{chmod} ignores symbolic links encountered during
+recursive directory traversals.
+
+If used, @var{mode} specifies the new permissions.
+For details, see the section on @ref{File permissions}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --changes
+@opindex -c
+@opindex --changes
+Verbosely describe the action for each @var{file} whose permissions
+actually changes.
+
+@item -f
+@itemx --silent
+@itemx --quiet
+@opindex -f
+@opindex --silent
+@opindex --quiet
+@cindex error messages, omitting
+Do not print error messages about files whose permissions cannot be
+changed.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Verbosely describe the action or non-action taken for every @var{file}.
+
+@item --reference=@var{ref_file}
+@opindex --reference
+Change the mode of each @var{file} to be the same as that of @var{ref_file}.
+@xref{File permissions}.
+If @var{ref_file} is a symbolic link, do not use the mode
+of the symbolic link, but rather that of the file it refers to.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+@cindex recursively changing access permissions
+Recursively change permissions of directories and their contents.
+
+@end table
+
+
+@node touch invocation
+@section @code{touch}: Change file timestamps
+
+@pindex touch
+@cindex changing file timestamps
+@cindex file timestamps, changing
+@cindex timestamps, changing file
+
+@code{touch} changes the access and/or modification times of the
+specified files. Synopsis:
+
+@example
+touch [@var{option}]@dots{} @var{file}@dots{}
+@end example
+
+If the first @var{file} would be a valid argument to the @samp{-t}
+option and no timestamp is given with any of the @samp{-d}, @samp{-r},
+or @samp{-t} options and the @samp{--} argument is not given, that
+argument is interpreted as the time for the other files instead of
+as a file name. Warning: this usage is obsolescent, and future versions
+of @sc{posix} will require that support for it be withdrawn. Use
+@option{-t} instead.
+
+@cindex empty files, creating
+Any @var{file} that does not exist is created empty.
+
+@cindex permissions, for changing file timestamps
+If changing both the access and modification times to the current
+time, @code{touch} can change the timestamps for files that the user
+running it does not own but has write permission for. Otherwise, the
+user must own the files.
+
+Although @code{touch} provides options for changing two of the times --
+the times of last access and modification -- of a file, there is actually
+a third one as well: the inode change time. This is often referred to
+as a file's @code{ctime}.
+The inode change time represents the time when the file's meta-information
+last changed. One common example of this is when the permissions of a
+file change. Changing the permissions doesn't access the file, so
+the atime doesn't change, nor does it modify the file, so the mtime
+doesn't change. Yet, something about the file itself has changed,
+and this must be noted somewhere. This is the job of the ctime field.
+This is necessary, so that, for example, a backup program can make a
+fresh copy of the file, including the new permissions value.
+Another operation that modifies a file's ctime without affecting
+the others is renaming. In any case, it is not possible, in normal
+operations, for a user to change the ctime field to a user-specified value.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --time=atime
+@itemx --time=access
+@itemx --time=use
+@opindex -a
+@opindex --time
+@opindex atime@r{, changing}
+@opindex access @r{time, changing}
+@opindex use @r{time, changing}
+Change the access time only.
+
+@item -c
+@itemx --no-create
+@opindex -c
+@opindex --no-create
+Do not create files that do not exist.
+
+@item -d
+@itemx --date=time
+@opindex -d
+@opindex --date
+@opindex time
+Use @var{time} instead of the current time. It can contain month names,
+time zones, @samp{am} and @samp{pm}, etc. @xref{Date input formats}.
+
+@item -f
+@opindex -f
+@cindex BSD @code{touch} compatibility
+Ignored; for compatibility with BSD versions of @code{touch}.
+
+@item -m
+@itemx --time=mtime
+@itemx --time=modify
+@opindex -m
+@opindex --time
+@opindex mtime@r{, changing}
+@opindex modify @r{time, changing}
+Change the modification time only.
+
+@item -r @var{file}
+@itemx --reference=@var{file}
+@opindex -r
+@opindex --reference
+Use the times of the reference @var{file} instead of the current time.
+
+@item -t [[CC]YY]MMDDhhmm[.ss]
+Use the argument (optional four-digit or two-digit years, months,
+days, hours, minutes, optional seconds) instead of the current time.
+If the year is specified with only two digits, then @var{CC}
+is 20 for years in the range 0 @dots{} 68, and 19 for years in
+69 @dots{} 99. If no digits of the year are specified,
+the argument is interpreted as a date in the current year.
+
+@end table
+
+
+@node Disk usage
+@chapter Disk usage
+
+@cindex disk usage
+
+No disk can hold an infinite amount of data. These commands report on
+how much disk storage is in use or available. (This has nothing much to
+do with how much @emph{main memory}, i.e., RAM, a program is using when
+it runs; for that, you want @code{ps} or @code{pstat} or @code{swap}
+or some such command.)
+
+@menu
+* df invocation:: Report filesystem disk space usage.
+* du invocation:: Estimate file space usage.
+* sync invocation:: Synchronize memory and disk.
+@end menu
+
+
+@node df invocation
+@section @code{df}: Report filesystem disk space usage
+
+@pindex df
+@cindex filesystem disk usage
+@cindex disk usage by filesystem
+
+@code{df} reports the amount of disk space used and available on
+filesystems. Synopsis:
+
+@example
+df [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+With no arguments, @code{df} reports the space used and available on all
+currently mounted filesystems (of all types). Otherwise, @code{df}
+reports on the filesystem containing each argument @var{file}.
+
+Normally the disk space is printed in units of
+1024 bytes, but this can be overridden (@pxref{Block size}).
+
+@cindex disk device file
+@cindex device file, disk
+If an argument @var{file} is a disk device file containing a mounted
+filesystem, @code{df} shows the space available on that filesystem
+rather than on the filesystem containing the device node (i.e., the root
+filesystem). @sc{gnu} @code{df} does not attempt to determine the disk usage
+on unmounted filesystems, because on most kinds of systems doing so
+requires extremely nonportable intimate knowledge of filesystem
+structures.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+@cindex automounter filesystems
+@cindex ignore filesystems
+Include in the listing filesystems that have a size of 0 blocks, which
+are omitted by default. Such filesystems are typically special-purpose
+pseudo-filesystems, such as automounter entries. Also, filesystems of
+type ``ignore'' or ``auto'', supported by some operating systems, are
+only included if this option is specified.
+
+@item -h
+@itemx --human-readable
+@opindex -h
+@opindex --human-readable
+@cindex human-readable output
+Append a size letter such as @samp{M} for megabytes to each size.
+Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
+Use the @samp{-H} or @samp{--si} option if you prefer powers of 1000.
+
+@item -H
+@itemx --si
+@opindex -H
+@opindex --si
+@cindex SI output
+Append a size letter such as @samp{M} for megabytes to each size. (SI
+is the International System of Units, which defines these letters as
+prefixes.) Powers of 1000 are used, not 1024; @samp{M} stands for
+1,000,000 bytes. Use the @samp{-h} or @samp{--human-readable} option if
+you prefer powers of 1024.
+
+@item -i
+@itemx --inodes
+@opindex -i
+@opindex --inodes
+@cindex inode usage
+List inode usage information instead of block usage. An inode (short
+for index node) contains information about a file such as its owner,
+permissions, timestamps, and location on the disk.
+
+@item -k
+@itemx --kilobytes
+@opindex -k
+@opindex --kilobytes
+@cindex kilobytes for filesystem sizes
+Print sizes in 1024-byte blocks, overriding the default block size
+(@pxref{Block size}).
+
+@item -l
+@itemx --local
+@opindex -l
+@opindex --local
+@cindex filesystem types, limiting output to certain
+Limit the listing to local filesystems. By default, remote filesystems
+are also listed.
+
+@item -m
+@itemx --megabytes
+@opindex -m
+@opindex --megabytes
+@cindex megabytes for filesystem sizes
+Print sizes in megabyte (that is, 1,048,576-byte) blocks.
+
+@item --no-sync
+@opindex --no-sync
+@cindex filesystem space, retrieving old data more quickly
+Do not invoke the @code{sync} system call before getting any usage data.
+This may make @code{df} run significantly faster on systems with many
+disks, but on some systems (notably SunOS) the results may be slightly
+out of date. This is the default.
+
+@item -P
+@itemx --portability
+@opindex -P
+@opindex --portability
+@cindex one-line output format
+@cindex @sc{posix} output format
+@cindex portable output format
+@cindex output format, portable
+Use the @sc{posix} output format. This is like the default format except
+for the following:
+
+@enumerate
+@item
+The information about each filesystem is always printed on exactly
+one line; a mount device is never put on a line by itself. This means
+that if the mount device name is more than 20 characters long (e.g., for
+some network mounts), the columns are misaligned.
+
+@item
+Non-integer values are rounded up, instead of being rounded down or
+rounded to the nearest integer.
+
+@item
+The labels in the header output line are changed to conform to @sc{posix}.
+@end enumerate
+
+@item --sync
+@opindex --sync
+@cindex filesystem space, retrieving current data more slowly
+Invoke the @code{sync} system call before getting any usage data. On
+some systems (notably SunOS), doing this yields more up to date results,
+but in general this option makes @code{df} much slower, especially when
+there are many or very busy filesystems.
+
+@item -t @var{fstype}
+@itemx --type=@var{fstype}
+@opindex -t
+@opindex --type
+@cindex filesystem types, limiting output to certain
+Limit the listing to filesystems of type @var{fstype}. Multiple
+filesystem types can be specified by giving multiple @samp{-t} options.
+By default, nothing is omitted.
+
+@item -T
+@itemx --print-type
+@opindex -T
+@opindex --print-type
+@cindex filesystem types, printing
+Print each filesystem's type. The types printed here are the same ones
+you can include or exclude with @samp{-t} and @samp{-x}. The particular
+types printed are whatever is supported by the system. Here are some of
+the common names (this list is certainly not exhaustive):
+
+@table @samp
+
+@item nfs
+@cindex NFS filesystem type
+An NFS filesystem, i.e., one mounted over a network from another
+machine. This is the one type name which seems to be used uniformly by
+all systems.
+
+@item 4.2@r{, }ufs@r{, }efs@dots{}
+@cindex Linux filesystem types
+@cindex local filesystem types
+@opindex 4.2 @r{filesystem type}
+@opindex ufs @r{filesystem type}
+@opindex efs @r{filesystem type}
+A filesystem on a locally-mounted hard disk. (The system might even
+support more than one type here; Linux does.)
+
+@item hsfs@r{, }cdfs
+@cindex CD-ROM filesystem type
+@cindex High Sierra filesystem
+@opindex hsfs @r{filesystem type}
+@opindex cdfs @r{filesystem type}
+A filesystem on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
+systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
+
+@item pcfs
+@cindex PC filesystem
+@cindex DOS filesystem
+@cindex MS-DOS filesystem
+@cindex diskette filesystem
+@opindex pcfs
+An MS-DOS filesystem, usually on a diskette.
+
+@end table
+
+@item -x @var{fstype}
+@itemx --exclude-type=@var{fstype}
+@opindex -x
+@opindex --exclude-type
+Limit the listing to filesystems not of type @var{fstype}.
+Multiple filesystem types can be eliminated by giving multiple
+@samp{-x} options. By default, no filesystem types are omitted.
+
+@item -v
+Ignored; for compatibility with System V versions of @code{df}.
+
+@end table
+
+
+@node du invocation
+@section @code{du}: Estimate file space usage
+
+@pindex du
+@cindex file space usage
+@cindex disk usage for files
+
+@code{du} reports the amount of disk space used by the specified files
+and for each subdirectory (of directory arguments). Synopsis:
+
+@example
+du [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+With no arguments, @code{du} reports the disk space for the current
+directory. Normally the disk space is printed in units of
+1024 bytes, but this can be overridden (@pxref{Block size}).
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Show counts for all files, not just directories.
+
+@item -b
+@itemx --bytes
+@opindex -b
+@opindex --bytes
+Print sizes in bytes, overriding the default block size (@pxref{Block size}).
+
+@item -c
+@itemx --total
+@opindex -c
+@opindex --total
+@cindex grand total of disk space
+Print a grand total of all arguments after all arguments have
+been processed. This can be used to find out the total disk usage of
+a given set of files or directories.
+
+@item -D
+@itemx --dereference-args
+@opindex -D
+@opindex --dereference-args
+Dereference symbolic links that are command line arguments.
+Does not affect other symbolic links. This is helpful for finding
+out the disk usage of directories, such as @file{/usr/tmp}, which
+are often symbolic links.
+
+@item -h
+@itemx --human-readable
+@opindex -h
+@opindex --human-readable
+@cindex human-readable output
+Append a size letter such as @samp{M} for megabytes to each size.
+Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
+Use the @samp{-H} or @samp{--si} option if you prefer powers of 1000.
+
+@item -H
+@itemx --si
+@opindex -H
+@opindex --si
+@cindex SI output
+Append a size letter such as @samp{M} for megabytes to each size. (SI
+is the International System of Units, which defines these letters as
+prefixes.) Powers of 1000 are used, not 1024; @samp{M} stands for
+1,000,000 bytes. Use the @samp{-h} or @samp{--human-readable} option if
+you prefer powers of 1024.
+
+@item -k
+@itemx --kilobytes
+@opindex -k
+@opindex --kilobytes
+Print sizes in 1024-byte blocks, overriding the default block size
+(@pxref{Block size}).
+
+@item -l
+@itemx --count-links
+@opindex -l
+@opindex --count-links
+@cindex hard links, counting in @code{du}
+Count the size of all files, even if they have appeared already (as a
+hard link).
+
+@item -L
+@itemx --dereference
+@opindex -L
+@opindex --dereference
+@cindex symbolic links, dereferencing in @code{du}
+Dereference symbolic links (show the disk space used by the file
+or directory that the link points to instead of the space used by
+the link).
+
+@item --max-depth=@var{DEPTH}
+@opindex --max-depth=@var{DEPTH}
+@cindex limiting output of @code{du}
+Show the total for each directory (and file if --all) that is at
+most MAX_DEPTH levels down from the root of the hierarchy. The root
+is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
+
+@item -m
+@itemx --megabytes
+@opindex -m
+@opindex --megabytes
+@cindex megabytes for filesystem sizes
+Print sizes in megabyte (that is, 1,048,576-byte) blocks.
+
+@item -s
+@itemx --summarize
+@opindex -s
+@opindex --summarize
+Display only a total for each argument.
+
+@item -S
+@itemx --separate-dirs
+@opindex -S
+@opindex --separate-dirs
+Report the size of each directory separately, not including the sizes
+of subdirectories.
+
+@item -x
+@itemx --one-file-system
+@opindex -x
+@opindex --one-file-system
+@cindex one filesystem, restricting @code{du} to
+Skip directories that are on different filesystems from the one that
+the argument being processed is on.
+
+@item --exclude=@var{PAT}
+@opindex --exclude=@var{PAT}
+@cindex excluding files from @code{du}
+When recursing, skip subdirectories or files matching @var{PAT}.
