1 This is the Bash FAQ, version 4.01, for Bash version 4.0.
3 This document contains a set of frequently-asked questions concerning
4 Bash, the GNU Bourne-Again Shell. Bash is a freely-available command
5 interpreter with advanced features for both interactive use and shell
8 Another good source of basic information about shells is the collection
9 of FAQ articles periodically posted to comp.unix.shell.
11 Questions and comments concerning this document should be sent to
14 This document is available for anonymous FTP with the URL
16 ftp://ftp.cwru.edu/pub/bash/FAQ
18 The Bash home page is http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html
26 A2) What's the latest version?
27 A3) Where can I get it?
28 A4) On what machines will bash run?
29 A5) Will bash run on operating systems other than Unix?
30 A6) How can I build bash with gcc?
31 A7) How can I make bash my login shell?
32 A8) I just changed my login shell to bash, and now I can't FTP into my
34 A9) What's the `POSIX Shell and Utilities standard'?
35 A10) What is the bash `posix mode'?
37 Section B: The latest version
39 B1) What's new in version 4.0?
40 B2) Are there any user-visible incompatibilities between bash-4.0,
41 bash-3.2, and bash-2.05b?
43 Section C: Differences from other Unix shells
45 C1) How does bash differ from sh, the Bourne shell?
46 C2) How does bash differ from the Korn shell, version ksh88?
47 C3) Which new features in ksh-93 are not in bash, and which are?
49 Section D: Why does bash do some things differently than other Unix shells?
51 D1) Why does bash run a different version of `command' than
52 `which command' says it will?
53 D2) Why doesn't bash treat brace expansions exactly like csh?
54 D3) Why doesn't bash have csh variable modifiers?
55 D4) How can I make my csh aliases work when I convert to bash?
56 D5) How can I pipe standard output and standard error from one command to
57 another, like csh does with `|&'?
58 D6) Now that I've converted from ksh to bash, are there equivalents to
59 ksh features like autoloaded functions and the `whence' command?
61 Section E: Why does bash do certain things the way it does?
63 E1) Why is the bash builtin `test' slightly different from /bin/test?
64 E2) Why does bash sometimes say `Broken pipe'?
65 E3) When I have terminal escape sequences in my prompt, why does bash
66 wrap lines at the wrong column?
67 E4) If I pipe the output of a command into `read variable', why doesn't
68 the output show up in $variable when the read command finishes?
69 E5) I have a bunch of shell scripts that use backslash-escaped characters
70 in arguments to `echo'. Bash doesn't interpret these characters. Why
71 not, and how can I make it understand them?
72 E6) Why doesn't a while or for loop get suspended when I type ^Z?
73 E7) What about empty for loops in Makefiles?
74 E8) Why does the arithmetic evaluation code complain about `08'?
75 E9) Why does the pattern matching expression [A-Z]* match files beginning
76 with every letter except `z'?
77 E10) Why does `cd //' leave $PWD as `//'?
78 E11) If I resize my xterm while another program is running, why doesn't bash
80 E12) Why don't negative offsets in substring expansion work like I expect?
81 E13) Why does filename completion misbehave if a colon appears in the filename?
82 E14) Why does quoting the pattern argument to the regular expression matching
83 conditional operator (=~) cause matching to stop working?
85 Section F: Things to watch out for on certain Unix versions
87 F1) Why can't I use command line editing in my `cmdtool'?
88 F2) I built bash on Solaris 2. Why do globbing expansions and filename
89 completion chop off the first few characters of each filename?
90 F3) Why does bash dump core after I interrupt username completion or
91 `~user' tilde expansion on a machine running NIS?
92 F4) I'm running SVR4.2. Why is the line erased every time I type `@'?
93 F5) Why does bash report syntax errors when my C News scripts use a
94 redirection before a subshell command?
95 F6) Why can't I use vi-mode editing on Red Hat Linux 6.1?
96 F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on
99 Section G: How can I get bash to do certain common things?
101 G1) How can I get bash to read and display eight-bit characters?
102 G2) How do I write a function `x' to replace builtin command `x', but
103 still invoke the command from within the function?
104 G3) How can I find the value of a shell variable whose name is the value
105 of another shell variable?
106 G4) How can I make the bash `time' reserved word print timing output that
107 looks like the output from my system's /usr/bin/time?
108 G5) How do I get the current directory into my prompt?
109 G6) How can I rename "*.foo" to "*.bar"?
110 G7) How can I translate a filename from uppercase to lowercase?
111 G8) How can I write a filename expansion (globbing) pattern that will match
112 all files in the current directory except "." and ".."?
114 Section H: Where do I go from here?
116 H1) How do I report bugs in bash, and where should I look for fixes and
118 H2) What kind of bash documentation is there?
119 H3) What's coming in future versions?
120 H4) What's on the bash `wish list'?
121 H5) When will the next release appear?
124 Section A: The Basics
128 Bash is a Unix command interpreter (shell). It is an implementation of
129 the Posix 1003.2 shell standard, and resembles the Korn and System V
132 Bash contains a number of enhancements over those shells, both
133 for interactive use and shell programming. Features geared
134 toward interactive use include command line editing, command
135 history, job control, aliases, and prompt expansion. Programming
136 features include additional variable expansions, shell
137 arithmetic, and a number of variables and options to control
140 Bash was originally written by Brian Fox of the Free Software
141 Foundation. The current developer and maintainer is Chet Ramey
142 of Case Western Reserve University.
144 A2) What's the latest version?
146 The latest version is 4.0, first made available on 20 February, 2009.
148 A3) Where can I get it?
150 Bash is the GNU project's shell, and so is available from the
151 master GNU archive site, ftp.gnu.org, and its mirrors. The
152 latest version is also available for FTP from ftp.cwru.edu.
153 The following URLs tell how to get version 4.0:
155 ftp://ftp.gnu.org/pub/gnu/bash/bash-4.0.tar.gz
156 ftp://ftp.cwru.edu/pub/bash/bash-4.0.tar.gz
158 Formatted versions of the documentation are available with the URLs:
160 ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-4.0.tar.gz
161 ftp://ftp.cwru.edu/pub/bash/bash-doc-4.0.tar.gz
163 Any patches for the current version are available with the URL:
165 ftp://ftp.cwru.edu/pub/bash/bash-4.0-patches/
167 A4) On what machines will bash run?
169 Bash has been ported to nearly every version of Unix. All you
170 should have to do to build it on a machine for which a port
171 exists is to type `configure' and then `make'. The build process
172 will attempt to discover the version of Unix you have and tailor
173 itself accordingly, using a script created by GNU autoconf.
175 More information appears in the file `INSTALL' in the distribution.
177 The Bash web page (http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html)
178 explains how to obtain binary versions of bash for most of the major
179 commercial Unix systems.
181 A5) Will bash run on operating systems other than Unix?
183 Configuration specifics for Unix-like systems such as QNX and
184 LynxOS are included in the distribution. Bash-2.05 and later
185 versions should compile and run on Minix 2.0 (patches were
186 contributed), but I don't believe anyone has built bash-2.x on
187 earlier Minix versions yet.
189 Bash has been ported to versions of Windows implementing the Win32
190 programming interface. This includes Windows 95 and Windows NT.
191 The port was done by Cygnus Solutions (now part of Red Hat) as part
192 of their CYGWIN project. For more information about the project, see
193 http://www.cygwin.com/.
195 Cygnus originally ported bash-1.14.7, and that port was part of their
196 early GNU-Win32 (the original name) releases. Cygnus has also done
197 ports of bash-2.05b and bash-3.2 to the CYGWIN environment, and both
198 are available as part of their current release.
200 Bash-2.05b and later versions should require no local Cygnus changes to
201 build and run under CYGWIN.
203 DJ Delorie has a port of bash-2.x which runs under MS-DOS, as part
204 of the DJGPP project. For more information on the project, see
206 http://www.delorie.com/djgpp/
208 I have been told that the original DJGPP port was done by Daisuke Aoyama.
210 Mark Elbrecht <snowball3@bigfoot.com> has sent me notice that bash-2.04
211 is available for DJGPP V2. The files are available as:
213 ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204b.zip binary
214 ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204d.zip documentation
215 ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204s.zip source
217 Mark began to work with bash-2.05, but I don't know the current status.
219 Bash-3.0 compiles and runs with no modifications under Microsoft's Services
220 for Unix (SFU), once known as Interix. I do not anticipate any problems
221 with building bash-4.0, but will gladly accept any patches that are needed.
223 A6) How can I build bash with gcc?
225 Bash configures to use gcc by default if it is available. Read the
226 file INSTALL in the distribution for more information.
228 A7) How can I make bash my login shell?
230 Some machines let you use `chsh' to change your login shell. Other
231 systems use `passwd -s' or `passwd -e'. If one of these works for
232 you, that's all you need. Note that many systems require the full
233 pathname to a shell to appear in /etc/shells before you can make it
234 your login shell. For this, you may need the assistance of your
235 friendly local system administrator.
237 If you cannot do this, you can still use bash as your login shell, but
238 you need to perform some tricks. The basic idea is to add a command
239 to your login shell's startup file to replace your login shell with
242 For example, if your login shell is csh or tcsh, and you have installed
243 bash in /usr/gnu/bin/bash, add the following line to ~/.login:
245 if ( -f /usr/gnu/bin/bash ) exec /usr/gnu/bin/bash --login
247 (the `--login' tells bash that it is a login shell).
249 It's not a good idea to put this command into ~/.cshrc, because every
250 csh you run without the `-f' option, even ones started to run csh scripts,
251 reads that file. If you must put the command in ~/.cshrc, use something
254 if ( $?prompt ) exec /usr/gnu/bin/bash --login
256 to ensure that bash is exec'd only when the csh is interactive.
258 If your login shell is sh or ksh, you have to do two things.
260 First, create an empty file in your home directory named `.bash_profile'.
261 The existence of this file will prevent the exec'd bash from trying to
262 read ~/.profile, and re-execing itself over and over again. ~/.bash_profile
263 is the first file bash tries to read initialization commands from when
264 it is invoked as a login shell.
266 Next, add a line similar to the above to ~/.profile:
268 [ -f /usr/gnu/bin/bash ] && [ -x /usr/gnu/bin/bash ] && \
269 exec /usr/gnu/bin/bash --login
271 This will cause login shells to replace themselves with bash running as
272 a login shell. Once you have this working, you can copy your initialization
273 code from ~/.profile to ~/.bash_profile.
275 I have received word that the recipe supplied above is insufficient for
276 machines running CDE. CDE has a maze of twisty little startup files, all
279 If you cannot change your login shell in the password file to bash, you
280 will have to (apparently) live with CDE using the shell in the password
281 file to run its startup scripts. If you have changed your shell to bash,
282 there is code in the CDE startup files (on Solaris, at least) that attempts
283 to do the right thing. It is, however, often broken, and may require that
284 you use the $BASH_ENV trick described below.
286 `dtterm' claims to use $SHELL as the default program to start, so if you
287 can change $SHELL in the CDE startup files, you should be able to use bash
288 in your terminal windows.
290 Setting DTSOURCEPROFILE in ~/.dtprofile will cause the `Xsession' program
291 to read your login shell's startup files. You may be able to use bash for
292 the rest of the CDE programs by setting SHELL to bash in ~/.dtprofile as
293 well, but I have not tried this.
295 You can use the above `exec' recipe to start bash when not logging in with
296 CDE by testing the value of the DT variable:
298 if [ -n "$DT" ]; then
299 [ -f /usr/gnu/bin/bash ] && exec /usr/gnu/bin/bash --login
302 If CDE starts its shells non-interactively during login, the login shell
303 startup files (~/.profile, ~/.bash_profile) will not be sourced at login.
304 To get around this problem, append a line similar to the following to your
307 BASH_ENV=${HOME}/.bash_profile ; export BASH_ENV
309 and add the following line to the beginning of ~/.bash_profile:
313 A8) I just changed my login shell to bash, and now I can't FTP into my
316 You must add the full pathname to bash to the file /etc/shells. As
317 noted in the answer to the previous question, many systems require
318 this before you can make bash your login shell.
320 Most versions of ftpd use this file to prohibit `special' users
321 such as `uucp' and `news' from using FTP.
323 A9) What's the `POSIX Shell and Utilities standard'?
325 POSIX is a name originally coined by Richard Stallman for a
326 family of open system standards based on UNIX. There are a
327 number of aspects of UNIX under consideration for
328 standardization, from the basic system services at the system
329 call and C library level to applications and tools to system
330 administration and management. Each area of standardization is
331 assigned to a working group in the 1003 series.
333 The POSIX Shell and Utilities standard was originally developed by
334 IEEE Working Group 1003.2 (POSIX.2). Today it has been merged with
335 the original 1003.1 Working Group and is maintained by the Austin
336 Group (a joint working group of the IEEE, The Open Group and
337 ISO/IEC SC22/WG15). Today the Shell and Utilities are a volume
338 within the set of documents that make up IEEE Std 1003.1-2001, and
339 thus now the former POSIX.2 (from 1992) is now part of the current
340 POSIX.1 standard (POSIX 1003.1-2001).
342 The Shell and Utilities volume concentrates on the command
343 interpreter interface and utility programs commonly executed from
344 the command line or by other programs. The standard is freely
345 available on the web at http://www.UNIX-systems.org/version3/ .
346 Work continues at the Austin Group on maintenance issues; see
347 http://www.opengroup.org/austin/ to join the discussions.
349 Bash is concerned with the aspects of the shell's behavior defined
350 by the POSIX Shell and Utilities volume. The shell command
351 language has of course been standardized, including the basic flow
352 control and program execution constructs, I/O redirection and
353 pipelining, argument handling, variable expansion, and quoting.
355 The `special' builtins, which must be implemented as part of the
356 shell to provide the desired functionality, are specified as
357 being part of the shell; examples of these are `eval' and
358 `export'. Other utilities appear in the sections of POSIX not
359 devoted to the shell which are commonly (and in some cases must
360 be) implemented as builtin commands, such as `read' and `test'.
361 POSIX also specifies aspects of the shell's interactive
362 behavior as part of the UPE, including job control and command
363 line editing. Only vi-style line editing commands have been
364 standardized; emacs editing commands were left out due to
367 The latest version of the POSIX Shell and Utilities standard is
368 available (now updated to the 2004 Edition) as part of the Single
369 UNIX Specification Version 3 at
371 http://www.UNIX-systems.org/version3/
373 A10) What is the bash `posix mode'?
375 Although bash is an implementation of the POSIX shell
376 specification, there are areas where the bash default behavior
377 differs from that spec. The bash `posix mode' changes the bash
378 behavior in these areas so that it obeys the spec more closely.
380 Posix mode is entered by starting bash with the --posix or
381 '-o posix' option or executing `set -o posix' after bash is running.
383 The specific aspects of bash which change when posix mode is
384 active are listed in the file POSIX in the bash distribution.
385 They are also listed in a section in the Bash Reference Manual
386 (from which that file is generated).
388 Section B: The latest version
390 B1) What's new in version 4.0?
392 Bash-4.0 is the fourth major release of bash. There are numerous new features,
393 some experimental. Depending on community reception, the experimental
394 features will evolve.
396 Bash-4.0 contains the following new features (see the manual page for
397 complete descriptions and the CHANGES and NEWS files in the bash-4.0
400 o When using substring expansion on the positional parameters, a starting
401 index of 0 now causes $0 to be prefixed to the list.
403 o There is a new variable, $BASHPID, which always returns the process id of
406 o There is a new `autocd' option that, when enabled, causes bash to attempt
407 to `cd' to a directory name that is supplied as the first word of a
410 o There is a new `checkjobs' option that causes the shell to check for and
411 report any running or stopped jobs at exit.
413 o The programmable completion code exports a new COMP_TYPE variable, set to
414 a character describing the type of completion being attempted.
416 o The programmable completion code exports a new COMP_KEY variable, set to
417 the character that caused the completion to be invoked (e.g., TAB).