+For example, @code{du --exclude='*.o'} excludes files whose names
+end in @samp{.o}.
+
+@item -X @var{FILE}
+@itemx --exclude-from=@var{FILE}
+@opindex -X @var{FILE}
+@opindex --exclude-from=@var{FILE}
+@cindex excluding files from @code{du}
+Like @samp{--exclude}, except take the patterns to exclude from @var{FILE},
+one per line. If @var{FILE} is @samp{-}, take the patterns from standard
+input.
+
+@end table
+
+@cindex NFS mounts from BSD to HP-UX
+On BSD systems, @code{du} reports sizes that are half the correct
+values for files that are NFS-mounted from HP-UX systems. On HP-UX
+systems, it reports sizes that are twice the correct values for
+files that are NFS-mounted from BSD systems. This is due to a flaw
+in HP-UX; it also affects the HP-UX @code{du} program.
+
+
+@node sync invocation
+@section @code{sync}: Synchronize data on disk with memory
+
+@pindex sync
+@cindex synchronize disk and memory
+
+@cindex superblock, writing
+@cindex inodes, written buffered
+@code{sync} writes any data buffered in memory out to disk. This can
+include (but is not limited to) modified superblocks, modified inodes,
+and delayed reads and writes. This must be implemented by the kernel;
+The @code{sync} program does nothing but exercise the @code{sync} system
+call.
+
+@cindex crashes and corruption
+The kernel keeps data in memory to avoid doing (relatively slow) disk
+reads and writes. This improves performance, but if the computer
+crashes, data may be lost or the filesystem corrupted as a
+result. @code{sync} ensures everything in memory is written to disk.
+
+Any arguments are ignored, except for a lone @samp{--help} or
+@samp{--version} (@pxref{Common options}).
+
+@node Printing text
+@chapter Printing text
+
+@cindex printing text, commands for
+@cindex commands for printing text
+
+This section describes commands that display text strings.
+
+@menu
+* echo invocation:: Print a line of text.
+* printf invocation:: Format and print data.
+* yes invocation:: Print a string until interrupted.
+@end menu
+
+
+@node echo invocation
+@section @code{echo}: Print a line of text
+
+@pindex echo
+@cindex displaying text
+@cindex printing text
+@cindex text, displaying
+@cindex arbitrary text, displaying
+
+@code{echo} writes each given @var{string} to standard output, with a
+space between each and a newline after the last one. Synopsis:
+
+@example
+echo [@var{option}]@dots{} [@var{string}]@dots{}
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -n
+@opindex -n
+Do not output the trailing newline.
+
+@item -e
+@opindex -e
+@cindex backslash escapes
+Enable interpretation of the following backslash-escaped characters in
+each @var{string}:
+
+@table @samp
+@item \a
+alert (bell)
+@item \b
+backspace
+@item \c
+suppress trailing newline
+@item \f
+form feed
+@item \n
+new line
+@item \r
+carriage return
+@item \t
+horizontal tab
+@item \v
+vertical tab
+@item \\
+backslash
+@item \@var{nnn}
+the character whose ASCII code is @var{nnn} (octal); if @var{nnn} is not
+a valid octal number, it is printed literally.
+@end table
+
+@end table
+
+
+@node printf invocation
+@section @code{printf}: Format and print data
+
+@pindex printf
+@code{printf} does formatted printing of text. Synopsis:
+
+@example
+printf @var{format} [@var{argument}]@dots{}
+@end example
+
+@code{printf} prints the @var{format} string, interpreting @samp{%}
+directives and @samp{\} escapes in the same way as the C @code{printf}
+function. The @var{format} argument is re-used as necessary to convert
+all of the given @var{argument}s.
+
+@code{printf} has one additional directive, @samp{%b}, which prints its
+argument string with @samp{\} escapes interpreted in the same way as in
+the @var{format} string.
+
+@kindex \0ooo
+@kindex \0xhhh
+@code{printf} interprets @samp{\0ooo} in @var{format} as an octal number
+(if @var{ooo} is 0 to 3 octal digits) specifying a character to print,
+and @samp{\xhhh} as a hexadecimal number (if @var{hhh} is 1 to 3 hex
+digits) specifying a character to print.
+
+@kindex \uhhhh
+@kindex \Uhhhhhhhh
+@code{printf} interprets two character syntaxes introduced in ISO C 99:
+@samp{\u} for 16-bit Unicode characters, specified as 4 hex digits
+@var{hhhh}, and @samp{\U} for 32-bit Unicode characters, specified as 8 hex
+digits @var{hhhhhhhh}. @code{printf} outputs the Unicode characters
+according to the LC_CTYPE part of the current locale, i.e. depending
+on the values of the environment variables @code{LC_ALL}, @code{LC_CTYPE},
+@code{LANG}.
+
+The processing of @samp{\u} and @samp{\U} requires a full-featured
+@code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
+or when @code{libiconv} is installed prior to the sh-utils. Otherwise the
+use of @samp{\u} and @samp{\U} will give an error message.
+
+@kindex \c
+An additional escape, @samp{\c}, causes @code{printf} to produce no
+further output.
+
+The only options are a lone @samp{--help} or
+@samp{--version}. @xref{Common options}.
+
+The Unicode character syntaxes are useful for writing strings in a locale
+independent way. For example, a string containing the Euro currency symbol
+
+@example
+$ /usr/local/bin/printf '\u20AC 14.95'
+@end example
+
+@noindent
+will be output correctly in all locales supporting the Euro symbol
+(ISO-8859-15, UTF-8, and others). Similarly, a Chinese string
+
+@example
+$ /usr/local/bin/printf '\u4e2d\u6587'
+@end example
+
+@noindent
+will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
+
+Note that in these examples, the full pathname of @code{printf} has been
+given, to distinguish it from the GNU @code{bash} builtin function
+@code{printf}.
+
+For larger strings, you don't need to look up the hexadecimal code
+values of each character one by one. ASCII characters mixed with \u
+escape sequences is also known as the JAVA source file encoding. You can
+use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
+is how to convert a piece of text into a shell script which will output
+this text in a locale-independent way:
+
+@smallexample
+$ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
+ '\u4e2d\u6587\n' > sample.txt
+$ recode BIG5..JAVA < sample.txt \
+ | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
+ > sample.sh
+@end smallexample
+
+
+@node yes invocation
+@section @code{yes}: Print a string until interrupted
+
+@pindex yes
+@cindex repeated output of a string
+
+@code{yes} prints the command line arguments, separated by spaces and
+followed by a newline, forever until it is killed. If no arguments are
+given, it prints @samp{y} followed by a newline forever until killed.
+
+The only options are a lone @samp{--help} or @samp{--version}.
+@xref{Common options}.
+
+
+@node Conditions
+@chapter Conditions
+
+@cindex conditions
+@cindex commands for exit status
+@cindex exit status commands
+
+This section describes commands that are primarily useful for their exit
+status, rather than their output. Thus, they are often used as the
+condition of shell @code{if} statements, or as the last command in a
+pipeline.
+
+@menu
+* false invocation:: Do nothing, unsuccessfully.
+* true invocation:: Do nothing, successfully.
+* test invocation:: Check file types and compare values.
+* expr invocation:: Evaluate expressions.
+@end menu
+
+
+@node false invocation
+@section @code{false}: Do nothing, unsuccessfully
+
+@pindex false
+@cindex do nothing, unsuccessfully
+@cindex failure exit status
+@cindex exit status of @code{false}
+
+@code{false} does nothing except return an exit status of 1, meaning
+@dfn{failure}. It can be used as a place holder in shell scripts
+where an unsuccessful command is needed.
+
+By default, @code{false} honors the @samp{--help} and @samp{--version}
+options. However, that is contrary to @sc{posix}, so when the environment
+variable @env{POSIXLY_CORRECT} is set, @code{false} ignores @emph{all}
+command line arguments, including @samp{--help} and @samp{--version}.
+
+This version of @code{false} is implemented as a C program, and is thus
+more secure and faster than a shell script implementation, and may safely
+be used as a dummy shell for the purpose of disabling accounts.
+
+
+@node true invocation
+@section @code{true}: Do nothing, successfully
+
+@pindex true
+@cindex do nothing, successfully
+@cindex no-op
+@cindex successful exit
+@cindex exit status of @code{true}
+
+@code{true} does nothing except return an exit status of 0, meaning
+@dfn{success}. It can be used as a place holder in shell scripts
+where a successful command is needed, although the shell built-in
+command @code{:} (colon) may do the same thing faster.
+In most modern shells, @code{true} is a built-in command, so when
+you use @samp{true} in a script, you're probably using the built-in
+command, not the one documented here.
+
+By default, @code{true} honors the @samp{--help} and @samp{--version}
+options. However, that is contrary to @sc{posix}, so when the environment
+variable @env{POSIXLY_CORRECT} is set, @code{true} ignores @emph{all}
+command line arguments, including @samp{--help} and @samp{--version}.
+
+This version of @code{true} is implemented as a C program, and is thus
+more secure and faster than a shell script implementation, and may safely
+be used as a dummy shell for the purpose of disabling accounts.
+
+@node test invocation
+@section @code{test}: Check file types and compare values
+
+@pindex test
+@cindex check file types
+@cindex compare values
+@cindex expression evaluation
+
+@code{test} returns a status of 0 (true) or 1 (false) depending on the
+evaluation of the conditional expression @var{expr}. Each part of the
+expression must be a separate argument.
+
+@code{test} has file status checks, string operators, and numeric
+comparison operators.
+
+@cindex conflicts with shell built-ins
+@cindex built-in shell commands, conflicts with
+Because most shells have a built-in command by the same name, using the
+unadorned command name in a script or interactively may get you
+different functionality than that described here.
+
+Besides the options below, @code{test} accepts a lone @samp{--help} or
+@samp{--version}. @xref{Common options}. A single non-option argument
+is also allowed: @code{test} returns true if the argument is not null.
+
+@menu
+* File type tests:: -[bcdfhLpSt]
+* Access permission tests:: -[gkruwxOG]
+* File characteristic tests:: -e -s -nt -ot -ef
+* String tests:: -z -n = !=
+* Numeric tests:: -eq -ne -lt -le -gt -ge
+* Connectives for test:: ! -a -o
+@end menu
+
+
+@node File type tests
+@subsection File type tests
+
+@cindex file type tests
+
+These options test for particular types of files. (Everything's a file,
+but not all files are the same!)
+
+@table @samp
+
+@item -b @var{file}
+@opindex -b
+@cindex block special check
+True if @var{file} exists and is a block special device.
+
+@item -c @var{file}
+@opindex -c
+@cindex character special check
+True if @var{file} exists and is a character special device.
+
+@item -d @var{file}
+@opindex -d
+@cindex directory check
+True if @var{file} exists and is a directory.
+
+@item -f @var{file}
+@opindex -f
+@cindex regular file check
+True if @var{file} exists and is a regular file.
+
+@item -h @var{file}
+@itemx -L @var{file}
+@opindex -L
+@opindex -h
+@cindex symbolic link check
+True if @var{file} exists and is a symbolic link.
+
+@item -p @var{file}
+@opindex -p
+@cindex named pipe check
+True if @var{file} exists and is a named pipe.
+
+@item -S @var{file}
+@opindex -S
+@cindex socket check
+True if @var{file} exists and is a socket.
+
+@item -t [@var{fd}]
+@opindex -t
+@cindex terminal check
+True if @var{fd} is opened on a terminal. If @var{fd} is omitted, it
+defaults to 1 (standard output).
+
+@end table
+
+
+@node Access permission tests
+@subsection Access permission tests
+
+@cindex access permission tests
+@cindex permission tests
+
+These options test for particular access permissions.
+
+@table @samp
+
+@item -g @var{file}
+@opindex -g
+@cindex set-group-id check
+True if @var{file} exists and has its set-group-id bit set.
+
+@item -k @var{file}
+@opindex -k
+@cindex sticky bit check
+True if @var{file} has its @dfn{sticky} bit set.
+
+@item -r @var{file}
+@opindex -r
+@cindex readable file check
+True if @var{file} exists and is readable.
+
+@item -u @var{file}
+@opindex -u
+@cindex set-user-id check
+True if @var{file} exists and has its set-user-id bit set.
+
+@item -w @var{file}
+@opindex -w
+@cindex writable file check
+True if @var{file} exists and is writable.
+
+@item -x @var{file}
+@opindex -x
+@cindex executable file check
+True if @var{file} exists and is executable.
+
+@item -O @var{file}
+@opindex -O
+@cindex owned by effective uid check
+True if @var{file} exists and is owned by the current effective user id.
+
+@item -G @var{file}
+@opindex -G
+@cindex owned by effective gid check
+True if @var{file} exists and is owned by the current effective group id.
+
+@end table
+
+@node File characteristic tests
+@subsection File characteristic tests
+
+@cindex file characteristic tests
+
+These options test other file characteristics.
+
+@table @samp
+
+@item -e @var{file}
+@opindex -e
+@cindex existence-of-file check
+True if @var{file} exists.
+
+@item -s @var{file}
+@opindex -s
+@cindex nonempty file check
+True if @var{file} exists and has a size greater than zero.
+
+@item @var{file1} -nt @var{file2}
+@opindex -nt
+@cindex newer-than file check
+True if @var{file1} is newer (according to modification date) than
+@var{file2}.
+
+@item @var{file1} -ot @var{file2}
+@opindex -ot
+@cindex older-than file check
+True if @var{file1} is older (according to modification date) than
+@var{file2}.
+
+@item @var{file1} -ef @var{file2}
+@opindex -ef
+@cindex same file check
+@cindex hard link check
+True if @var{file1} and @var{file2} have the same device and inode
+numbers, i.e., if they are hard links to each other.
+
+@end table
+
+
+@node String tests
+@subsection String tests
+
+@cindex string tests
+
+These options test string characteristics. Strings are not quoted for
+@code{test}, though you may need to quote them to protect characters
+with special meaning to the shell, e.g., spaces.
+
+@table @samp
+
+@item -z @var{string}
+@opindex -z
+@cindex zero-length string check
+True if the length of @var{string} is zero.
+
+@item -n @var{string}
+@itemx @var{string}
+@opindex -n
+@cindex nonzero-length string check
+True if the length of @var{string} is nonzero.
+
+@item @var{string1} = @var{string2}
+@opindex =
+@cindex equal string check
+True if the strings are equal.
+
+@item @var{string1} != @var{string2}
+@opindex !=
+@cindex not-equal string check
+True if the strings are not equal.
+
+@end table
+
+
+@node Numeric tests
+@subsection Numeric tests
+
+@cindex numeric tests
+@cindex arithmetic tests
+
+Numeric relationals. The arguments must be entirely numeric (possibly
+negative), or the special expression @w{@code{-l @var{string}}}, which
+evaluates to the length of @var{string}.