419 o The programmable completion code now uses the same set of characters as
420 readline when breaking the command line into a list of words.
422 o The block multiplier for the ulimit -c and -f options is now 512 when in
423 Posix mode, as Posix specifies.
425 o Changed the behavior of the read builtin to save any partial input received
426 in the specified variable when the read builtin times out. This also
427 results in variables specified as arguments to read to be set to the empty
428 string when there is no input available. When the read builtin times out,
429 it returns an exit status greater than 128.
431 o The shell now has the notion of a `compatibility level', controlled by
432 new variables settable by `shopt'. Setting this variable currently
433 restores the bash-3.1 behavior when processing quoted strings on the rhs
434 of the `=~' operator to the `[[' command.
436 o The `ulimit' builtin now has new -b (socket buffer size) and -T (number
439 o There is a new `compopt' builtin that allows completion functions to modify
440 completion options for existing completions or the completion currently
443 o The `read' builtin has a new -i option which inserts text into the reply
444 buffer when using readline.
446 o A new `-E' option to the complete builtin allows control of the default
447 behavior for completion on an empty line.
449 o There is now limited support for completing command name words containing
452 o The `help' builtin now has a new -d option, to display a short description,
453 and a -m option, to print help information in a man page-like format.
455 o There is a new `mapfile' builtin to populate an array with lines from a
458 o If a command is not found, the shell attempts to execute a shell function
459 named `command_not_found_handle', supplying the command words as the
462 o There is a new shell option: `globstar'. When enabled, the globbing code
463 treats `**' specially -- it matches all directories (and files within
464 them, when appropriate) recursively.
466 o There is a new shell option: `dirspell'. When enabled, the filename
467 completion code performs spelling correction on directory names during
470 o The `-t' option to the `read' builtin now supports fractional timeout
473 o Brace expansion now allows zero-padding of expanded numeric values and
474 will add the proper number of zeroes to make sure all values contain the
475 same number of digits.
477 o There is a new bash-specific bindable readline function: `dabbrev-expand'.
478 It uses menu completion on a set of words taken from the history list.
480 o The command assigned to a key sequence with `bind -x' now sets two new
481 variables in the environment of the executed command: READLINE_LINE_BUFFER
482 and READLINE_POINT. The command can change the current readline line
483 and cursor position by modifying READLINE_LINE_BUFFER and READLINE_POINT,
486 o There is a new >>& redirection operator, which appends the standard output
487 and standard error to the named file.
489 o The parser now understands `|&' as a synonym for `2>&1 |', which redirects
490 the standard error for a command through a pipe.
492 o The new `;&' case statement action list terminator causes execution to
493 continue with the action associated with the next pattern in the
494 statement rather than terminating the command.
496 o The new `;;&' case statement action list terminator causes the shell to
497 test the next set of patterns after completing execution of the current
498 action, rather than terminating the command.
500 o The shell understands a new variable: PROMPT_DIRTRIM. When set to an
501 integer value greater than zero, prompt expansion of \w and \W will
502 retain only that number of trailing pathname components and replace
503 the intervening characters with `...'.
505 o There are new case-modifying word expansions: uppercase (^[^]) and
506 lowercase (,[,]). They can work on either the first character or
507 array element, or globally. They accept an optional shell pattern
508 that determines which characters to modify. There is an optionally-
509 configured feature to include capitalization operators.
511 o The shell provides associative array variables, with the appropriate
512 support to create, delete, assign values to, and expand them.
514 o The `declare' builtin now has new -l (convert value to lowercase upon
515 assignment) and -u (convert value to uppercase upon assignment) options.
516 There is an optionally-configurable -c option to capitalize a value at
519 o There is a new `coproc' reserved word that specifies a coprocess: an
520 asynchronous command run with two pipes connected to the creating shell.
521 Coprocs can be named. The input and output file descriptors and the
522 PID of the coprocess are available to the calling shell in variables
523 with coproc-specific names.
525 o A value of 0 for the -t option to `read' now returns success if there is
526 input available to be read from the specified file descriptor.
528 o CDPATH and GLOBIGNORE are ignored when the shell is running in privileged
531 o New bindable readline functions shell-forward-word and shell-backward-word,
532 which move forward and backward words delimited by shell metacharacters
533 and honor shell quoting.
535 o New bindable readline functions shell-backward-kill-word and shell-kill-word
536 which kill words backward and forward, but use the same word boundaries
537 as shell-forward-word and shell-backward-word.
539 A short feature history dating from Bash-2.0:
541 Bash-3.2 contained the following new features:
543 o Bash-3.2 now checks shell scripts for NUL characters rather than non-printing
544 characters when deciding whether or not a script is a binary file.
546 o Quoting the string argument to the [[ command's =~ (regexp) operator now
547 forces string matching, as with the other pattern-matching operators.
549 Bash-3.1 contained the following new features:
551 o Bash-3.1 may now be configured and built in a mode that enforces strict
554 o The `+=' assignment operator, which appends to the value of a string or
555 array variable, has been implemented.
557 o It is now possible to ignore case when matching in contexts other than
558 filename generation using the new `nocasematch' shell option.
560 Bash-3.0 contained the following new features:
562 o Features to support the bash debugger have been implemented, and there
563 is a new `extdebug' option to turn the non-default options on
565 o HISTCONTROL is now a colon-separated list of options and has been
566 extended with a new `erasedups' option that will result in only one
567 copy of a command being kept in the history list
569 o Brace expansion has been extended with a new {x..y} form, producing
570 sequences of digits or characters
572 o Timestamps are now kept with history entries, with an option to save
573 and restore them from the history file; there is a new HISTTIMEFORMAT
574 variable describing how to display the timestamps when listing history
577 o The `[[' command can now perform extended regular expression (egrep-like)
578 matching, with matched subexpressions placed in the BASH_REMATCH array
581 o A new `pipefail' option causes a pipeline to return a failure status if
582 any command in it fails
584 o The `jobs', `kill', and `wait' builtins now accept job control notation
585 in their arguments even if job control is not enabled
587 o The `gettext' package and libintl have been integrated, and the shell
588 messages may be translated into other languages
590 Bash-2.05b introduced the following new features:
592 o support for multibyte characters has been added to both bash and readline
594 o the DEBUG trap is now run *before* simple commands, ((...)) commands,
595 [[...]] conditional commands, and for ((...)) loops
597 o the shell now performs arithmetic in the largest integer size the machine
600 o there is a new \D{...} prompt expansion; passes the `...' to strftime(3)
601 and inserts the result into the expanded prompt
603 o there is a new `here-string' redirection operator: <<< word
605 o when displaying variables, function attributes and definitions are shown
606 separately, allowing them to be re-used as input (attempting to re-use
607 the old output would result in syntax errors).
609 o `read' has a new `-u fd' option to read from a specified file descriptor
611 o the bash debugger in examples/bashdb has been modified to work with the
612 new DEBUG trap semantics, the command set has been made more gdb-like,
613 and the changes to $LINENO make debugging functions work better
615 o the expansion of $LINENO inside a shell function is only relative to the
616 function start if the shell is interactive -- if the shell is running a
617 script, $LINENO expands to the line number in the script. This is as
620 Bash-2.05a introduced the following new features:
622 o The `printf' builtin has undergone major work
624 o There is a new read-only `shopt' option: login_shell, which is set by
625 login shells and unset otherwise
627 o New `\A' prompt string escape sequence; expanding to time in 24-hour
630 o New `-A group/-g' option to complete and compgen; goes group name
633 o New [+-]O invocation option to set and unset `shopt' options at startup
635 o ksh-like `ERR' trap
637 o `for' loops now allow empty word lists after the `in' reserved word
639 o new `hard' and `soft' arguments for the `ulimit' builtin
641 o Readline can be configured to place the user at the same point on the line
642 when retrieving commands from the history list
644 o Readline can be configured to skip `hidden' files (filenames with a leading
645 `.' on Unix) when performing completion
647 Bash-2.05 introduced the following new features:
649 o This version has once again reverted to using locales and strcoll(3) when
650 processing pattern matching bracket expressions, as POSIX requires.