+
+@table @samp
+
+@item @var{arg1} -eq @var{arg2}
+@itemx @var{arg1} -ne @var{arg2}
+@itemx @var{arg1} -lt @var{arg2}
+@itemx @var{arg1} -le @var{arg2}
+@itemx @var{arg1} -gt @var{arg2}
+@itemx @var{arg1} -ge @var{arg2}
+@opindex -eq
+@opindex -ne
+@opindex -lt
+@opindex -le
+@opindex -gt
+@opindex -ge
+These arithmetic binary operators return true if @var{arg1} is equal,
+not-equal, less-than, less-than-or-equal, greater-than, or
+greater-than-or-equal than @var{arg2}, respectively.
+
+@end table
+
+For example:
+
+@example
+test -1 -gt -2 && echo yes
+@result{} yes
+test -l abc -gt 1 && echo yes
+@result{} yes
+test 0x100 -eq 1
+@error{} test: integer expression expected before -eq
+@end example
+
+
+@node Connectives for test
+@subsection Connectives for @code{test}
+
+@cindex logical connectives
+@cindex connectives, logical
+
+The usual logical connectives.
+
+@table @samp
+
+@item ! @var{expr}
+@opindex !
+True if @var{expr} is false.
+
+@item @var{expr1} -a @var{expr2}
+@opindex -a
+@cindex logical and operator
+@cindex and operator
+True if both @var{expr1} and @var{expr2} are true.
+
+@item @var{expr1} -o @var{expr2}
+@opindex -o
+@cindex logical or operator
+@cindex or operator
+True if either @var{expr1} or @var{expr2} is true.
+
+@end table
+
+
+@node expr invocation
+@section @code{expr}: Evaluate expressions
+
+@pindex expr
+@cindex expression evaluation
+@cindex evaluation of expressions
+
+@code{expr} evaluates an expression and writes the result on standard
+output. Each token of the expression must be a separate argument.
+
+Operands are either numbers or strings. @code{expr} converts
+anything appearing in an operand position to an integer or a string
+depending on the operation being applied to it.
+
+Strings are not quoted for @code{expr} itself, though you may need to
+quote them to protect characters with special meaning to the shell,
+e.g., spaces.
+
+@cindex parentheses for grouping
+Operators may given as infix symbols or prefix keywords. Parentheses
+may be used for grouping in the usual manner (you must quote parentheses
+to avoid the shell evaluating them, however).
+
+@cindex exit status of @code{expr}
+Exit status:
+
+@display
+0 if the expression is neither null nor 0,
+1 if the expression is null or 0,
+2 for invalid expressions.
+@end display
+
+@menu
+* String expressions:: <colon> match substr index length quote
+* Numeric expressions:: + - * / %
+* Relations for expr:: | & < <= = == != >= >
+* Examples of expr:: Examples.
+@end menu
+
+
+@node String expressions
+@subsection String expressions
+
+@cindex string expressions
+@cindex expressions, string
+
+@code{expr} supports pattern matching and other string operators. These
+have lower precedence than both the numeric and relational operators (in
+the next sections).
+
+@table @samp
+
+@item @var{string} : @var{regex}
+@cindex pattern matching
+@cindex regular expression matching
+@cindex matching patterns
+Perform pattern matching. The arguments are converted to strings and the
+second is considered to be a (basic, a la GNU @code{grep}) regular
+expression, with a @code{^} implicitly prepended. The first argument is
+then matched against this regular expression.
+
+If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
+@code{:} expression returns the part of @var{string} that matched the
+subexpression; otherwise, it returns the number of characters matched.
+
+If the match fails, the @code{:} operator returns the null string if
+@samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
+
+@kindex \( @r{regexp operator}
+Only the first @samp{\( @dots{} \)} pair is relevant to the return
+value; additional pairs are meaningful only for grouping the regular
+expression operators.
+
+@kindex \+ @r{regexp operator}
+@kindex \? @r{regexp operator}
+@kindex \| @r{regexp operator}
+In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
+operators which respectively match one or more, zero or one, or separate
+alternatives. SunOS and other @code{expr}'s treat these as regular
+characters. (@sc{posix} allows either behavior.)
+@xref{Top, , Regular Expression Library, regex, Regex}, for details of
+regular expression syntax. Some examples are in @ref{Examples of expr}.
+
+@item match @var{string} @var{regex}
+@findex match
+An alternative way to do pattern matching. This is the same as
+@w{@samp{@var{string} : @var{regex}}}.
+
+@item substr @var{string} @var{position} @var{length}
+@findex substr
+Returns the substring of @var{string} beginning at @var{position}
+with length at most @var{length}. If either @var{position} or
+@var{length} is negative, zero, or non-numeric, returns the null string.
+
+@item index @var{string} @var{charset}
+@findex index
+Returns the first position in @var{string} where the first character in
+@var{charset} was found. If no character in @var{charset} is found in
+@var{string}, return 0.
+
+@item length @var{string}
+@findex length
+Returns the length of @var{string}.
+
+@item quote @var{token}
+@findex quote
+Interpret @var{token} as a string, even if it is a keyword like @var{match}
+or an operator like @code{/}.
+This makes it possible to test @code{expr length quote "$x"} or
+@code{expr quote "$x" : '.*/\(.\)'} and have it do the right thing even if
+the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
+This operator is a GNU extension. It is disabled when
+the environment variable @env{POSIXLY_CORRECT} is set.
+
+@end table
+
+To make @code{expr} interpret keywords as strings, you must use the
+@code{quote} operator.
+
+
+@node Numeric expressions
+@subsection Numeric expressions
+
+@cindex numeric expressions
+@cindex expressions, numeric
+
+@code{expr} supports the usual numeric operators, in order of increasing
+precedence. The string operators (previous section) have lower precedence,
+the connectives (next section) have higher.
+
+@table @samp
+
+@item + -
+@kindex +
+@kindex -
+@cindex addition
+@cindex subtraction
+Addition and subtraction. Both arguments are converted to numbers;
+an error occurs if this cannot be done.
+
+@item * / %
+@kindex *
+@kindex /
+@kindex %
+@cindex multiplication
+@cindex division
+@cindex remainder
+Multiplication, division, remainder. Both arguments are converted to
+numbers; an error occurs if this cannot be done.
+
+@end table
+
+
+@node Relations for expr
+@subsection Relations for @code{expr}
+
+@cindex connectives, logical
+@cindex logical connectives
+@cindex relations, numeric or string
+
+@code{expr} supports the usual logical connectives and relations. These
+are higher precedence than either the string or numeric operators
+(previous sections). Here is the list, lowest-precedence operator first.
+
+@table @samp
+
+@item |
+@kindex |
+@cindex logical or operator
+@cindex or operator
+Returns its first argument if that is neither null nor 0, otherwise its
+second argument.
+
+@item &
+@kindex &
+@cindex logical and operator
+@cindex and operator
+Return its first argument if neither argument is null or 0, otherwise
+0.
+
+@item < <= = == != >= >
+@kindex <
+@kindex <=
+@kindex =
+@kindex ==
+@kindex >
+@kindex >=
+@cindex comparison operators
+Compare the arguments and return 1 if the relation is true, 0 otherwise.
+@code{==} is a synonym for @code{=}. @code{expr} first tries to convert
+both arguments to numbers and do a numeric comparison; if either
+conversion fails, it does a lexicographic comparison.
+
+@end table
+
+
+@node Examples of expr
+@subsection Examples of using @code{expr}
+
+@cindex examples of @code{expr}
+Here are a few examples, including quoting for shell metacharacters.
+
+To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
+@example
+foo=`expr $foo + 1`
+@end example
+
+To print the non-directory part of the file name stored in
+@code{$fname}, which need not contain a @code{/}.
+@example
+expr $fname : '.*/\(^.*\)' '^|' $fname
+@end example
+
+An example showing that @code{\+} is an operator:
+@example
+expr aaa : 'a\+'
+@result{} 3
+@end example
+
+@example
+expr abc : 'a\(.\)c'
+@result{} b
+expr index abcdef cz
+@result{} 3
+expr index index a
+@error{} expr: syntax error
+expr index quote index a
+@result{} 0
+@end example
+
+
+@node Redirection
+@chapter Redirection
+
+@cindex redirection
+@cindex commands for redirection
+
+Unix shells commonly provide several forms of @dfn{redirection}---ways
+to change the input source or output destination of a command. But one
+useful redirection is performed by a separate command, not by the shell;
+it's described here.
+
+@menu
+* tee invocation:: Redirect output to multiple files.
+@end menu
+
+
+@node tee invocation
+@section @code{tee}: Redirect output to multiple files
+
+@pindex tee
+@cindex pipe fitting
+@cindex destinations, multiple output
+@cindex read from stdin and write to stdout and files
+
+The @code{tee} command copies standard input to standard output and also
+to any files given as arguments. This is useful when you want not only
+to send some data down a pipe, but also to save a copy. Synopsis:
+
+@example
+tee [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+If a file being written to does not already exist, it is created. If a
+file being written to already exists, the data it previously contained
+is overwritten unless the @code{-a} option is used.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -a
+@itemx --append
+@opindex -a
+@opindex --append
+Append standard input to the given files rather than overwriting
+them.
+
+@item -i
+@itemx --ignore-interrupts
+@opindex -i
+@opindex --ignore-interrupts
+Ignore interrupt signals.
+
+@end table
+
+
+@node File name manipulation
+@chapter File name manipulation
+
+@cindex file name manipulation
+@cindex manipulation of file names
+@cindex commands for file name manipulation
+
+This section describes commands that manipulate file names.
+
+@menu
+* basename invocation:: Strip directory and suffix from a file name.
+* dirname invocation:: Strip non-directory suffix from a file name.
+* pathchk invocation:: Check file name portability.
+@end menu
+
+
+@node basename invocation
+@section @code{basename}: Strip directory and suffix from a file name
+
+@pindex basename
+@cindex strip directory and suffix from file names
+@cindex directory, stripping from file names
+@cindex suffix, stripping from file names
+@cindex file names, stripping directory and suffix
+@cindex leading directory components, stripping
+
+@code{basename} removes any leading directory components from
+@var{name}. Synopsis:
+
+@example
+basename @var{name} [@var{suffix}]
+@end example
+
+If @var{suffix} is specified and is identical to the end of @var{name},
+it is removed from @var{name} as well. @code{basename} prints the
+result on standard output.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node dirname invocation
+@section @code{dirname}: Strip non-directory suffix from a file name
+
+@pindex dirname
+@cindex directory components, printing
+@cindex stripping non-directory suffix
+@cindex non-directory suffix, stripping
+
+@code{dirname} prints all but the final slash-delimited component of
+a string (presumably a filename). Synopsis:
+
+@example
+dirname @var{name}
+@end example
+
+If @var{name} is a single component, @code{dirname} prints @samp{.}
+(meaning the current directory).
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node pathchk invocation
+@section @code{pathchk}: Check file name portability
+
+@pindex pathchk
+@cindex file names, checking validity and portability
+@cindex valid file names, checking for
+@cindex portable file names, checking for
+
+@code{pathchk} checks portability of filenames. Synopsis:
+
+@example
+pathchk [@var{option}]@dots{} @var{name}@dots{}
+@end example
+
+For each @var{name}, @code{pathchk} prints a message if any of
+these conditions is true:
+@enumerate
+@item
+one of the existing directories in @var{name} does not have search
+(execute) permission,
+@item
+the length of @var{name} is larger than its filesystem's maximum
+file name length,
+@item
+the length of one component of @var{name}, corresponding to an
+existing directory name, is larger than its filesystem's maximum
+length for a file name component.
+@end enumerate
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+
+@item -p
+@itemx --portability
+@opindex -p
+@opindex --portability
+Instead of performing length checks on the underlying filesystem,
+test the length of each file name and its components against the
+@sc{posix.1} minimum limits for portability. Also check that the file
+name contains no characters not in the portable file name character set.
+
+@end table
+
+@cindex exit status of @code{pathchk}
+Exit status:
+
+@display
+0 if all specified file names passed all of the tests,
+1 otherwise.
+@end display
+
+
+@node Working context
+@chapter Working context
+
+@cindex working context
+@cindex commands for printing the working context
+
+This section describes commands that display or alter the context in
+which you are working: the current directory, the terminal settings, and
+so forth. See also the user-related commands in the next section.
+
+@menu
+* pwd invocation:: Print working directory.
+* stty invocation:: Print or change terminal characteristics.
+* printenv invocation:: Print environment variables.
+* tty invocation:: Print file name of terminal on standard input.
+@end menu
+
+
+@node pwd invocation
+@section @code{pwd}: Print working directory
+
+@pindex pwd
+@cindex print name of current directory
+@cindex current working directory, printing
+@cindex working directory, printing
+
+@cindex symbolic links and @code{pwd}
+@code{pwd} prints the fully resolved name of the current directory.
+That is, all components of the printed name will be actual directory
+names---none will be symbolic links.
+
+@cindex conflicts with shell built-ins
+@cindex built-in shell commands, conflicts with
+Because most shells have a built-in command by the same name, using the
+unadorned command name in a script or interactively may get you
+different functionality than that described here.
+
+The only options are a lone @samp{--help} or
+@samp{--version}. @xref{Common options}.
+
+
+@node stty invocation
+@section @code{stty}: Print or change terminal characteristics
+
+@pindex stty
+@cindex change or print terminal settings
+@cindex terminal settings
+@cindex line settings of terminal
+
+@code{stty} prints or changes terminal characteristics, such as baud rate.
+Synopses:
+
+@example
+stty [@var{option}] [@var{setting}]@dots{}
+stty [@var{option}]
+@end example
+
+If given no line settings, @code{stty} prints the baud rate, line
+discipline number (on systems that support it), and line settings
+that have been changed from the values set by @samp{stty sane}.
+By default, mode reading and setting are performed on the tty line
+connected to standard input, although this can be modified by the
+@samp{--file} option.
+
+@code{stty} accepts many non-option arguments that change aspects of
+the terminal line operation, as described below.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Print all current settings in human-readable form. This option may not
+be used in combination with any line settings.
+
+@item -F @var{device}
+@itemx --file=@var{device}
+@opindex -F
+@opindex --file
+Set the line opened by the filename specified in @var{device} instead of
+the tty line connected to standard input. This option is necessary
+because opening a @sc{posix} tty requires use of the @code{O_NONDELAY} flag to
+prevent a @sc{posix} tty from blocking until the carrier detect line is high if
+the @code{clocal} flag is not set. Hence, it is not always possible
+to allow the shell to open the device in the traditional manner.
+
+@item -g
+@itemx --save
+@opindex -g
+@opindex --save
+@cindex machine-readable @code{stty} output
+Print all current settings in a form that can be used as an argument to
+another @code{stty} command to restore the current settings. This option
+may not be used in combination with any line settings.
+
+@end table
+
+Many settings can be turned off by preceding them with a @samp{-}.
+Such arguments are marked below with ``May be negated'' in their
+description. The descriptions themselves refer to the positive
+case, that is, when @emph{not} negated (unless stated otherwise,
+of course).