651 o Added a new `--init-file' invocation argument as a synonym for `--rcfile',
652 per the new GNU coding standards.
653 o The /dev/tcp and /dev/udp redirections now accept service names as well as
655 o `complete' and `compgen' now take a `-o value' option, which controls some
656 of the aspects of that compspec. Valid values are:
658 default - perform bash default completion if programmable
659 completion produces no matches
660 dirnames - perform directory name completion if programmable
661 completion produces no matches
662 filenames - tell readline that the compspec produces filenames,
663 so it can do things like append slashes to
664 directory names and suppress trailing spaces
665 o A new loadable builtin, realpath, which canonicalizes and expands symlinks
666 in pathname arguments.
667 o When `set' is called without options, it prints function defintions in a
668 way that allows them to be reused as input. This affects `declare' and
669 `declare -p' as well. This only happens when the shell is not in POSIX
670 mode, since POSIX.2 forbids this behavior.
672 Bash-2.04 introduced the following new features:
674 o Programmable word completion with the new `complete' and `compgen' builtins;
675 examples are provided in examples/complete/complete-examples
676 o `history' has a new `-d' option to delete a history entry
677 o `bind' has a new `-x' option to bind key sequences to shell commands
678 o The prompt expansion code has new `\j' and `\l' escape sequences
679 o The `no_empty_cmd_completion' shell option, if enabled, inhibits
680 command completion when TAB is typed on an empty line
681 o `help' has a new `-s' option to print a usage synopsis
682 o New arithmetic operators: var++, var--, ++var, --var, expr1,expr2 (comma)
683 o New ksh93-style arithmetic for command:
684 for ((expr1 ; expr2; expr3 )); do list; done
685 o `read' has new options: `-t', `-n', `-d', `-s'
686 o The redirection code handles several filenames specially: /dev/fd/N,
687 /dev/stdin, /dev/stdout, /dev/stderr
688 o The redirection code now recognizes /dev/tcp/HOST/PORT and
689 /dev/udp/HOST/PORT and tries to open a TCP or UDP socket, respectively,
690 to the specified port on the specified host
691 o The ${!prefix*} expansion has been implemented
692 o A new FUNCNAME variable, which expands to the name of a currently-executing
694 o The GROUPS variable is no longer readonly
695 o A new shopt `xpg_echo' variable, to control the behavior of echo with
696 respect to backslash-escape sequences at runtime
697 o The NON_INTERACTIVE_LOGIN_SHELLS #define has returned
699 The version of Readline released with Bash-2.04, Readline-4.1, had several
700 new features as well:
702 o Parentheses matching is always compiled into readline, and controllable
703 with the new `blink-matching-paren' variable
704 o The history-search-forward and history-search-backward functions now leave
705 point at the end of the line when the search string is empty, like
706 reverse-search-history, and forward-search-history
707 o A new function for applications: rl_on_new_line_with_prompt()
708 o New variables for applications: rl_already_prompted, and rl_gnu_readline_p
711 Bash-2.03 had very few new features, in keeping with the convention
712 that odd-numbered releases provide mainly bug fixes. A number of new
713 features were added to Readline, mostly at the request of the Cygnus
716 A new shopt option, `restricted_shell', so that startup files can test
717 whether or not the shell was started in restricted mode
718 Filename generation is now performed on the words between ( and ) in
719 compound array assignments (this is really a bug fix)
720 OLDPWD is now auto-exported, as POSIX.2 requires
721 ENV and BASH_ENV are read-only variables in a restricted shell
722 Bash may now be linked against an already-installed Readline library,
723 as long as the Readline library is version 4 or newer
724 All shells begun with the `--login' option will source the login shell
725 startup files, even if the shell is not interactive
727 There were lots of changes to the version of the Readline library released
728 along with Bash-2.03. For a complete list of the changes, read the file
729 CHANGES in the Bash-2.03 distribution.
731 Bash-2.02 contained the following new features:
733 a new version of malloc (based on the old GNU malloc code in previous
734 bash versions) that is more page-oriented, more conservative
735 with memory usage, does not `orphan' large blocks when they
736 are freed, is usable on 64-bit machines, and has allocation
737 checking turned on unconditionally
738 POSIX.2-style globbing character classes ([:alpha:], [:alnum:], etc.)
739 POSIX.2-style globbing equivalence classes
740 POSIX.2-style globbing collating symbols
741 the ksh [[...]] extended conditional command
742 the ksh egrep-style extended pattern matching operators
743 a new `printf' builtin
744 the ksh-like $(<filename) command substitution, which is equivalent to
746 new tilde prefixes that expand to directories from the directory stack
747 new `**' arithmetic operator to do exponentiation
748 case-insensitive globbing (filename expansion)
749 menu completion a la tcsh
750 `magic-space' history expansion function like tcsh
751 the readline inputrc `language' has a new file inclusion directive ($include)
753 Bash-2.01 contained only a few new features:
755 new `GROUPS' builtin array variable containing the user's group list
756 new bindable readline commands: history-and-alias-expand-line and
759 Bash-2.0 contained extensive changes and new features from bash-1.14.7.
762 new `time' reserved word to time pipelines, shell builtins, and
764 one-dimensional arrays with a new compound assignment statement,
765 appropriate expansion constructs and modifications to some
766 of the builtins (read, declare, etc.) to use them
767 new quoting syntaxes for ANSI-C string expansion and locale-specific
769 new expansions to do substring extraction, pattern replacement, and
770 indirect variable expansion
771 new builtins: `disown' and `shopt'
772 new variables: HISTIGNORE, SHELLOPTS, PIPESTATUS, DIRSTACK, GLOBIGNORE,
773 MACHTYPE, BASH_VERSINFO
774 special handling of many unused or redundant variables removed
775 (e.g., $notify, $glob_dot_filenames, $no_exit_on_failed_exec)
776 dynamic loading of new builtin commands; many loadable examples provided
777 new prompt expansions: \a, \e, \n, \H, \T, \@, \v, \V
778 history and aliases available in shell scripts
779 new readline variables: enable-keypad, mark-directories, input-meta,
780 visible-stats, disable-completion, comment-begin
781 new readline commands to manipulate the mark and operate on the region
782 new readline emacs mode commands and bindings for ksh-88 compatibility
783 updated and extended builtins
785 expanded (and now documented) restricted shell mode
787 implementation stuff:
788 autoconf-based configuration
789 nearly all of the bugs reported since version 1.14 have been fixed
790 most builtins converted to use builtin `getopt' for consistency
791 most builtins use -p option to display output in a reusable form
793 grammar tighter and smaller (66 reduce-reduce conflicts gone)
794 lots of code now smaller and faster
795 test suite greatly expanded
797 B2) Are there any user-visible incompatibilities between bash-4.0, bash-3.2,
800 There are a few incompatibilities between version 4.0 and version 3.2.
801 They are detailed in the file COMPAT in the bash distribution. That file
802 is not meant to be all-encompassing; send mail to bash-maintainers@gnu.org
803 if if you find something that's not mentioned there.
805 Section C: Differences from other Unix shells
807 C1) How does bash differ from sh, the Bourne shell?
809 This is a non-comprehensive list of features that differentiate bash
810 from the SVR4.2 shell. The bash manual page explains these more
813 Things bash has that sh does not:
814 long invocation options
815 [+-]O invocation option
817 `!' reserved word to invert pipeline return value
818 `time' reserved word to time pipelines and shell builtins
819 the `function' reserved word
820 the `select' compound command and reserved word
821 arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done
822 new $'...' and $"..." quoting
823 the $(...) form of command substitution
824 the $(<filename) form of command substitution, equivalent to
826 the ${#param} parameter value length operator
827 the ${!param} indirect parameter expansion operator
828 the ${!param*} prefix expansion operator
829 the ${param:offset[:length]} parameter substring operator
830 the ${param/pat[/string]} parameter pattern substitution operator
831 expansions to perform substring removal (${p%[%]w}, ${p#[#]w})
832 expansion of positional parameters beyond $9 with ${num}
833 variables: BASH, BASHPID, BASH_VERSION, BASH_VERSINFO, UID, EUID, REPLY,
834 TIMEFORMAT, PPID, PWD, OLDPWD, SHLVL, RANDOM, SECONDS,
835 LINENO, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, HOSTNAME,
836 ENV, PS3, PS4, DIRSTACK, PIPESTATUS, HISTSIZE, HISTFILE,
837 HISTFILESIZE, HISTCONTROL, HISTIGNORE, GLOBIGNORE, GROUPS,
838 PROMPT_COMMAND, FCEDIT, FIGNORE, IGNOREEOF, INPUTRC,
839 SHELLOPTS, OPTERR, HOSTFILE, TMOUT, FUNCNAME, histchars,
840 auto_resume, PROMPT_DIRTRIM
843 variable arrays with new compound assignment syntax
844 redirections: <>, &>, >|, <<<, [n]<&word-, [n]>&word-, >>&
845 prompt string special char translation and variable expansion
846 auto-export of variables in initial environment
847 command search finds functions before builtins
848 bash return builtin will exit a file sourced with `.'
849 builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -d/-l/-p/-t.
850 export -n/-f/-p/name=value, pwd -L/-P,
851 read -e/-p/-a/-t/-n/-d/-s/-u/-i,
852 readonly -a/-f/name=value, trap -l, set +o,
853 set -b/-m/-o option/-h/-p/-B/-C/-H/-P,
854 unset -f/-v, ulimit -i/-m/-p/-q/-u/-x,
855 type -a/-p/-t/-f/-P, suspend -f, kill -n,
856 test -o optname/s1 == s2/s1 < s2/s1 > s2/-nt/-ot/-ef/-O/-G/-S
857 bash reads ~/.bashrc for interactive shells, $ENV for non-interactive
858 bash restricted shell mode is more extensive
859 bash allows functions and variables with the same name
862 arithmetic expansion with $((...)) and `let' builtin
863 the `[[...]]' extended conditional command
865 aliases and alias/unalias builtins
866 local variables in functions and `local' builtin
867 readline and command-line editing with programmable completion
868 command history and history/fc builtins
869 csh-like history expansion
870 other new bash builtins: bind, command, compgen, complete, builtin,
871 declare/typeset, dirs, enable, fc, help,
872 history, logout, popd, pushd, disown, shopt,
873 printf, compopt, mapfile
875 filename generation when using output redirection (command >a*)
876 POSIX.2-style globbing character classes
877 POSIX.2-style globbing equivalence classes
878 POSIX.2-style globbing collating symbols
879 egrep-like extended pattern matching operators
880 case-insensitive pattern matching and globbing
881 variable assignments preceding commands affect only that command,
882 even for builtins and functions
883 posix mode and strict posix conformance
884 redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr,
885 /dev/tcp/host/port, /dev/udp/host/port
886 debugger support, including `caller' builtin and new variables
888 the `+=' assignment operator
889 autocd shell option and behavior
890 command-not-found hook with command_not_found_handle shell function
891 globstar shell option and `**' globbing behavior
892 |& synonym for `2>&1 |'
893 ;& and ;;& case action list terminators
894 case-modifying word expansions and variable attributes
896 coprocesses using the `coproc' reserved word and variables
898 Things sh has that bash does not:
899 uses variable SHACCT to do shell accounting
900 includes `stop' builtin (bash can use alias stop='kill -s STOP')
902 turns on job control if called as `jsh'
903 $TIMEOUT (like bash $TMOUT)
904 `^' is a synonym for `|'
905 new SVR4.2 sh builtins: mldmode, priv
907 Implementation differences:
908 redirection to/from compound commands causes sh to create a subshell
909 bash does not allow unbalanced quotes; sh silently inserts them at EOF
910 bash does not mess with signal 11
911 sh sets (euid, egid) to (uid, gid) if -p not supplied and uid < 100
912 bash splits only the results of expansions on IFS, using POSIX.2
913 field splitting rules; sh splits all words on IFS
914 sh does not allow MAILCHECK to be unset (?)
915 sh does not allow traps on SIGALRM or SIGCHLD
916 bash allows multiple option arguments when invoked (e.g. -x -v);
917 sh allows only a single option argument (`sh -x -v' attempts
918 to open a file named `-v', and, on SunOS 4.1.4, dumps core.
919 On Solaris 2.4 and earlier versions, sh goes into an infinite
921 sh exits a script if any builtin fails; bash exits only if one of
922 the POSIX.2 `special' builtins fails
924 C2) How does bash differ from the Korn shell, version ksh88?
926 Things bash has or uses that ksh88 does not:
927 long invocation options
928 [-+]O invocation option
931 arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done
932 arithmetic in largest machine-supported size (intmax_t)
933 posix mode and posix conformance
935 tilde expansion for assignment statements that look like $PATH
936 process substitution with named pipes if /dev/fd is not available
937 the ${!param} indirect parameter expansion operator
938 the ${!param*} prefix expansion operator
939 the ${param:offset[:length]} parameter substring operator
940 the ${param/pat[/string]} parameter pattern substitution operator
941 variables: BASH, BASH_VERSION, BASH_VERSINFO, BASHPID, UID, EUID, SHLVL,
942 TIMEFORMAT, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE,
943 HISTFILESIZE, HISTIGNORE, HISTCONTROL, PROMPT_COMMAND,
944 IGNOREEOF, FIGNORE, INPUTRC, HOSTFILE, DIRSTACK,
945 PIPESTATUS, HOSTNAME, OPTERR, SHELLOPTS, GLOBIGNORE,
946 GROUPS, FUNCNAME, histchars, auto_resume, PROMPT_DIRTRIM
947 prompt expansion with backslash escapes and command substitution
948 redirection: &> (stdout and stderr), <<<, [n]<&word-, [n]>&word-, >>&
949 more extensive and extensible editing and programmable completion
950 builtins: bind, builtin, command, declare, dirs, echo -e/-E, enable,
951 exec -l/-c/-a, fc -s, export -n/-f/-p, hash, help, history,
952 jobs -x/-r/-s, kill -s/-n/-l, local, logout, popd, pushd,
953 read -e/-p/-a/-t/-n/-d/-s, readonly -a/-n/-f/-p,
954 set -o braceexpand/-o histexpand/-o interactive-comments/
955 -o notify/-o physical/-o posix/-o hashall/-o onecmd/
956 -h/-B/-C/-b/-H/-P, set +o, suspend, trap -l, type,
957 typeset -a/-F/-p, ulimit -i/-q/-u/-x, umask -S, alias -p,
958 shopt, disown, printf, complete, compgen, compopt, mapfile
959 `!' csh-style history expansion
960 POSIX.2-style globbing character classes
961 POSIX.2-style globbing equivalence classes
962 POSIX.2-style globbing collating symbols
963 egrep-like extended pattern matching operators
964 case-insensitive pattern matching and globbing
965 `**' arithmetic operator to do exponentiation
966 redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr
967 arrays of unlimited size
968 TMOUT is default timeout for `read' and `select'
969 debugger support, including the `caller' builtin
971 Timestamps in history entries
972 {x..y} brace expansion
973 The `+=' assignment operator
974 autocd shell option and behavior
975 command-not-found hook with command_not_found_handle shell function
976 globstar shell option and `**' globbing behavior
977 |& synonym for `2>&1 |'
978 ;& and ;;& case action list terminators
979 case-modifying word expansions and variable attributes
981 coprocesses using the `coproc' reserved word and variables
983 Things ksh88 has or uses that bash does not:
984 tracked aliases (alias -t)
985 variables: ERRNO, FPATH, EDITOR, VISUAL
986 co-processes (bash uses different syntax)
987 weirdly-scoped functions
988 typeset +f to list all function names without definitions
989 text of command history kept in a file, not memory
990 builtins: alias -x, cd old new, newgrp, print,
991 read -p/-s/var?prompt, set -A/-o gmacs/
992 -o bgnice/-o markdirs/-o trackall/-o viraw/-s,
993 typeset -H/-L/-R/-Z/-A/-ft/-fu/-fx/-t, whence
994 using environment to pass attributes of exported variables
995 arithmetic evaluation done on arguments to some builtins
996 reads .profile from $PWD when invoked as login shell
998 Implementation differences:
999 ksh runs last command of a pipeline in parent shell context
1000 bash has brace expansion by default (ksh88 compile-time option)