+
+Some settings are not available on all @sc{posix} systems, since they use
+extensions. Such arguments are marked below with ``Non-@sc{posix}'' in their
+description. On non-@sc{posix} systems, those or other settings also may not
+be available, but it's not feasible to document all the variations: just
+try it and see.
+
+@menu
+* Control:: Control settings
+* Input:: Input settings
+* Output:: Output settings
+* Local:: Local settings
+* Combination:: Combination settings
+* Characters:: Special characters
+* Special:: Special settings
+@end menu
+
+
+@node Control
+@subsection Control settings
+
+@cindex control settings
+Control settings:
+
+@table @samp
+@item parenb
+@opindex parenb
+@cindex two-way parity
+Generate parity bit in output and expect parity bit in input.
+May be negated.
+
+@item parodd
+@opindex parodd
+@cindex odd parity
+@cindex even parity
+Set odd parity (even if negated). May be negated.
+
+@item cs5
+@itemx cs6
+@itemx cs7
+@itemx cs8
+@opindex cs@var{n}
+@cindex character size
+@cindex eight-bit characters
+Set character size to 5, 6, 7, or 8 bits.
+
+@item hup
+@itemx hupcl
+@opindex hup[cl]
+Send a hangup signal when the last process closes the tty. May be
+negated.
+
+@item cstopb
+@opindex cstopb
+@cindex stop bits
+Use two stop bits per character (one if negated). May be negated.
+
+@item cread
+@opindex cread
+Allow input to be received. May be negated.
+
+@item clocal
+@opindex clocal
+@cindex modem control
+Disable modem control signals. May be negated.
+
+@item crtscts
+@opindex crtscts
+@cindex hardware flow control
+@cindex flow control, hardware
+@cindex RTS/CTS flow control
+Enable RTS/CTS flow control. Non-@sc{posix}. May be negated.
+@end table
+
+
+@node Input
+@subsection Input settings
+
+@cindex input settings
+
+@table @samp
+@item ignbrk
+@opindex ignbrk
+@cindex breaks, ignoring
+Ignore break characters. May be negated.
+
+@item brkint
+@opindex brkint
+@cindex breaks, cause interrupts
+Make breaks cause an interrupt signal. May be negated.
+
+@item ignpar
+@opindex ignpar
+@cindex parity, ignoring
+Ignore characters with parity errors. May be negated.
+
+@item parmrk
+@opindex parmrk
+@cindex parity errors, marking
+Mark parity errors (with a 255-0-character sequence). May be negated.
+
+@item inpck
+@opindex inpck
+Enable input parity checking. May be negated.
+
+@item istrip
+@opindex istrip
+@cindex eight-bit input
+Clear high (8th) bit of input characters. May be negated.
+
+@item inlcr
+@opindex inlcr
+@cindex newline, translating to return
+Translate newline to carriage return. May be negated.
+
+@item igncr
+@opindex igncr
+@cindex return, ignoring
+Ignore carriage return. May be negated.
+
+@item icrnl
+@opindex icrnl
+@cindex return, translating to newline
+Translate carriage return to newline. May be negated.
+
+@item ixon
+@opindex ixon
+@kindex C-s/C-q flow control
+@cindex XON/XOFF flow control
+Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
+be negated.
+
+@item ixoff
+@itemx tandem
+@opindex ixoff
+@opindex tandem
+@cindex software flow control
+@cindex flow control, software
+Enable sending of @code{stop} character when the system input buffer
+is almost full, and @code{start} character when it becomes almost
+empty again. May be negated.
+
+@item iuclc
+@opindex iuclc
+@cindex uppercase, translating to lowercase
+Translate uppercase characters to lowercase. Non-@sc{posix}. May be
+negated.
+
+@item ixany
+@opindex ixany
+Allow any character to restart output (only the start character
+if negated). Non-@sc{posix}. May be negated.
+
+@item imaxbel
+@opindex imaxbel
+@cindex beeping at input buffer full
+Enable beeping and not flushing input buffer if a character arrives
+when the input buffer is full. Non-@sc{posix}. May be negated.
+@end table
+
+
+@node Output
+@subsection Output settings
+
+@cindex output settings
+These arguments specify output-related operations.
+
+@table @samp
+@item opost
+@opindex opost
+Postprocess output. May be negated.
+
+@item olcuc
+@opindex olcuc
+@cindex lowercase, translating to output
+Translate lowercase characters to uppercase. Non-@sc{posix}. May be
+negated.
+
+@item ocrnl
+@opindex ocrnl
+@cindex return, translating to newline
+Translate carriage return to newline. Non-@sc{posix}. May be negated.
+
+@item onlcr
+@opindex onlcr
+@cindex newline, translating to crlf
+Translate newline to carriage return-newline. Non-@sc{posix}. May be
+negated.
+
+@item onocr
+@opindex onocr
+Do not print carriage returns in the first column. Non-@sc{posix}.
+May be negated.
+
+@item onlret
+@opindex onlret
+Newline performs a carriage return. Non-@sc{posix}. May be negated.
+
+@item ofill
+@opindex ofill
+@cindex pad instead of timing for delaying
+Use fill (padding) characters instead of timing for delays. Non-@sc{posix}.
+May be negated.
+
+@item ofdel
+@opindex ofdel
+@cindex pad character
+Use delete characters for fill instead of null characters. Non-@sc{posix}.
+May be negated.
+
+@item nl1
+@itemx nl0
+@opindex nl@var{n}
+Newline delay style. Non-@sc{posix}.
+
+@item cr3
+@itemx cr2
+@itemx cr1
+@itemx cr0
+@opindex cr@var{n}
+Carriage return delay style. Non-@sc{posix}.
+
+@item tab3
+@itemx tab2
+@itemx tab1
+@itemx tab0
+@opindex tab@var{n}
+Horizontal tab delay style. Non-@sc{posix}.
+
+@item bs1
+@itemx bs0
+@opindex bs@var{n}
+Backspace delay style. Non-@sc{posix}.
+
+@item vt1
+@itemx vt0
+@opindex vt@var{n}
+Vertical tab delay style. Non-@sc{posix}.
+
+@item ff1
+@itemx ff0
+@opindex ff@var{n}
+Form feed delay style. Non-@sc{posix}.
+@end table
+
+
+@node Local
+@subsection Local settings
+
+@cindex local settings
+
+@table @samp
+@item isig
+@opindex isig
+Enable @code{interrupt}, @code{quit}, and @code{suspend} special
+characters. May be negated.
+
+@item icanon
+@opindex icanon
+Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
+special characters. May be negated.
+
+@item iexten
+@opindex iexten
+Enable non-@sc{posix} special characters. May be negated.
+
+@item echo
+@opindex echo
+Echo input characters. May be negated.
+
+@item echoe
+@itemx crterase
+@opindex echoe
+@opindex crterase
+Echo @code{erase} characters as backspace-space-backspace. May be
+negated.
+
+@item echok
+@opindex echok
+@cindex newline echoing after @code{kill}
+Echo a newline after a @code{kill} character. May be negated.
+
+@item echonl
+@opindex echonl
+@cindex newline, echoing
+Echo newline even if not echoing other characters. May be negated.
+
+@item noflsh
+@opindex noflsh
+@cindex flushing, disabling
+Disable flushing after @code{interrupt} and @code{quit} special
+characters. May be negated.
+
+@item xcase
+@opindex xcase
+@cindex case translation
+Enable input and output of uppercase characters by preceding their
+lowercase equivalents with @samp{\}, when @code{icanon} is set.
+Non-@sc{posix}. May be negated.
+
+@item tostop
+@opindex tostop
+@cindex background jobs, stopping at terminal write
+Stop background jobs that try to write to the terminal. Non-@sc{posix}.
+May be negated.
+
+@item echoprt
+@itemx prterase
+@opindex echoprt
+@opindex prterase
+Echo erased characters backward, between @samp{\} and @samp{/}.
+Non-@sc{posix}. May be negated.
+
+@item echoctl
+@itemx ctlecho
+@opindex echoctl
+@opindex ctlecho
+@cindex control characters, using @samp{^@var{c}}
+@cindex hat notation for control characters
+Echo control characters in hat notation (@samp{^@var{c}}) instead
+of literally. Non-@sc{posix}. May be negated.
+
+@item echoke
+@itemx crtkill
+@opindex echoke
+@opindex crtkill
+Echo the @code{kill} special character by erasing each character on
+the line as indicated by the @code{echoprt} and @code{echoe} settings,
+instead of by the @code{echoctl} and @code{echok} settings. Non-@sc{posix}.
+May be negated.
+@end table
+
+
+@node Combination
+@subsection Combination settings
+
+@cindex combination settings
+Combination settings:
+
+@table @samp
+@item evenp
+@opindex evenp
+@itemx parity
+@opindex parity
+Same as @code{parenb -parodd cs7}. May be negated. If negated, same
+as @code{-parenb cs8}.
+
+@item oddp
+@opindex oddp
+Same as @code{parenb parodd cs7}. May be negated. If negated, same
+as @code{-parenb cs8}.
+
+@item nl
+@opindex nl
+Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
+@code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
+
+@item ek
+@opindex ek
+Reset the @code{erase} and @code{kill} special characters to their default
+values.
+
+@item sane
+@opindex sane
+Same as:
+@c This is too long to write inline.
+@example
+cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
+-iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
+-onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
+ff0 isig icanon iexten echo echoe echok -echonl
+-noflsh -xcase -tostop -echoprt echoctl echoke
+@end example
+@noindent and also sets all special characters to their default values.
+
+@item cooked
+@opindex cooked
+Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
+sets the @code{eof} and @code{eol} characters to their default values
+if they are the same as the @code{min} and @code{time} characters.
+May be negated. If negated, same as @code{raw}.
+
+@item raw
+@opindex raw
+Same as:
+@example
+-ignbrk -brkint -ignpar -parmrk -inpck -istrip
+-inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
+-imaxbel -opost -isig -icanon -xcase min 1 time 0
+@end example
+@noindent May be negated. If negated, same as @code{cooked}.
+
+@item cbreak
+@opindex cbreak
+Same as @code{-icanon}. May be negated. If negated, same as
+@code{icanon}.
+
+@item pass8
+@opindex pass8
+@cindex eight-bit characters
+Same as @code{-parenb -istrip cs8}. May be negated. If negated,
+same as @code{parenb istrip cs7}.
+
+@item litout
+@opindex litout
+Same as @code{-parenb -istrip -opost cs8}. May be negated.
+If negated, same as @code{parenb istrip opost cs7}.
+
+@item decctlq
+@opindex decctlq
+Same as @code{-ixany}. Non-@sc{posix}. May be negated.
+
+@item tabs
+@opindex tabs
+Same as @code{tab0}. Non-@sc{posix}. May be negated. If negated, same
+as @code{tab3}.
+
+@item lcase
+@itemx LCASE
+@opindex lcase
+@opindex LCASE
+Same as @code{xcase iuclc olcuc}. Non-@sc{posix}. May be negated.
+
+@item crt
+@opindex crt
+Same as @code{echoe echoctl echoke}.
+
+@item dec
+@opindex dec
+Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
+@end table
+
+
+@node Characters
+@subsection Special characters
+
+@cindex special characters
+@cindex characters, special
+
+The special characters' default values vary from system to system.
+They are set with the syntax @samp{name value}, where the names are
+listed below and the value can be given either literally, in hat
+notation (@samp{^@var{c}}), or as an integer which may start with
+@samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
+any other digit to indicate decimal.
+
+@cindex disabling special characters
+@kindex u@r{, and disabling special characters}
+For GNU stty, giving a value of @code{^-} or @code{undef} disables that
+special character. (This is incompatible with Ultrix @code{stty},
+which uses a value of @samp{u} to disable a special character. GNU
+@code{stty} treats a value @samp{u} like any other, namely to set that
+special character to @key{U}.)
+
+@table @samp
+
+@item intr
+@opindex intr
+Send an interrupt signal.
+
+@item quit
+@opindex quit
+Send a quit signal.
+
+@item erase
+@opindex erase
+Erase the last character typed.
+
+@item kill
+@opindex kill
+Erase the current line.
+
+@item eof
+@opindex eof
+Send an end of file (terminate the input).
+
+@item eol
+@opindex eol
+End the line.
+
+@item eol2
+@opindex eol2
+Alternate character to end the line. Non-@sc{posix}.
+
+@item swtch
+@opindex swtch
+Switch to a different shell layer. Non-@sc{posix}.
+
+@item start
+@opindex start
+Restart the output after stopping it.
+
+@item stop
+@opindex stop
+Stop the output.
+
+@item susp
+@opindex susp
+Send a terminal stop signal.
+
+@item dsusp
+@opindex dsusp
+Send a terminal stop signal after flushing the input. Non-@sc{posix}.
+
+@item rprnt
+@opindex rprnt
+Redraw the current line. Non-@sc{posix}.
+
+@item werase
+@opindex werase
+Erase the last word typed. Non-@sc{posix}.
+
+@item lnext
+@opindex lnext
+Enter the next character typed literally, even if it is a special
+character. Non-@sc{posix}.
+@end table
+
+
+@node Special
+@subsection Special settings
+
+@cindex special settings
+
+@table @samp
+@item min @var{n}
+@opindex min
+Set the minimum number of characters that will satisfy a read until
+the time value has expired, when @code{-icanon} is set.
+
+@item time @var{n}
+@opindex time
+Set the number of tenths of a second before reads time out if the minimum
+number of characters have not been read, when @code{-icanon} is set.
+
+@item ispeed @var{n}
+@opindex ispeed
+Set the input speed to @var{n}.
+
+@item ospeed @var{n}
+@opindex ospeed
+Set the output speed to @var{n}.
+
+@item rows @var{n}
+@opindex rows
+Tell the tty kernel driver that the terminal has @var{n} rows. Non-@sc{posix}.
+
+@item cols @var{n}
+@itemx columns @var{n}
+@opindex cols
+@opindex columns
+Tell the kernel that the terminal has @var{n} columns. Non-@sc{posix}.
+
+@item size
+@opindex size
+@vindex LINES
+@vindex COLUMNS
+Print the number of rows and columns that the kernel thinks the
+terminal has. (Systems that don't support rows and columns in the kernel
+typically use the environment variables @env{LINES} and @env{COLUMNS}
+instead; however, GNU @code{stty} does not know anything about them.)
+Non-@sc{posix}.
+
+@item line @var{n}
+@opindex line
+Use line discipline @var{n}. Non-@sc{posix}.
+
+@item speed
+@opindex speed
+Print the terminal speed.
+
+@item @var{n}
+@cindex baud rate, setting
+@c FIXME: Is this still true that the baud rate can't be set
+@c higher than 38400?
+Set the input and output speeds to @var{n}. @var{n} can be one
+of: 0 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600
+19200 38400 @code{exta} @code{extb}. @code{exta} is the same as
+19200; @code{extb} is the same as 38400. 0 hangs up the line if
+@code{-clocal} is set.
+@end table
+
+
+@node printenv invocation
+@section @code{printenv}: Print all or some environment variables
+
+@pindex printenv
+@cindex printing all or some environment variables
+@cindex environment variables, printing
+
+@code{printenv} prints environment variable values. Synopsis:
+
+@example
+printenv [@var{option}] [@var{variable}]@dots{}
+@end example
+
+If no @var{variable}s are specified, @code{printenv} prints the value of
+every environment variable. Otherwise, it prints the value of each
+@var{variable} that is set, and nothing for those that are not set.
+
+The only options are a lone @samp{--help} or @samp{--version}.
+@xref{Common options}.
+
+@cindex exit status of @code{printenv}
+Exit status:
+
+@display
+0 if all variables specified were found
+1 if at least one specified variable was not found
+2 if a write error occurred
+@end display
+
+
+@node tty invocation
+@section @code{tty}: Print file name of terminal on standard input
+
+@pindex tty
+@cindex print terminal file name
+@cindex terminal file name, printing
+
+@code{tty} prints the file name of the terminal connected to its standard
+input. It prints @samp{not a tty} if standard input is not a terminal.
+Synopsis:
+
+@example
+tty [@var{option}]@dots{}
+@end example
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+
+@item -s
+@itemx --silent
+@itemx --quiet
+@opindex -s
+@opindex --silent
+@opindex --quiet
+Print nothing; only return an exit status.
+
+@end table
+
+@cindex exit status of @code{tty}
+Exit status:
+
+@display
+0 if standard input is a terminal
+1 if standard input is not a terminal
+2 if given incorrect arguments
+3 if a write error occurs
+@end display
+
+
+@node User information
+@chapter User information
+
+@cindex user information, commands for
+@cindex commands for printing user information
+
+This section describes commands that print user-related information:
+logins, groups, and so forth.
+
+@menu
+* id invocation:: Print real and effective uid and gid.
+* logname invocation:: Print current login name.
+* whoami invocation:: Print effective user id.
+* groups invocation:: Print group names a user is in.
+* users invocation:: Print login names of users currently logged in.
+* who invocation:: Print who is currently logged in.
+@end menu
+
+
+@node id invocation
+@section @code{id}: Print real and effective uid and gid
+
+@pindex id
+@cindex real uid and gid, printing
+@cindex effective uid and gid, printing
+@cindex printing real and effective uid and gid
+
+@code{id} prints information about the given user, or the process
+running it if no user is specified. Synopsis:
+
+@example
+id [@var{option}]@dots{} [@var{username}]
+@end example
+
+By default, it prints the real user id, real group id, effective user id
+if different from the real user id, effective group id if different from
+the real group id, and supplemental group ids.
+
+Each of these numeric values is preceded by an identifying string and
+followed by the corresponding user or group name in parentheses.
+
+The options cause @code{id} to print only part of the above information.
+Also see @ref{Common options}.
+
+@table @samp
+@item -g
+@itemx --group
+@opindex -g
+@opindex --group
+Print only the group id.
+
+@item -G
+@itemx --groups
+@opindex -G
+@opindex --groups
+Print only the supplementary groups.
+
+@item -n
+@itemx --name
+@opindex -n
+@opindex --name
+Print the user or group name instead of the ID number. Requires
+@code{-u}, @code{-g}, or @code{-G}.
+
+@item -r
+@itemx --real
+@opindex -r
+@opindex --real
+Print the real, instead of effective, user or group id. Requires
+@code{-u}, @code{-g}, or @code{-G}.
+
+@item -u
+@itemx --user
+@opindex -u
+@opindex --user
+Print only the user id.
+
+@end table
+
+
+@node logname invocation
+@section @code{logname}: Print current login name
+
+@pindex logname
+@cindex printing user's login name
+@cindex login name, printing
+@cindex user name, printing
+
+@flindex /etc/utmp
+@flindex utmp
+
+@code{logname} prints the calling user's name, as found in the file
+@file{/etc/utmp}, and exits with a status of 0. If there is no
+@file{/etc/utmp} entry for the calling process, @code{logname} prints
+an error message and exits with a status of 1.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node whoami invocation
+@section @code{whoami}: Print effective user id
+
+@pindex whoami
+@cindex effective UID, printing
+@cindex printing the effective UID
+
+@code{whoami} prints the user name associated with the current
+effective user id. It is equivalent to the command @samp{id -un}.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node groups invocation
+@section @code{groups}: Print group names a user is in
+
+@pindex groups
+@cindex printing groups a user is in
+@cindex supplementary groups, printing
+
+@code{groups} prints the names of the primary and any supplementary
+groups for each given @var{username}, or the current process if no names
+are given. If names are given, the name of each user is printed before
+the list of that user's groups. Synopsis:
+
+@example
+groups [@var{username}]@dots{}
+@end example
+
+The group lists are equivalent to the output of the command @samp{id -Gn}.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node users invocation
+@section @code{users}: Print login names of users currently logged in
+
+@pindex users
+@cindex printing current usernames
+@cindex usernames, printing current
+
+@cindex login sessions, printing users with
+@code{users} prints on a single line a blank-separated list of user
+names of users currently logged in to the current host. Each user name
+corresponds to a login session, so if a user has more than one login
+session, that user's name will appear the same number of times in the
+output. Synopsis:
+
+@example
+users [@var{file}]
+@end example
+
+@flindex /etc/utmp
+@flindex /etc/wtmp
+With no @var{file} argument, @code{users} extracts its information from
+the file @file{/etc/utmp}. If a file argument is given, @code{users}
+uses that file instead. A common choice is @file{/etc/wtmp}.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node who invocation
+@section @code{who}: Print who is currently logged in
+
+@pindex who
+@cindex printing current user information
+@cindex information, about current users
+
+@code{who} prints information about users who are currently logged on.
+Synopsis:
+
+@example
+@code{who} [@var{option}] [@var{file}] [am i]
+@end example
+
+@cindex terminal lines, currently used
+@cindex login time
+@cindex remote hostname
+If given no non-option arguments, @code{who} prints the following
+information for each user currently logged on: login name, terminal
+line, login time, and remote hostname or X display.
+
+@flindex /etc/utmp
+@flindex /etc/wtmp
+If given one non-option argument, @code{who} uses that instead of
+@file{/etc/utmp} as the name of the file containing the record of
+users logged on. @file{/etc/wtmp} is commonly given as an argument
+to @code{who} to look at who has previously logged on.
+
+@opindex am i
+@opindex who am i
+If given two non-option arguments, @code{who} prints only the entry
+for the user running it (determined from its standard input), preceded
+by the hostname. Traditionally, the two arguments given are @samp{am
+i}, as in @samp{who am i}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -m
+@opindex -m
+Same as @samp{who am i}.
+
+@item -q
+@itemx --count
+@opindex -q
+@opindex --count
+Print only the login names and the number of users logged on.
+Overrides all other options.
+
+@item -s
+@opindex -s
+Ignored; for compatibility with other versions of @code{who}.
+
+@item -i
+@itemx -u
+@itemx --idle
+@opindex -i
+@opindex -u
+@opindex --idle
+@cindex idle time
+After the login time, print the number of hours and minutes that the
+user has been idle. @samp{.} means the user was active in last minute.
+@samp{old} means the user was idle for more than 24 hours.
+
+@item -l
+@itemx --lookup
+@opindex -l
+@opindex --lookup
+Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
+is not the default because it can cause significant delays on systems with
+automatic dial-up internet access.
+
+@item -H
+@itemx --heading
+@opindex -H
+@opindex --heading
+Print a line of column headings.
+
+@item -w
+@itemx -T
+@itemx --mesg
+@itemx --message
+@itemx --writable
+@opindex -w
+@opindex -T
+@opindex --mesg
+@opindex --message
+@opindex --writable
+@cindex message status
+@pindex write@r{, allowed}
+After each login name print a character indicating the user's message status:
+
+@display
+@samp{+} allowing @code{write} messages
+@samp{-} disallowing @code{write} messages
+@samp{?} cannot find terminal device
+@end display
+
+@end table
+
+
+@node System context
+@chapter System context
+
+@cindex system context
+@cindex context, system
+@cindex commands for system context
+
+This section describes commands that print or change system-wide
+information.
+
+@menu
+* date invocation:: Print or set system date and time.
+* uname invocation:: Print system information.
+* hostname invocation:: Print or set system name.
+* hostid invocation:: Print numeric host identifier.
+@end menu
+
+
+@node date invocation
+@section @code{date}: Print or set system date and time
+
+@pindex date
+@cindex time, printing or setting
+@cindex printing the current time
+
+Synopses:
+
+@example
+date [@var{option}]@dots{} [+@var{format}]
+date [-u|--utc|--universal] @c this avoids a newline in the output
+[ MMDDhhmm[[CC]YY][.ss] ]
+@end example
+
+Invoking @code{date} with no @var{format} argument is equivalent to invoking
+@samp{date '+%a %b %e %H:%M:%S %Z %Y'}.
+
+@findex strftime @r{and @code{date}}
+@cindex time formats
+@cindex formatting times
+If given an argument that starts with a @samp{+}, @code{date} prints the
+current time and date (or the time and date specified by the
+@code{--date} option, see below) in the format defined by that argument,
+which is the same as in the @code{strftime} function. Except for
+directives, which start with @samp{%}, characters in the format string
+are printed unchanged. The directives are described below.
+
+@menu
+* Time directives:: %[HIklMprsSTXzZ]
+* Date directives:: %[aAbBcdDhjmUwWxyY]
+* Literal directives:: %[%nt]
+* Padding:: Pad with zeroes, spaces (%_), or nothing (%-).
+* Setting the time:: Changing the system clock.
+* Options for date:: Instead of the current time.
+* Examples of date:: Examples.
+@end menu
+
+@node Time directives
+@subsection Time directives
+
+@cindex time directives
+@cindex directives, time
+
+@code{date} directives related to times.
+
+@table @samp
+@item %H
+hour (00@dots{}23)
+@item %I
+hour (01@dots{}12)
+@item %k
+hour ( 0@dots{}23)
+@item %l
+hour ( 1@dots{}12)
+@item %M
+minute (00@dots{}59)
+@item %p
+locale's AM or PM
+@item %r
+time, 12-hour (hh:mm:ss [AP]M)
+@item %s
+@cindex epoch, seconds since
+@cindex seconds since the epoch
+@cindex beginning of time
+seconds since the epoch, i.e., 1 January 1970 00:00:00 UTC (a
+GNU extension).
+Note that this value is the number of seconds between the epoch
+and the current date as defined by the localtime system call.
+It isn't changed by the @samp{--date} option.
+@item %S
+second (00@dots{}60)
+@item %T
+time, 24-hour (hh:mm:ss)
+@item %X
+locale's time representation (%H:%M:%S)
+@item %z
+RFC-822 style numeric time zone (e.g., -0600 or +0100), or nothing if no
+time zone is determinable. This value reflects the @emph{current} time
+zone. It isn't changed by the @samp{--date} option.
+@item %Z
+time zone (e.g., EDT), or nothing if no time zone is
+determinable.
+Note that this value reflects the @emph{current} time zone.
+It isn't changed by the @samp{--date} option.
+@end table
+
+
+@node Date directives
+@subsection Date directives
+
+@cindex date directives
+@cindex directives, date
+
+@code{date} directives related to dates.
+
+@table @samp
+@item %a
+locale's abbreviated weekday name (Sun@dots{}Sat)
+@item %A
+locale's full weekday name, variable length (Sunday@dots{}Saturday)
+@item %b
+locale's abbreviated month name (Jan@dots{}Dec)
+@item %B
+locale's full month name, variable length (January@dots{}December)
+@item %c
+locale's date and time (Sat Nov 04 12:02:33 EST 1989)
+@item %C
+century (year divided by 100 and truncated to an integer) (00@dots{}99)
+@item %d
+day of month (01@dots{}31)
+@item %D
+date (mm/dd/yy)
+@item %h
+same as %b
+@item %j
+day of year (001@dots{}366)
+@item %m
+month (01@dots{}12)
+@item %U
+week number of year with Sunday as first day of week (00@dots{}53).
+Days in a new year preceding the first Sunday are in week zero.
+@item %V
+week number of year with Monday as first day of the week as a decimal
+(01@dots{}53). If the week containing January 1 has four or more days in
+the new year, then it is considered week 1; otherwise, it is week 53 of
+the previous year, and the next week is week 1. (See the ISO 8601: 1988
+standard.)
+@item %w
+day of week (0@dots{}6) with 0 corresponding to Sunday
+@item %W
+week number of year with Monday as first day of week (00@dots{}53).
+Days in a new year preceding the first Monday are in week zero.
+@item %x
+locale's date representation (mm/dd/yy)
+@item %y
+last two digits of year (00@dots{}99)
+@item %Y
+year (1970@dots{}.)
+@end table
+
+
+@node Literal directives
+@subsection Literal directives
+
+@cindex literal directives
+@cindex directives, literal
+
+@code{date} directives that produce literal strings.
+
+@table @samp
+@item %%
+a literal %
+@item %n
+a newline
+@item %t
+a horizontal tab
+@end table
+
+
+@node Padding
+@subsection Padding
+
+@cindex numeric field padding
+@cindex padding of numeric fields
+@cindex fields, padding numeric
+
+By default, @code{date} pads numeric fields with zeroes, so that, for
+example, numeric months are always output as two digits. GNU @code{date}
+recognizes the following numeric modifiers between the @samp{%} and the
+directive.
+
+@table @samp
+@item -
+(hyphen) do not pad the field; useful if the output is intended for
+human consumption.
+@item _
+(underscore) pad the field with spaces; useful if you need a fixed
+number of characters in the output, but zeroes are too distracting.
+@end table
+
+@noindent
+These are GNU extensions.
+
+Here is an example illustrating the differences:
+
+@example
+date +%d/%m -d "Feb 1"
+@result{} 01/02
+date +%-d/%-m -d "Feb 1"
+@result{} 1/2
+date +%_d/%_m -d "Feb 1"
+@result{} 1/ 2
+@end example
+
+
+@node Setting the time
+@subsection Setting the time
+
+@cindex setting the time
+@cindex time setting
+@cindex appropriate privileges
+
+If given an argument that does not start with @samp{+}, @code{date} sets
+the system clock to the time and date specified by that argument (as
+described below). You must have appropriate privileges to set the
+system clock. The @samp{--date} and @samp{--set} options may not be
+used with such an argument. The @samp{--universal} option may be used
+with such an argument to indicate that the specified time and date are
+relative to Coordinated Universal Time rather than to the local time
+zone.
+
+The argument must consist entirely of digits, which have the following
+meaning:
+
+@table @samp
+@item MM
+month
+@item DD
+day within month
+@item hh
+hour
+@item mm
+minute
+@item CC
+first two digits of year (optional)
+@item YY
+last two digits of year (optional)
+@item ss
+second (optional)
+@end table
+
+The @samp{--set} option also sets the system clock; see the next section.