1001 bash has fixed startup file for all interactive shells; ksh reads $ENV
1002 bash has exported functions
1003 bash command search finds functions before builtins
1004 bash waits for all commands in pipeline to exit before returning status
1005 emacs-mode editing has some slightly different key bindings
1007 C3) Which new features in ksh-93 are not in bash, and which are?
1009 This list is current through ksh93t (11/04/2008)
1011 New things in ksh-93 not in bash-4.0:
1012 floating point arithmetic and variables
1013 math library functions
1014 ${!name[sub]} name of subscript for associative array
1015 `.' is allowed in variable names to create a hierarchical namespace
1016 more extensive compound assignment syntax
1017 discipline functions
1019 variables: .sh.edchar, .sh.edmode, .sh.edcol, .sh.edtext, .sh.version,
1020 .sh.name, .sh.subscript, .sh.value, .sh.match, HISTEDIT
1021 backreferences in pattern matching (\N)
1022 `&' operator in pattern lists for matching (match all instead of any)
1023 exit statuses between 0 and 255
1024 FPATH and PATH mixing
1025 lexical scoping for local variables in `ksh' functions
1026 no scoping for local variables in `POSIX' functions
1027 $'' \C[.collating-element.] escape sequence
1028 -C/-I invocation options
1029 print -f (bash uses printf)
1030 `fc' has been renamed to `hist'
1031 `.' can execute shell functions
1033 printf %B, %H, %P, %R, %T, %Z modifiers, output base for %d, `=' flag
1034 read -N (read -n differs, too)/-v
1035 set -o showme/-o multiline (bash default)
1036 `sleep' and `getconf' builtins (bash has loadable versions)
1037 typeset -n and `nameref' variables
1038 typeset -C/-S/-T/-X/-h/-s
1039 experimental `type' definitions (a la typedef) using typeset
1040 negative subscripts for indexed array variables
1041 array expansions ${array[sub1..sub2]} and ${!array[sub1..sub2]}
1042 associative array assignments using `;' as element separator
1043 command substitution $(n<#) expands to current byte offset for fd N
1044 new '${ ' form of command substitution, executed in current shell
1045 new >;/<#pat/<##pat/<#/># redirections
1046 redirection operators preceded with {varname} to store fd number in varname
1047 brace expansion printf-like formats
1049 New things in ksh-93 present in bash-4.0:
1051 [n]<&word- and [n]>&word- redirections (combination dup and close)
1052 for (( expr1; expr2; expr3 )) ; do list; done - arithmetic for command
1053 ?:, ++, --, `expr1 , expr2' arithmetic operators
1054 expansions: ${!param}, ${param:offset[:len]}, ${param/pat[/str]},
1056 compound array assignment
1057 the `!' reserved word
1058 loadable builtins -- but ksh uses `builtin' while bash uses `enable'
1059 new $'...' and $"..." quoting
1060 FIGNORE (but bash uses GLOBIGNORE), HISTCMD
1061 brace expansion and set -B
1062 changes to kill builtin
1063 `command', `builtin', `disown' builtins
1066 read -A (bash uses read -a)
1069 `.' restores the positional parameters when it completes
1072 set -G (-o globstar) and **
1076 command and arithmetic substitution performed on PS1, PS4, and ENV
1077 command name completion, TAB displaying possible completions
1078 ENV processed only for interactive shells
1079 The `+=' assignment operator
1080 the `;&' case statement "fallthrough" pattern list terminator
1081 csh-style history expansion and set -H
1082 negative offsets in ${param:offset:length}
1084 Section D: Why does bash do some things differently than other Unix shells?
1086 D1) Why does bash run a different version of `command' than
1087 `which command' says it will?
1089 On many systems, `which' is actually a csh script that assumes
1090 you're running csh. In tcsh, `which' and its cousin `where'
1091 are builtins. On other Unix systems, `which' is a perl script
1092 that uses the PATH environment variable. Many Linux distributions
1093 use GNU `which', which is a C program that can understand shell
1096 The csh script version reads the csh startup files from your
1097 home directory and uses those to determine which `command' will
1098 be invoked. Since bash doesn't use any of those startup files,
1099 there's a good chance that your bash environment differs from
1100 your csh environment. The bash `type' builtin does everything
1101 `which' does, and will report correct results for the running
1102 shell. If you're really wedded to the name `which', try adding
1103 the following function definition to your .bashrc:
1110 If you're moving from tcsh and would like to bring `where' along
1111 as well, use this function:
1115 builtin type -a "$@"
1118 D2) Why doesn't bash treat brace expansions exactly like csh?
1120 The only difference between bash and csh brace expansion is that
1121 bash requires a brace expression to contain at least one unquoted
1122 comma if it is to be expanded. Any brace-surrounded word not
1123 containing an unquoted comma is left unchanged by the brace
1124 expansion code. This affords the greatest degree of sh
1127 Bash, ksh, zsh, and pd-ksh all implement brace expansion this way.
1129 D3) Why doesn't bash have csh variable modifiers?
1131 Posix has specified a more powerful, albeit somewhat more cryptic,
1132 mechanism cribbed from ksh, and bash implements it.
1135 Remove smallest suffix pattern. The WORD is expanded to produce
1136 a pattern. It then expands to the value of PARAMETER, with the
1137 smallest portion of the suffix matched by the pattern deleted.
1145 Remove largest suffix pattern. The WORD is expanded to produce
1146 a pattern. It then expands to the value of PARAMETER, with the
1147 largest portion of the suffix matched by the pattern deleted.
1154 Remove smallest prefix pattern. The WORD is expanded to produce
1155 a pattern. It then expands to the value of PARAMETER, with the
1156 smallest portion of the prefix matched by the pattern deleted.
1163 Remove largest prefix pattern. The WORD is expanded to produce
1164 a pattern. It then expands to the value of PARAMETER, with the
1165 largest portion of the prefix matched by the pattern deleted.
1184 D4) How can I make my csh aliases work when I convert to bash?
1186 Bash uses a different syntax to support aliases than csh does.
1187 The details can be found in the documentation. We have provided
1188 a shell script which does most of the work of conversion for you;
1189 this script can be found in ./examples/misc/aliasconv.sh. Here is
1192 Start csh in the normal way for you. (e.g., `csh')
1194 Pipe the output of `alias' through `aliasconv.sh', saving the
1195 results into `bash_aliases':
1197 alias | bash aliasconv.sh >bash_aliases
1199 Edit `bash_aliases', carefully reading through any created
1200 functions. You will need to change the names of some csh specific
1201 variables to the bash equivalents. The script converts $cwd to
1202 $PWD, $term to $TERM, $home to $HOME, $user to $USER, and $prompt
1203 to $PS1. You may also have to add quotes to avoid unwanted
1206 For example, the csh alias:
1208 alias cd 'cd \!*; echo $cwd'
1210 is converted to the bash function:
1212 cd () { command cd "$@"; echo $PWD ; }
1214 The only thing that needs to be done is to quote $PWD:
1216 cd () { command cd "$@"; echo "$PWD" ; }
1218 Merge the edited file into your ~/.bashrc.
1220 There is an additional, more ambitious, script in
1221 examples/misc/cshtobash that attempts to convert your entire csh
1222 environment to its bash equivalent. This script can be run as
1223 simply `cshtobash' to convert your normal interactive
1224 environment, or as `cshtobash ~/.login' to convert your login
1227 D5) How can I pipe standard output and standard error from one command to
1228 another, like csh does with `|&'?
1231 command 2>&1 | command2
1233 The key is to remember that piping is performed before redirection, so
1234 file descriptor 1 points to the pipe when it is duplicated onto file
1237 D6) Now that I've converted from ksh to bash, are there equivalents to
1238 ksh features like autoloaded functions and the `whence' command?