+
+
+@node Options for date
+@subsection Options for @code{date}
+
+@cindex @code{date} options
+@cindex options for @code{date}
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -d @var{datestr}
+@itemx --date=@var{datestr}
+@opindex -d
+@opindex --date
+@cindex parsing date strings
+@cindex date strings, parsing
+@cindex arbitrary date strings, parsing
+@opindex yesterday
+@opindex tomorrow
+@opindex next @var{day}
+@opindex last @var{day}
+Display the time and date specified in @var{datestr} instead of the
+current time and date. @var{datestr} can be in almost any common
+format. It can contain month names, time zones, @samp{am} and @samp{pm},
+@samp{yesterday}, @samp{ago}, @samp{next}, etc. @xref{Date input formats}.
+
+@item -f @var{datefile}
+@itemx --file=@var{datefile}
+@opindex -f
+@opindex --file
+Parse each line in @var{datefile} as with @samp{-d} and display the
+resulting time and date. If @var{datefile} is @samp{-}, use standard
+input. This is useful when you have many dates to process, because the
+system overhead of starting up the @code{date} executable many times can
+be considerable.
+
+@item -I[@var{timespec}]
+@itemx --iso-8601[=@var{timespec}]
+@opindex -I[@var{timespec}]
+@opindex --iso-8601[=@var{timespec}]
+Display the date using the ISO 8601 format, @samp{%Y-%m-%d}.
+
+The optional argument @var{timespec} specifies the number of additional
+terms of the time to include. It can be one of the following:
+@table @samp
+@item auto
+The default behavior: print just the date.
+
+@item hours
+Append the hour of the day to the date.
+
+@item minutes
+Append the hours and minutes.
+
+@item seconds
+Append the hours, minutes, and seconds.
+@end table
+
+If showing any time terms, then include the time zone using the format
+@samp{%z}.
+
+@item -R
+@itemx --rfc-822
+@opindex -R
+@opindex --rfc-822
+Display the time and date using the RFC-822-conforming
+format, @samp{%a, %_d %b %Y %H:%M:%S %z}.
+
+@item -r @var{file}
+@itemx --reference=@var{file}
+@opindex -r
+@opindex --reference
+Display the time and date reference according to the last modification
+time of @var{file}, instead of the current time and date.
+
+@item -s @var{datestr}
+@itemx --set=@var{datestr}
+@opindex -s
+@opindex --set
+Set the time and date to @var{datestr}. See @samp{-d} above.
+
+@item -u
+@itemx --utc
+@itemx --universal
+@opindex -u
+@opindex --utc
+@opindex --universal
+@cindex Coordinated Universal Time
+@cindex UTC
+@cindex Greenwich Mean Time
+@cindex GMT
+Use Coordinated Universal Time (@sc{utc}) by operating as if the
+@env{TZ} environment variable were set to the string @samp{UTC0}.
+Normally, @command{date} operates in the time zone indicated by
+@env{TZ}, or the system default if @env{TZ} is not set. Coordinated
+Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
+historical reasons.
+@end table
+
+
+@node Examples of date
+@subsection Examples of @code{date}
+
+@cindex examples of @code{date}
+
+Here are a few examples. Also see the documentation for the @samp{-d}
+option in the previous section.
+
+@itemize @bullet
+
+@item
+To print the date of the day before yesterday:
+
+@example
+date --date='2 days ago'
+@end example
+
+@item
+To print the date of the day three months and one day hence:
+@example
+date --date='3 months 1 day'
+@end example
+
+@item
+To print the day of year of Christmas in the current year:
+@example
+date --date='25 Dec' +%j
+@end example
+
+@item
+To print the current full month name and the day of the month:
+@example
+date '+%B %d'
+@end example
+
+But this may not be what you want because for the first nine days of
+the month, the @samp{%d} expands to a zero-padded two-digit field,
+for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
+
+@item
+To print a date without the leading zero for one-digit days
+of the month, you can use the (GNU extension) @code{-} modifier to suppress
+the padding altogether.
+@example
+date -d 1may '+%B %-d
+@end example
+
+@item
+To print the current date and time in the format required by many
+non-GNU versions of @code{date} when setting the system clock:
+@example
+date +%m%d%H%M%Y.%S
+@end example
+
+@item
+To set the system clock forward by two minutes:
+@example
+date --set='+2 minutes'
+@end example
+
+@item
+To print the date in the format specified by RFC-822,
+use @samp{date --rfc}. I just did and saw this:
+
+@example
+Mon, 25 Mar 1996 23:34:17 -0600
+@end example
+
+@item
+To convert a date string to the number of seconds since the epoch
+(which is 1970-01-01 00:00:00 UTC), use the @samp{--date} option with
+the @samp{%s} format. That can be useful in sorting and/or graphing
+and/or comparing data by date. The following command outputs the
+number of the seconds since the epoch for the time two minutes after the
+epoch:
+
+@example
+date --date='1970-01-01 00:02:00 +0000' +%s
+120
+@end example
+
+If you do not specify time zone information in the date string,
+@command{date} uses your computer's idea of the time zone when
+interpreting the string. For example, if your computer's time zone is
+that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
+seconds) behind UTC:
+
+@example
+# local time zone used
+date --date='1970-01-01 00:02:00' +%s
+18120
+@end example
+
+@item
+If you're sorting or graphing dated data, your raw date values may be
+represented as seconds since the epoch. But few people can look at
+the date @samp{946684800} and casually note ``Oh, that's the first second
+of the year 2000 in Greenwich, England.''
+
+@example
+date --date='2000-01-01 UTC' +%s
+946684800
+@end example
+
+To convert such an unwieldy number of seconds back to
+a more readable form, use a command like this:
+
+@smallexample
+# local time zone used
+date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
+1999-12-31 19:00:00 -0500
+@end smallexample
+
+@end itemize
+
+
+@node uname invocation
+@section @code{uname}: Print system information
+
+@pindex uname
+@cindex print system information
+@cindex system information, printing
+
+@code{uname} prints information about the machine and operating system
+it is run on. If no options are given, @code{uname} acts as if the
+@code{-s} option were given. Synopsis:
+
+@example
+uname [@var{option}]@dots{}
+@end example
+
+If multiple options or @code{-a} are given, the selected information is
+printed in this order:
+
+@example
+@var{sysname} @var{nodename} @var{release} @var{osversion} @var{machine}
+@end example
+
+The @var{osversion}, at least, may well be multiple words. For example:
+
+@example
+uname -a
+@result{} Linux hayley 1.0.4 #3 Thu May 12 18:06:34 1994 i486
+@end example
+
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Print all of the below information.
+
+@item -m
+@itemx --machine
+@opindex -m
+@opindex --machine
+@cindex machine type
+@cindex hardware type
+Print the machine (hardware) type.
+
+@item -n
+@itemx --nodename
+@opindex -n
+@opindex --nodename
+@cindex hostname
+@cindex node name
+@cindex network node name
+Print the machine's network node hostname.
+
+@item -p
+@itemx --processor
+@opindex -p
+@opindex --processor
+@cindex host processor type
+Print the machine's processor type
+
+@item -r
+@itemx --release
+@opindex -r
+@opindex --release
+@cindex operating system release
+@cindex release of operating system
+Print the operating system release.
+
+@item -s
+@itemx --sysname
+@opindex -s
+@opindex --sysname
+@cindex operating system name
+@cindex name of operating system
+Print the operating system name.
+
+@item -v
+@opindex -v
+@cindex operating system version
+@cindex version of operating system
+Print the operating system version.
+
+@end table
+
+@node hostname invocation
+@section @code{hostname}: Print or set system name
+
+@pindex hostname
+@cindex setting the hostname
+@cindex printing the hostname
+@cindex system name, printing
+@cindex appropriate privileges
+
+With no arguments, @code{hostname} prints the name of the current host
+system. With one argument, it sets the current host name to the
+specified string. You must have appropriate privileges to set the host
+name. Synopsis:
+
+@example
+hostname [@var{name}]
+@end example
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node hostid invocation
+@section @code{hostid}: Print numeric host identifier.
+
+@pindex hostid
+@cindex printing the host identifier
+
+@code{hostid} prints the numeric identifier of the current host
+in hexadecimal. This command accepts no arguments.
+The only options are @samp{--help} and @samp{--version}.
+@xref{Common options}.
+
+For example, here's what it prints on one system I use:
+
+@example
+$ hostid
+1bac013d
+@end example
+
+On that system, the 32-bit quantity happens to be closely
+related to the system's Internet address, but that isn't always
+the case.
+
+
+@node Modified command invocation
+@chapter Modified command invocation
+
+@cindex modified command invocation
+@cindex invocation of commands, modified
+@cindex commands for invoking other commands
+
+This section describes commands that run other commands in some context
+different than the current one: a modified environment, as a different
+user, etc.
+
+@menu
+* chroot invocation:: Modify the root directory.
+* env invocation:: Modify environment variables.
+* nice invocation:: Modify scheduling priority.
+* nohup invocation:: Immunize to hangups.
+* su invocation:: Modify user and group id.
+@end menu
+
+
+@node chroot invocation
+@section @code{chroot}: Run a command with a different root directory
+
+@pindex chroot
+@cindex running a program in a specified root directory
+@cindex root directory, running a program in a specified
+
+@code{chroot} runs a command with a specified root directory.
+On many systems, only the super-user can do this.
+Synopses:
+
+@example
+chroot @var{newroot} [@var{command} [@var{args}]@dots{}]
+chroot @var{option}
+@end example
+
+Ordinarily, filenames are looked up starting at the root of the
+directory structure, i.e., @file{/}. @code{chroot} changes the root to
+the directory @var{newroot} (which must exist) and then runs
+@var{command} with optional @var{args}. If @var{command} is not
+specified, the default is the value of the @env{SHELL} environment
+variable or @code{/bin/sh} if not set, invoked with the @samp{-i} option.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+Here are a few tips to help avoid common problems in using chroot.
+To start with a simple example, make @var{command} refer to a statically
+linked binary. If you were to use a dynamically linked executable, then
+you'd have to arrange to have the shared libraries in the right place under
+your new root directory.
+
+For example, if you create a statically linked `ls' executable,
+and put it in /tmp/empty, you can run this command as root:
+
+@example
+$ chroot /tmp/empty /ls -Rl /
+@end example
+
+Then you'll see output like this:
+
+@example
+/:
+total 1023
+-rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
+@end example
+
+If you want to use a dynamically linked executable, say @code{bash},
+then first run @samp{ldd bash} to see what shared objects it needs.
+Then, in addition to copying the actual binary, also copy the listed
+files to the required positions under your intended new root directory.
+Finally, if the executable requires any other files (e.g., data, state,
+device files), copy them into place, too.
+
+
+@node env invocation
+@section @code{env}: Run a command in a modified environment
+
+@pindex env
+@cindex environment, running a program in a modified
+@cindex modified environment, running a program in a
+@cindex running a program in a modified environment
+
+@code{env} runs a command with a modified environment. Synopses:
+
+@example
+env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
+[@var{command} [@var{args}]@dots{}]
+env
+@end example
+
+Arguments of the form @samp{@var{variable}=@var{value}} set
+the environment variable @var{variable} to value @var{value}.
+@var{value} may be empty (@samp{@var{variable}=}). Setting a variable
+to an empty value is different from unsetting it.
+
+@vindex PATH
+The first remaining argument specifies the program name to invoke; it is
+searched for according to the @env{PATH} environment variable. Any
+remaining arguments are passed as arguments to that program.
+
+@cindex environment, printing
+
+If no command name is specified following the environment
+specifications, the resulting environment is printed. This is like
+specifying a command name of @code{printenv}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -u @var{name}
+@itemx --unset=@var{name}
+@opindex -u
+@opindex -unset
+Remove variable @var{name} from the environment, if it was in the
+environment.
+
+@item -
+@itemx -i
+@itemx --ignore-environment
+@opindex -
+@opindex -i
+@opindex --ignore-environment
+Start with an empty environment, ignoring the inherited environment.
+
+@end table
+
+
+@node nice invocation
+@section @code{nice}: Run a command with modified scheduling priority
+
+@pindex nice
+@cindex modifying scheduling priority
+@cindex scheduling priority, modifying
+@cindex priority, modifying
+@cindex appropriate privileges
+
+@code{nice} prints or modifies the scheduling priority of a job.
+Synopsis:
+
+@example
+nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
+@end example
+
+If no arguments are given, @code{nice} prints the current scheduling
+priority, which it inherited. Otherwise, @code{nice} runs the given
+@var{command} with its scheduling priority adjusted. If no
+@var{adjustment} is given, the priority of the command is incremented by
+10. You must have appropriate privileges to specify a negative
+adjustment. The priority can be adjusted by @code{nice} over the range
+of -20 (the highest priority) to 19 (the lowest).
+
+@cindex conflicts with shell built-ins
+@cindex built-in shell commands, conflicts with
+Because most shells have a built-in command by the same name, using the
+unadorned command name in a script or interactively may get you
+different functionality than that described here.
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+@item -n @var{adjustment}
+@itemx -@var{adjustment}
+@itemx --adjustment=@var{adjustment}
+@opindex -n
+@opindex --adjustment
+@opindex -@var{adjustment}
+Add @var{adjustment} instead of 10 to the command's priority.
+@end table
+
+
+@node nohup invocation
+@section @code{nohup}: Run a command immune to hangups
+
+@pindex nohup
+@cindex hangups, immunity to
+@cindex immunity to hangups
+@cindex logging out and continuing to run
+
+@flindex nohup.out
+@code{nohup} runs the given @var{command} with hangup signals ignored,
+so that the command can continue running in the background after you log
+out. Synopsis:
+
+@example
+nohup @var{command} [@var{arg}]@dots{}
+@end example
+
+@flindex nohup.out
+@code{nohup} increases the scheduling priority of @var{command} by 5, so
+it has a slightly smaller chance to run. If standard output is a terminal,
+it and standard error are redirected so that they are appended to the
+file @file{nohup.out}; if that cannot be written to, they are appended
+to the file @file{$HOME/nohup.out}. If that cannot be written to, the
+command is not run.
+
+If @code{nohup} creates either @file{nohup.out} or
+@file{$HOME/nohup.out}, it creates it with no ``group'' or ``other''
+access permissions. It does not change the permissions if the output
+file already existed.
+
+@code{nohup} does not automatically put the command it runs in the
+background; you must do that explicitly, by ending the command line
+with an @samp{&}.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node su invocation
+@section @code{su}: Run a command with substitute user and group id
+
+@pindex su
+@cindex substitute user and group ids
+@cindex user id, switching
+@cindex super-user, becoming
+@cindex root, becoming
+
+@code{su} allows one user to temporarily become another user. It runs a
+command (often an interactive shell) with the real and effective user
+id, group id, and supplemental groups of a given @var{user}. Synopsis:
+
+@example
+su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
+@end example
+
+@cindex passwd entry, and @code{su} shell
+@flindex /bin/sh
+@flindex /etc/passwd
+If no @var{user} is given, the default is @code{root}, the super-user.
+The shell to use is taken from @var{user}'s @code{passwd} entry, or
+@file{/bin/sh} if none is specified there. If @var{user} has a
+password, @code{su} prompts for the password unless run by a user with
+effective user id of zero (the super-user).
+
+@vindex HOME
+@vindex SHELL
+@vindex USER
+@vindex LOGNAME
+@cindex login shell
+By default, @code{su} does not change the current directory.
+It sets the environment variables @env{HOME} and @env{SHELL}
+from the password entry for @var{user}, and if @var{user} is not
+the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
+By default, the shell is not a login shell.
+
+Any additional @var{arg}s are passed as additional arguments to the
+shell.
+
+@cindex @samp{-su}
+GNU @code{su} does not treat @file{/bin/sh} or any other shells specially
+(e.g., by setting @code{argv[0]} to @samp{-su}, passing @code{-c} only
+to certain shells, etc.).
+
+@findex syslog
+@code{su} can optionally be compiled to use @code{syslog} to report
+failed, and optionally successful, @code{su} attempts. (If the system
+supports @code{syslog}.) However, GNU @code{su} does not check if the
+user is a member of the @code{wheel} group; see below.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -c @var{command}
+@itemx --command=@var{command}
+@opindex -c
+@opindex --command
+Pass @var{command}, a single command line to run, to the shell with
+a @code{-c} option instead of starting an interactive shell.
+
+@item -f
+@itemx --fast
+@opindex -f
+@opindex --fast
+@flindex .cshrc
+@cindex file name pattern expansion, disabled
+@cindex globbing, disabled
+Pass the @code{-f} option to the shell. This probably only makes sense
+if the shell run is @code{csh} or @code{tcsh}, for which the @code{-f}
+option prevents reading the startup file (@file{.cshrc}). With
+Bourne-like shells, the @code{-f} option disables file name pattern
+expansion (globbing), which is not likely to be useful.
+
+@item -
+@itemx -l
+@itemx --login
+@opindex -
+@opindex -l
+@opindex --login
+@c other variables already indexed above
+@vindex TERM
+@vindex PATH
+@cindex login shell, creating
+Make the shell a login shell. This means the following. Unset all
+environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
+(which are set as described above), and @env{USER} and @env{LOGNAME}
+(which are set, even for the super-user, as described above), and set
+@env{PATH} to a compiled-in default value. Change to @var{user}'s home
+directory. Prepend @samp{-} to the shell's name, intended to make it
+read its login startup file(s).
+
+@item -m
+@itemx -p
+@itemx --preserve-environment
+@opindex -m
+@opindex -p
+@opindex --preserve-environment
+@cindex environment, preserving
+@flindex /etc/shells
+@cindex restricted shell
+Do not change the environment variables @env{HOME}, @env{USER},
+@env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
+variable @env{SHELL} instead of the shell from @var{user}'s passwd
+entry, unless the user running @code{su} is not the superuser and
+@var{user}'s shell is restricted. A @dfn{restricted shell} is one that
+is not listed in the file @file{/etc/shells}, or in a compiled-in list
+if that file does not exist. Parts of what this option does can be
+overridden by @code{--login} and @code{--shell}.
+
+@item -s @var{shell}
+@itemx --shell=@var{shell}
+@opindex -s
+@opindex --shell
+Run @var{shell} instead of the shell from @var{user}'s passwd entry,
+unless the user running @code{su} is not the superuser and @var{user}'s
+shell is restricted (see @samp{-m} just above).
+
+@end table
+
+@cindex wheel group, not supported
+@cindex group wheel, not supported
+@cindex fascism
+@heading Why GNU @code{su} does not support the @samp{wheel} group
+
+(This section is by Richard Stallman.)
+
+@cindex Twenex
+@cindex MIT AI lab
+Sometimes a few of the users try to hold total power over all the
+rest. For example, in 1984, a few users at the MIT AI lab decided to
+seize power by changing the operator password on the Twenex system and
+keeping it secret from everyone else. (I was able to thwart this coup
+and give power back to the users by patching the kernel, but I
+wouldn't know how to do that in Unix.)
+
+However, occasionally the rulers do tell someone. Under the usual
+@code{su} mechanism, once someone learns the root password who
+sympathizes with the ordinary users, he or she can tell the rest. The
+``wheel group'' feature would make this impossible, and thus cement the
+power of the rulers.
+
+I'm on the side of the masses, not that of the rulers. If you are
+used to supporting the bosses and sysadmins in whatever they do, you
+might find this idea strange at first.
+
+
+@node Delaying
+@chapter Delaying
+
+@cindex delaying commands
+@cindex commands for delaying
+
+@c Perhaps @code{wait} or other commands should be described here also?
+
+@menu
+* sleep invocation:: Delay for a specified time.
+@end menu
+
+
+@node sleep invocation
+@section @code{sleep}: Delay for a specified time
+
+@pindex sleep
+@cindex delay for a specified time
+
+@code{sleep} pauses for an amount of time specified by the sum of
+the values of the command line arguments.
+Synopsis:
+
+@example
+sleep @var{number}[smhd]@dots{}
+@end example
+
+@cindex time units
+Each argument is a number followed by an optional unit; the default
+is seconds. The units are:
+
+@table @samp
+@item s
+seconds
+@item m
+minutes
+@item h
+hours
+@item d
+days
+@end table
+
+Historical implementations of @code{sleep} have required that
+@var{number} be an integer. However, GNU @code{sleep} accepts
+arbitrary floating point numbers.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+
+@node Numeric operations
+@chapter Numeric operations
+
+@cindex numeric operations
+These programs do numerically-related operations.
+
+@menu
+* factor invocation:: Show factors of numbers.
+* seq invocation:: Print sequences of numbers.
+@end menu
+
+
+@node factor invocation
+@section @code{factor}: Print prime factors
+
+@pindex factor
+@cindex prime factors
+
+@code{factor} prints prime factors. Synopses:
+
+@example
+factor [@var{number}]@dots{}
+factor @var{option}
+@end example
+
+If no @var{number} is specified on the command line, @code{factor} reads
+numbers from standard input, delimited by newlines, tabs, or spaces.
+
+The only options are @samp{--help} and @samp{--version}. @xref{Common
+options}.
+
+The algorithm it uses is not very sophisticated, so for some inputs
+@code{factor} runs for a long time. The hardest numbers to factor are
+the products of large primes. Factoring the product of the two largest 32-bit
+prime numbers takes over 10 minutes of CPU time on a 400MHz Pentium II.
+
+@example
+$ p=`echo '4294967279 * 4294967291'|bc`
+$ factor $p
+18446743979220271189: 4294967279 4294967291
+@end example
+
+In contrast, @code{factor} factors the largest 64-bit number in just
+over a tenth of a second:
+
+@example
+$ factor `echo '2^64-1'|bc`
+18446744073709551615: 3 5 17 257 641 65537 6700417
+@end example
+
+@node seq invocation
+@section @code{seq}: Print numeric sequences
+
+@pindex seq
+@cindex numeric sequences
+@cindex sequence of numbers
+
+@code{seq} prints a sequence of numbers to standard output. Synopses:
+
+@example
+seq [@var{option}]@dots{} [@var{first} [@var{increment}]] @var{last}@dots{}
+@end example
+
+@code{seq} prints the numbers from @var{first} to @var{last} by
+@var{increment}. By default, @var{first} and @var{increment} are both 1,
+and each number is printed on its own line. All numbers can be reals,
+not just integers.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -f @var{format}
+@itemx --format=@var{format}
+@opindex -f @var{format}
+@opindex --format=@var{format}
+@cindex formatting of numbers in @code{seq}
+Print all numbers using @var{format}; default @samp{%g}.
+@var{format} must contain exactly one of the floating point
+output formats @samp{%e}, @samp{%f}, or @samp{%g}.
+
+@item -s @var{string}
+@itemx --separator=@var{string}
+@cindex separator for numbers in @code{seq}
+Separate numbers with @var{string}; default is a newline.
+The output always terminates with a newline.
+
+@item -w
+@itemx --equal-width
+Print all numbers with the same width, by padding with leading zeroes.
+(To have other kinds of padding, use @samp{--format}).
+
+@end table
+
+If you want to use @code{seq} to print sequences of large integer values,
+don't use the default @samp{%g} format since it can result in
+loss of precision:
+
+@example
+$ seq 1000000 1000001
+1e+06
+1e+06
+@end example
+
+Instead, you can use the format, @samp{%1.f},
+to print large decimal numbers with no exponent and no decimal point.
+
+@example
+$ seq --format=%1.f 1000000 1000001
+1000000
+1000001
+@end example
+
+If you want hexadecimal output, you can use @code{printf}
+to perform the conversion:
+
+@example
+$ printf %x'\n' `seq -f %1.f 1048575 1024 1050623`
+fffff
+1003ff
+1007ff
+@end example
+
+For very long lists of numbers, use xargs to avoid
+system limitations on the length of an argument list:
+
+@example
+$ seq -f %1.f 1000000 | xargs printf %x'\n' |tail -3
+f423e
+f423f
+f4240
+@end example
+
+To generate octal output, use the printf @code{%o} format instead
+of @code{%x}. Note however that using printf works only for numbers
+smaller than @code{2^32}:
+
+@example
+$ printf "%x\n" `seq -f %1.f 4294967295 4294967296`
+ffffffff
+bash: printf: 4294967296: Numerical result out of range
+@end example
+
+On most systems, seq can produce whole-number output for values up to
+@code{2^53}, so here's a more general approach to base conversion that
+also happens to be more robust for such large numbers. It works by
+using @code{bc} and setting its output radix variable, @var{obase},
+to @samp{16} in this case to produce hexadecimal output.
+
+@example
+$ (echo obase=16; seq -f %1.f 4294967295 4294967296)|bc
+FFFFFFFF
+100000000
+@end example
+
+Be careful when using @code{seq} with a fractional @var{increment},
+otherwise you may see surprising results. Most people would expect to
+see @code{0.3} printed as the last number in this example:
+
+@example
+$ seq -s' ' 0 .1 .3
+0 0.1 0.2
+@end example
+
+But that doesn't happen on most systems because @code{seq} is
+implemented using binary floating point arithmetic (via the C
+@code{double} type) -- which means some decimal numbers like @code{.1}
+cannot be represented exactly. That in turn means some nonintuitive
+conditions like @code{.1 * 3 > .3} will end up being true.
+
+To work around that in the above example, use a slightly larger number as
+the @var{last} value:
+
+@example
+$ seq -s' ' 0 .1 .31
+0 0.1 0.2 0.3
+@end example
+
+In general, when using an @var{increment} with a fractional part, where
+(@var{last} - @var{first}) / @var{increment} is (mathematically) a whole
+number, specify a slightly larger (or smaller, if @var{increment} is negative)
+value for @var{last} to ensure that @var{last} is the final value printed
+by seq.
+
+@node File permissions
+@chapter File permissions
+@include perm.texi
+
+@include getdate.texi
+
+@c What's GNU?
+@c Arnold Robbins
+@node Opening the software toolbox
+@chapter Opening the Software Toolbox
+
+This chapter originally appeared in @cite{Linux Journal}, volume 1,
+number 2, in the @cite{What's GNU?} column. It was written by Arnold
+Robbins.
+
+@menu
+* Toolbox introduction:: Toolbox introduction
+* I/O redirection:: I/O redirection
+* The who command:: The @command{who} command
+* The cut command:: The @command{cut} command
+* The sort command:: The @command{sort} command
+* The uniq command:: The @command{uniq} command
+* Putting the tools together:: Putting the tools together
+@end menu
+
+
+@node Toolbox introduction
+@unnumberedsec Toolbox Introduction
+
+This month's column is only peripherally related to the GNU Project, in
+that it describes a number of the GNU tools on your GNU/Linux system and how they
+might be used. What it's really about is the ``Software Tools'' philosophy
+of program development and usage.
+
+The software tools philosophy was an important and integral concept
+in the initial design and development of Unix (of which Linux and GNU are
+essentially clones). Unfortunately, in the modern day press of
+Internetworking and flashy GUIs, it seems to have fallen by the
+wayside. This is a shame, since it provides a powerful mental model
+for solving many kinds of problems.
+
+Many people carry a Swiss Army knife around in their pants pockets (or
+purse). A Swiss Army knife is a handy tool to have: it has several knife
+blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
+a number of other things on it. For the everyday, small miscellaneous jobs
+where you need a simple, general purpose tool, it's just the thing.
+
+On the other hand, an experienced carpenter doesn't build a house using
+a Swiss Army knife. Instead, he has a toolbox chock full of specialized
+tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
+exactly when and where to use each tool; you won't catch him hammering nails
+with the handle of his screwdriver.
+
+The Unix developers at Bell Labs were all professional programmers and trained
+computer scientists. They had found that while a one-size-fits-all program
+might appeal to a user because there's only one program to use, in practice
+such programs are
+
+@enumerate a
+@item
+difficult to write,
+
+@item
+difficult to maintain and
+debug, and
+
+@item
+difficult to extend to meet new situations.
+@end enumerate
+
+Instead, they felt that programs should be specialized tools. In short, each
+program ``should do one thing well.'' No more and no less. Such programs are
+simpler to design, write, and get right---they only do one thing.
+
+Furthermore, they found that with the right machinery for hooking programs
+together, that the whole was greater than the sum of the parts. By combining
+several special purpose programs, you could accomplish a specific task
+that none of the programs was designed for, and accomplish it much more
+quickly and easily than if you had to write a special purpose program.
+We will see some (classic) examples of this further on in the column.
+(An important additional point was that, if necessary, take a detour
+and build any software tools you may need first, if you don't already
+have something appropriate in the toolbox.)
+
+@node I/O redirection
+@unnumberedsec I/O Redirection
+
+Hopefully, you are familiar with the basics of I/O redirection in the
+shell, in particular the concepts of ``standard input,'' ``standard output,''
+and ``standard error''. Briefly, ``standard input'' is a data source, where
+data comes from. A program should not need to either know or care if the
+data source is a disk file, a keyboard, a magnetic tape, or even a punched
+card reader. Similarly, ``standard output'' is a data sink, where data goes
+to. The program should neither know nor care where this might be.
+Programs that only read their standard input, do something to the data,
+and then send it on, are called @dfn{filters}, by analogy to filters in a
+water pipeline.
+
+With the Unix shell, it's very easy to set up data pipelines:
+
+@smallexample
+program_to_create_data | filter1 | .... | filterN > final.pretty.data
+@end smallexample
+
+We start out by creating the raw data; each filter applies some successive
+transformation to the data, until by the time it comes out of the pipeline,
+it is in the desired form.
+
+This is fine and good for standard input and standard output. Where does the
+standard error come in to play? Well, think about @command{filter1} in
+the pipeline above. What happens if it encounters an error in the data it
+sees? If it writes an error message to standard output, it will just
+disappear down the pipeline into @command{filter2}'s input, and the
+user will probably never see it. So programs need a place where they can send
+error messages so that the user will notice them. This is standard error,
+and it is usually connected to your console or window, even if you have
+redirected standard output of your program away from your screen.