1240 There are features in ksh-88 and ksh-93 that do not have direct bash
1241 equivalents. Most, however, can be emulated with very little trouble.
1243 ksh-88 feature Bash equivalent
1244 -------------- ---------------
1245 compiled-in aliases set up aliases in .bashrc; some ksh aliases are
1246 bash builtins (hash, history, type)
1247 coprocesses named pipe pairs (one for read, one for write)
1248 typeset +f declare -F
1249 cd, print, whence function substitutes in examples/functions/kshenv
1250 autoloaded functions examples/functions/autoload is the same as typeset -fu
1251 read var?prompt read -p prompt var
1253 ksh-93 feature Bash equivalent
1254 -------------- ---------------
1255 sleep, getconf Bash has loadable versions in examples/loadables
1256 ${.sh.version} $BASH_VERSION
1261 Section E: How can I get bash to do certain things, and why does bash do
1262 things the way it does?
1264 E1) Why is the bash builtin `test' slightly different from /bin/test?
1266 The specific example used here is [ ! x -o x ], which is false.
1268 Bash's builtin `test' implements the Posix.2 spec, which can be
1269 summarized as follows (the wording is due to David Korn):
1271 Here is the set of rules for processing test arguments.
1274 1 Arg: True iff argument is not null.
1275 2 Args: If first arg is !, True iff second argument is null.
1276 If first argument is unary, then true if unary test is true
1278 3 Args: If second argument is a binary operator, do binary test of $1 $3
1279 If first argument is !, negate two argument test of $2 $3
1280 If first argument is `(' and third argument is `)', do the
1281 one-argument test of the second argument.
1283 4 Args: If first argument is !, negate three argument test of $2 $3 $4.
1284 Otherwise unspecified
1285 5 or more Args: unspecified. (Historical shells would use their
1288 The operators -a and -o are considered binary operators for the purpose
1291 As you can see, the test becomes (not (x or x)), which is false.
1293 E2) Why does bash sometimes say `Broken pipe'?
1295 If a sequence of commands appears in a pipeline, and one of the
1296 reading commands finishes before the writer has finished, the
1297 writer receives a SIGPIPE signal. Many other shells special-case
1298 SIGPIPE as an exit status in the pipeline and do not report it.
1303 `head' can finish before `ps' writes all of its output, and ps
1304 will try to write on a pipe without a reader. In that case, bash
1305 will print `Broken pipe' to stderr when ps is killed by a
1308 As of bash-3.1, bash does not report SIGPIPE errors by default. You
1309 can build a version of bash that will report such errors.
1311 E3) When I have terminal escape sequences in my prompt, why does bash
1312 wrap lines at the wrong column?
1314 Readline, the line editing library that bash uses, does not know
1315 that the terminal escape sequences do not take up space on the
1316 screen. The redisplay code assumes, unless told otherwise, that
1317 each character in the prompt is a `printable' character that
1318 takes up one character position on the screen.
1320 You can use the bash prompt expansion facility (see the PROMPTING
1321 section in the manual page) to tell readline that sequences of
1322 characters in the prompt strings take up no screen space.
1324 Use the \[ escape to begin a sequence of non-printing characters,
1325 and the \] escape to signal the end of such a sequence.
1327 E4) If I pipe the output of a command into `read variable', why doesn't
1328 the output show up in $variable when the read command finishes?
1330 This has to do with the parent-child relationship between Unix
1331 processes. It affects all commands run in pipelines, not just
1332 simple calls to `read'. For example, piping a command's output
1333 into a `while' loop that repeatedly calls `read' will result in
1336 Each element of a pipeline, even a builtin or shell function,
1337 runs in a separate process, a child of the shell running the
1338 pipeline. A subprocess cannot affect its parent's environment.
1339 When the `read' command sets the variable to the input, that
1340 variable is set only in the subshell, not the parent shell. When
1341 the subshell exits, the value of the variable is lost.
1343 Many pipelines that end with `read variable' can be converted
1344 into command substitutions, which will capture the output of
1345 a specified command. The output can then be assigned to a
1348 grep ^gnu /usr/lib/news/active | wc -l | read ngroup
1350 can be converted into
1352 ngroup=$(grep ^gnu /usr/lib/news/active | wc -l)
1354 This does not, unfortunately, work to split the text among
1355 multiple variables, as read does when given multiple variable
1356 arguments. If you need to do this, you can either use the
1357 command substitution above to read the output into a variable
1358 and chop up the variable using the bash pattern removal
1359 expansion operators or use some variant of the following
1362 Say /usr/local/bin/ipaddr is the following shell script:
1365 host `hostname` | awk '/address/ {print $NF}'
1369 /usr/local/bin/ipaddr | read A B C D
1371 to break the local machine's IP address into separate octets, use
1375 set -- $(/usr/local/bin/ipaddr)
1377 A="$1" B="$2" C="$3" D="$4"
1379 Beware, however, that this will change the shell's positional
1380 parameters. If you need them, you should save them before doing
1383 This is the general approach -- in most cases you will not need to
1384 set $IFS to a different value.
1386 Some other user-supplied alternatives include:
1388 read A B C D << HERE
1389 $(IFS=.; echo $(/usr/local/bin/ipaddr))
1392 and, where process substitution is available,
1394 read A B C D < <(IFS=.; echo $(/usr/local/bin/ipaddr))
1396 E5) I have a bunch of shell scripts that use backslash-escaped characters
1397 in arguments to `echo'. Bash doesn't interpret these characters. Why
1398 not, and how can I make it understand them?
1400 This is the behavior of echo on most Unix System V machines.
1402 The bash builtin `echo' is modeled after the 9th Edition
1403 Research Unix version of `echo'. It does not interpret
1404 backslash-escaped characters in its argument strings by default;
1405 it requires the use of the -e option to enable the
1406 interpretation. The System V echo provides no way to disable the
1407 special characters; the bash echo has a -E option to disable
1410 There is a configuration option that will make bash behave like
1411 the System V echo and interpret things like `\t' by default. Run
1412 configure with the --enable-xpg-echo-default option to turn this
1413 on. Be aware that this will cause some of the tests run when you
1414 type `make tests' to fail.
1416 There is a shell option, `xpg_echo', settable with `shopt', that will
1417 change the behavior of echo at runtime. Enabling this option turns
1418 on expansion of backslash-escape sequences.
1420 E6) Why doesn't a while or for loop get suspended when I type ^Z?
1422 This is a consequence of how job control works on Unix. The only
1423 thing that can be suspended is the process group. This is a single
1424 command or pipeline of commands that the shell forks and executes.
1426 When you run a while or for loop, the only thing that the shell forks
1427 and executes are any commands in the while loop test and commands in
1428 the loop bodies. These, therefore, are the only things that can be
1429 suspended when you type ^Z.
1431 If you want to be able to stop the entire loop, you need to put it
1432 within parentheses, which will force the loop into a subshell that
1433 may be stopped (and subsequently restarted) as a single unit.
1435 E7) What about empty for loops in Makefiles?
1437 It's fairly common to see constructs like this in automatically-generated
1445 for d in ${SUBDIRS}; do \
1446 ( cd $$d && ${MAKE} ${MFLAGS} clean ) \
1449 When SUBDIRS is empty, this results in a command like this being passed to
1453 ( cd $d && ${MAKE} ${MFLAGS} clean )
1456 In versions of bash before bash-2.05a, this was a syntax error. If the
1457 reserved word `in' was present, a word must follow it before the semicolon
1458 or newline. The language in the manual page referring to the list of words
1459 being empty referred to the list after it is expanded. These versions of
1460 bash required that there be at least one word following the `in' when the
1461 construct was parsed.