+
+For filter programs to work together, the format of the data has to be
+agreed upon. The most straightforward and easiest format to use is simply
+lines of text. Unix data files are generally just streams of bytes, with
+lines delimited by the @sc{ascii} @sc{lf} (Line Feed) character,
+conventionally called a ``newline'' in the Unix literature. (This is
+@code{'\n'} if you're a C programmer.) This is the format used by all
+the traditional filtering programs. (Many earlier operating systems
+had elaborate facilities and special purpose programs for managing
+binary data. Unix has always shied away from such things, under the
+philosophy that it's easiest to simply be able to view and edit your
+data with a text editor.)
+
+OK, enough introduction. Let's take a look at some of the tools, and then
+we'll see how to hook them together in interesting ways. In the following
+discussion, we will only present those command line options that interest
+us. As you should always do, double check your system documentation
+for the full story.
+
+@node The who command
+@unnumberedsec The @command{who} Command
+
+The first program is the @command{who} command. By itself, it generates a
+list of the users who are currently logged in. Although I'm writing
+this on a single-user system, we'll pretend that several people are
+logged in:
+
+@example
+$ who
+@print{} arnold console Jan 22 19:57
+@print{} miriam ttyp0 Jan 23 14:19(:0.0)
+@print{} bill ttyp1 Jan 21 09:32(:0.0)
+@print{} arnold ttyp2 Jan 23 20:48(:0.0)
+@end example
+
+Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
+There are three people logged in, and I am logged in twice. On traditional
+Unix systems, user names are never more than eight characters long. This
+little bit of trivia will be useful later. The output of @command{who} is nice,
+but the data is not all that exciting.
+
+@node The cut command
+@unnumberedsec The @command{cut} Command
+
+The next program we'll look at is the @command{cut} command. This program
+cuts out columns or fields of input data. For example, we can tell it
+to print just the login name and full name from the @file{/etc/passwd}
+file. The @file{/etc/passwd} file has seven fields, separated by
+colons:
+
+@example
+arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
+@end example
+
+To get the first and fifth fields, we would use @command{cut} like this:
+
+@example
+$ cut -d: -f1,5 /etc/passwd
+@print{} root:Operator
+@dots{}
+@print{} arnold:Arnold D. Robbins
+@print{} miriam:Miriam A. Robbins
+@dots{}
+@end example
+
+With the @option{-c} option, @command{cut} will cut out specific characters
+(i.e., columns) in the input lines. This command looks like it might be
+useful for data filtering.
+
+
+@node The sort command
+@unnumberedsec The @command{sort} Command
+
+Next we'll look at the @command{sort} command. This is one of the most
+powerful commands on a Unix-style system; one that you will often find
+yourself using when setting up fancy data plumbing.
+
+The @command{sort}
+command reads and sorts each file named on the command line. It then
+merges the sorted data and writes it to standard output. It will read
+standard input if no files are given on the command line (thus
+making it into a filter). The sort is based on the character collating
+sequence or based on user-supplied ordering criteria.
+
+
+@node The uniq command
+@unnumberedsec The @command{uniq} Command
+
+Finally (at least for now), we'll look at the @command{uniq} program. When
+sorting data, you will often end up with duplicate lines, lines that
+are identical. Usually, all you need is one instance of each line.
+This is where @command{uniq} comes in. The @command{uniq} program reads its
+standard input, which it expects to be sorted. It only prints out one
+copy of each duplicated line. It does have several options. Later on,
+we'll use the @option{-c} option, which prints each unique line, preceded
+by a count of the number of times that line occurred in the input.
+
+
+@node Putting the tools together
+@unnumberedsec Putting the Tools Together
+
+Now, let's suppose this is a large ISP server system with dozens of users
+logged in. The management wants the system administrator to write a program that will
+generate a sorted list of logged in users. Furthermore, even if a user
+is logged in multiple times, his or her name should only show up in the
+output once.
+
+The administrator could sit down with the system documentation and write a C
+program that did this. It would take perhaps a couple of hundred lines
+of code and about two hours to write it, test it, and debug it.
+However, knowing the software toolbox, the administrator can instead start out
+by generating just a list of logged on users:
+
+@example
+$ who | cut -c1-8
+@print{} arnold
+@print{} miriam
+@print{} bill
+@print{} arnold
+@end example
+
+Next, sort the list:
+
+@example
+$ who | cut -c1-8 | sort
+@print{} arnold
+@print{} arnold
+@print{} bill
+@print{} miriam
+@end example
+
+Finally, run the sorted list through @command{uniq}, to weed out duplicates:
+
+@example
+$ who | cut -c1-8 | sort | uniq
+@print{} arnold
+@print{} bill
+@print{} miriam
+@end example
+
+The @command{sort} command actually has a @option{-u} option that does what
+@command{uniq} does. However, @command{uniq} has other uses for which one
+cannot substitute @samp{sort -u}.
+
+The administrator puts this pipeline into a shell script, and makes it available for
+all the users on the system (@samp{#} is the system administrator,
+or @code{root}, prompt):
+
+@example
+# cat > /usr/local/bin/listusers
+who | cut -c1-8 | sort | uniq
+^D
+# chmod +x /usr/local/bin/listusers
+@end example
+
+There are four major points to note here. First, with just four
+programs, on one command line, the administrator was able to save about two
+hours worth of work. Furthermore, the shell pipeline is just about as
+efficient as the C program would be, and it is much more efficient in
+terms of programmer time. People time is much more expensive than
+computer time, and in our modern ``there's never enough time to do
+everything'' society, saving two hours of programmer time is no mean
+feat.
+
+Second, it is also important to emphasize that with the
+@emph{combination} of the tools, it is possible to do a special
+purpose job never imagined by the authors of the individual programs.
+
+Third, it is also valuable to build up your pipeline in stages, as we did here.
+This allows you to view the data at each stage in the pipeline, which helps
+you acquire the confidence that you are indeed using these tools correctly.
+
+Finally, by bundling the pipeline in a shell script, other users can use
+your command, without having to remember the fancy plumbing you set up for
+them. In terms of how you run them, shell scripts and compiled programs are
+indistinguishable.
+
+After the previous warm-up exercise, we'll look at two additional, more
+complicated pipelines. For them, we need to introduce two more tools.
+
+The first is the @command{tr} command, which stands for ``transliterate.''
+The @command{tr} command works on a character-by-character basis, changing
+characters. Normally it is used for things like mapping upper case to
+lower case:
+
+@example
+$ echo ThIs ExAmPlE HaS MIXED case! | tr '[A-Z]' '[a-z]'
+@print{} this example has mixed case!
+@end example
+
+There are several options of interest:
+
+@table @code
+@item -c
+work on the complement of the listed characters, i.e.,
+operations apply to characters not in the given set
+
+@item -d
+delete characters in the first set from the output
+
+@item -s
+squeeze repeated characters in the output into just one character.
+@end table
+
+We will be using all three options in a moment.
+
+The other command we'll look at is @command{comm}. The @command{comm}
+command takes two sorted input files as input data, and prints out the
+files' lines in three columns. The output columns are the data lines
+unique to the first file, the data lines unique to the second file, and
+the data lines that are common to both. The @option{-1}, @option{-2}, and
+@option{-3} command line options @emph{omit} the respective columns. (This is
+non-intuitive and takes a little getting used to.) For example:
+
+@example
+$ cat f1
+@print{} 11111
+@print{} 22222
+@print{} 33333
+@print{} 44444
+$ cat f2
+@print{} 00000
+@print{} 22222
+@print{} 33333
+@print{} 55555
+$ comm f1 f2
+@print{} 00000
+@print{} 11111
+@print{} 22222
+@print{} 33333
+@print{} 44444
+@print{} 55555
+@end example
+
+The single dash as a filename tells @command{comm} to read standard input
+instead of a regular file.
+
+Now we're ready to build a fancy pipeline. The first application is a word
+frequency counter. This helps an author determine if he or she is over-using
+certain words.
+
+The first step is to change the case of all the letters in our input file
+to one case. ``The'' and ``the'' are the same word when doing counting.
+
+@example
+$ tr '[A-Z]' '[a-z]' < whats.gnu | ...
+@end example
+
+The next step is to get rid of punctuation. Quoted words and unquoted words
+should be treated identically; it's easiest to just get the punctuation out of
+the way.
+
+@smallexample
+$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' | ...
+@end smallexample
+
+The second @command{tr} command operates on the complement of the listed
+characters, which are all the letters, the digits, the underscore, and
+the blank. The @samp{\012} represents the newline character; it has to
+be left alone. (The @sc{ascii} tab character should also be included for
+good measure in a production script.)
+
+At this point, we have data consisting of words separated by blank space.
+The words only contain alphanumeric characters (and the underscore). The
+next step is break the data apart so that we have one word per line. This
+makes the counting operation much easier, as we will see shortly.
+
+@smallexample
+$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
+> tr -s '[ ]' '\012' | ...
+@end smallexample
+
+This command turns blanks into newlines. The @option{-s} option squeezes
+multiple newline characters in the output into just one. This helps us
+avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
+This is what the shell prints when it notices you haven't finished
+typing in all of a command.)
+
+We now have data consisting of one word per line, no punctuation, all one
+case. We're ready to count each word:
+
+@smallexample
+$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
+> tr -s '[ ]' '\012' | sort | uniq -c | ...
+@end smallexample
+
+At this point, the data might look something like this:
+
+@example
+ 60 a
+ 2 able
+ 6 about
+ 1 above
+ 2 accomplish
+ 1 acquire
+ 1 actually
+ 2 additional
+@end example
+
+The output is sorted by word, not by count! What we want is the most
+frequently used words first. Fortunately, this is easy to accomplish,
+with the help of two more @command{sort} options:
+
+@table @code
+@item -n
+do a numeric sort, not a textual one
+
+@item -r
+reverse the order of the sort
+@end table
+
+The final pipeline looks like this:
+
+@smallexample
+$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
+> tr -s '[ ]' '\012' | sort | uniq -c | sort -nr
+@print{} 156 the
+@print{} 60 a
+@print{} 58 to
+@print{} 51 of
+@print{} 51 and
+@dots{}
+@end smallexample
+
+Whew! That's a lot to digest. Yet, the same principles apply. With six
+commands, on two lines (really one long one split for convenience), we've
+created a program that does something interesting and useful, in much
+less time than we could have written a C program to do the same thing.
+
+A minor modification to the above pipeline can give us a simple spelling
+checker! To determine if you've spelled a word correctly, all you have to
+do is look it up in a dictionary. If it is not there, then chances are
+that your spelling is incorrect. So, we need a dictionary.
+The conventional location for a dictionary is @file{/usr/dict/words}.
+On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
+revision of this article.}
+this is a is a sorted, 45,402 word dictionary.
+
+Now, how to compare our file with the dictionary? As before, we generate
+a sorted list of words, one per line:
+
+@smallexample
+$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
+> tr -s '[ ]' '\012' | sort -u | ...
+@end smallexample
+
+Now, all we need is a list of words that are @emph{not} in the
+dictionary. Here is where the @command{comm} command comes in.
+
+@smallexample
+$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
+> tr -s '[ ]' '\012' | sort -u |
+> comm -23 - /usr/dict/words
+@end smallexample
+
+The @option{-2} and @option{-3} options eliminate lines that are only in the
+dictionary (the second file), and lines that are in both files. Lines
+only in the first file (standard input, our stream of words), are
+words that are not in the dictionary. These are likely candidates for
+spelling errors. This pipeline was the first cut at a production
+spelling checker on Unix.
+
+There are some other tools that deserve brief mention.
+
+@table @command
+@item grep
+search files for text that matches a regular expression
+
+@item egrep
+like @command{grep}, but with more powerful regular expressions
+
+@item wc
+count lines, words, characters
+
+@item tee
+a T-fitting for data pipes, copies data to files and to standard output
+
+@item sed
+the stream editor, an advanced tool
+
+@item awk
+a data manipulation language, another advanced tool
+@end table
+
+The software tools philosophy also espoused the following bit of
+advice: ``Let someone else do the hard part.'' This means, take
+something that gives you most of what you need, and then massage it the
+rest of the way until it's in the form that you want.
+
+To summarize:
+
+@enumerate 1
+@item
+Each program should do one thing well. No more, no less.
+
+@item
+Combining programs with appropriate plumbing leads to results where
+the whole is greater than the sum of the parts. It also leads to novel
+uses of programs that the authors might never have imagined.
+
+@item
+Programs should never print extraneous header or trailer data, since these
+could get sent on down a pipeline. (A point we didn't mention earlier.)
+
+@item
+Let someone else do the hard part.
+
+@item
+Know your toolbox! Use each program appropriately. If you don't have an
+appropriate tool, build one.
+@end enumerate
+
+As of this writing, all the programs we've discussed are available via
+anonymous @command{ftp} from: @*
+@uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
+be more recent versions available now.)
+
+None of what I have presented in this column is new. The Software Tools
+philosophy was first introduced in the book @cite{Software Tools}, by
+Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
+This book showed how to write and use software tools. It was written in
+1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
+FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
+was. The last chapter presented a @command{ratfor} to FORTRAN
+processor, written in @command{ratfor}. @command{ratfor} looks an awful
+lot like C; if you know C, you won't have any problem following the
+code.
+
+In 1981, the book was updated and made available as @cite{Software Tools
+in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). The first book is
+still in print; the second, alas, is not. Both books are well worth
+reading if you're a programmer. They certainly made a major change in
+how I view programming.
+
+Initially, the programs in both books were available (on 9-track tape)
+from Addison-Wesley. Unfortunately, this is no longer the case,
+although the @command{ratfor} versions are available from
+@uref{http://cm.bell-labs.come/who/bwk, Brian Kernighan's home page},
+and you might be able to find copies of the Pascal versions floating
+around the Internet. For a number of years, there was an active
+Software Tools Users Group, whose members had ported the original
+@command{ratfor} programs to essentially every computer system with a
+FORTRAN compiler. The popularity of the group waned in the middle 1980s
+as Unix began to spread beyond universities.
+
+With the current proliferation of GNU code and other clones of Unix programs,
+these programs now receive little attention; modern C versions are
+much more efficient and do more than these programs do. Nevertheless, as
+exposition of good programming style, and evangelism for a still-valuable
+philosophy, these books are unparalleled, and I recommend them highly.
+
+Acknowledgment: I would like to express my gratitude to Brian Kernighan
+of Bell Labs, the original Software Toolsmith, for reviewing this column.
+
+@include doclicense.texi
+
+@node Index
+@unnumbered Index
+
+@printindex cp
+
+@shortcontents
+@contents
+@bye
+
+@c Local variables:
+@c texinfo-column-for-description: 32
+@c End:
projects / platform / upstream / coreutils.git / commitdiff