1463 The idiomatic Makefile solution is something like:
1468 subdirs=$SUBDIRS ; for d in $$subdirs; do \
1469 ( cd $$d && ${MAKE} ${MFLAGS} clean ) \
1472 The latest updated POSIX standard has changed this: the word list
1473 is no longer required. Bash versions 2.05a and later accept the
1476 E8) Why does the arithmetic evaluation code complain about `08'?
1478 The bash arithmetic evaluation code (used for `let', $(()), (()), and in
1479 other places), interprets a leading `0' in numeric constants as denoting
1480 an octal number, and a leading `0x' as denoting hexadecimal. This is
1481 in accordance with the POSIX.2 spec, section 2.9.2.1, which states that
1482 arithmetic constants should be handled as signed long integers as defined
1483 by the ANSI/ISO C standard.
1485 The POSIX.2 interpretation committee has confirmed this:
1487 http://www.pasc.org/interps/unofficial/db/p1003.2/pasc-1003.2-173.html
1489 E9) Why does the pattern matching expression [A-Z]* match files beginning
1490 with every letter except `z'?
1492 Bash-2.03, Bash-2.05 and later versions honor the current locale setting
1493 when processing ranges within pattern matching bracket expressions ([A-Z]).
1494 This is what POSIX.2 and SUSv3/XPG6 specify.
1496 The behavior of the matcher in bash-2.05 and later versions depends on the
1497 current LC_COLLATE setting. Setting this variable to `C' or `POSIX' will
1498 result in the traditional behavior ([A-Z] matches all uppercase ASCII
1499 characters). Many other locales, including the en_US locale (the default
1500 on many US versions of Linux) collate the upper and lower case letters like
1505 which means that [A-Z] matches every letter except `z'. Others collate like
1509 which means that [A-Z] matches every letter except `a'.
1511 The portable way to specify upper case letters is [:upper:] instead of
1512 A-Z; lower case may be specified as [:lower:] instead of a-z.
1514 Look at the manual pages for setlocale(3), strcoll(3), and, if it is
1515 present, locale(1). If you have locale(1), you can use it to find
1516 your current locale information even if you do not have any of the
1523 into /etc/profile and inspect any shell scripts run from cron for
1524 constructs like [A-Z]. This will prevent things like
1528 from removing every file in the current directory except those beginning
1529 with `z' and still allow individual users to change the collation order.
1530 Users may put the above command into their own profiles as well, of course.
1532 E10) Why does `cd //' leave $PWD as `//'?
1534 POSIX.2, in its description of `cd', says that *three* or more leading
1535 slashes may be replaced with a single slash when canonicalizing the
1536 current working directory.
1538 This is, I presume, for historical compatibility. Certain versions of
1539 Unix, and early network file systems, used paths of the form
1540 //hostname/path to access `path' on server `hostname'.
1542 E11) If I resize my xterm while another program is running, why doesn't bash
1545 This is another issue that deals with job control.
1547 The kernel maintains a notion of a current terminal process group. Members
1548 of this process group (processes whose process group ID is equal to the
1549 current terminal process group ID) receive terminal-generated signals like
1550 SIGWINCH. (For more details, see the JOB CONTROL section of the bash
1553 If a terminal is resized, the kernel sends SIGWINCH to each member of
1554 the terminal's current process group (the `foreground' process group).
1556 When bash is running with job control enabled, each pipeline (which may be
1557 a single command) is run in its own process group, different from bash's
1558 process group. This foreground process group receives the SIGWINCH; bash
1559 does not. Bash has no way of knowing that the terminal has been resized.
1561 There is a `checkwinsize' option, settable with the `shopt' builtin, that
1562 will cause bash to check the window size and adjust its idea of the
1563 terminal's dimensions each time a process stops or exits and returns control
1564 of the terminal to bash. Enable it with `shopt -s checkwinsize'.
1566 E12) Why don't negative offsets in substring expansion work like I expect?
1568 When substring expansion of the form ${param:offset[:length} is used,
1569 an `offset' that evaluates to a number less than zero counts back from
1570 the end of the expanded value of $param.
1572 When a negative `offset' begins with a minus sign, however, unexpected things
1573 can happen. Consider
1578 intending to print the last four characters of $a. The problem is that
1579 ${param:-word} already has a well-defined meaning: expand to word if the
1580 expanded value of param is unset or null, and $param otherwise.
1582 To use negative offsets that begin with a minus sign, separate the
1583 minus sign and the colon with a space.
1585 E13) Why does filename completion misbehave if a colon appears in the filename?
1587 Filename completion (and word completion in general) may appear to behave
1588 improperly if there is a colon in the word to be completed.
1590 The colon is special to readline's word completion code: it is one of the
1591 characters that breaks words for the completer. Readline uses these characters
1592 in sort of the same way that bash uses $IFS: they break or separate the words
1593 the completion code hands to the application-specific or default word
1594 completion functions. The original intent was to make it easy to edit
1595 colon-separated lists (such as $PATH in bash) in various applications using
1598 This is complicated by the fact that some versions of the popular
1599 `bash-completion' programmable completion package have problems with the
1600 default completion behavior in the presence of colons.
1602 The current set of completion word break characters is available in bash as
1603 the value of the COMP_WORDBREAKS variable. Removing `:' from that value is
1604 enough to make the colon not special to completion:
1606 COMP_WORDBREAKS=${COMP_WORDBREAKS//:}
1608 You can also quote the colon with a backslash to achieve the same result
1611 E14) Why does quoting the pattern argument to the regular expression matching
1612 conditional operator (=~) cause regexp matching to stop working?
1614 In versions of bash prior to bash-3.2, the effect of quoting the regular
1615 expression argument to the [[ command's =~ operator was not specified.
1616 The practical effect was that double-quoting the pattern argument required
1617 backslashes to quote special pattern characters, which interfered with the
1618 backslash processing performed by double-quoted word expansion and was
1619 inconsistent with how the == shell pattern matching operator treated
1622 In bash-3.2, the shell was changed to internally quote characters in single-
1623 and double-quoted string arguments to the =~ operator, which suppresses the
1624 special meaning of the characters special to regular expression processing
1625 (`.', `[', `\', `(', `), `*', `+', `?', `{', `|', `^', and `$') and forces
1626 them to be matched literally. This is consistent with how the `==' pattern
1627 matching operator treats quoted portions of its pattern argument.
1629 Since the treatment of quoted string arguments was changed, several issues
1630 have arisen, chief among them the problem of white space in pattern arguments
1631 and the differing treatment of quoted strings between bash-3.1 and bash-3.2.
1632 Both problems may be solved by using a shell variable to hold the pattern.
1633 Since word splitting is not performed when expanding shell variables in all
1634 operands of the [[ command, this allows users to quote patterns as they wish
1635 when assigning the variable, then expand the values to a single string that
1636 may contain whitespace. The first problem may be solved by using backslashes
1637 or any other quoting mechanism to escape the white space in the patterns.
1639 Bash-4.0 introduces the concept of a `compatibility level', controlled by
1640 several options to the `shopt' builtin. If the `compat31' option is enabled,
1641 bash reverts to the bash-3.1 behavior with respect to quoting the rhs of
1644 Section F: Things to watch out for on certain Unix versions
1646 F1) Why can't I use command line editing in my `cmdtool'?
1648 The problem is `cmdtool' and bash fighting over the input. When
1649 scrolling is enabled in a cmdtool window, cmdtool puts the tty in
1650 `raw mode' to permit command-line editing using the mouse for
1651 applications that cannot do it themselves. As a result, bash and
1652 cmdtool each try to read keyboard input immediately, with neither
1653 getting enough of it to be useful.
1655 This mode also causes cmdtool to not implement many of the
1656 terminal functions and control sequences appearing in the
1657 `sun-cmd' termcap entry. For a more complete explanation, see
1658 that file examples/suncmd.termcap in the bash distribution.
1660 `xterm' is a better choice, and gets along with bash much more
1663 If you must use cmdtool, you can use the termcap description in
1664 examples/suncmd.termcap. Set the TERMCAP variable to the terminal
1665 description contained in that file, i.e.
1667 TERMCAP='Mu|sun-cmd:am:bs:km:pt:li#34:co#80:cl=^L:ce=\E[K:cd=\E[J:rs=\E[s:'
1669 Then export TERMCAP and start a new cmdtool window from that shell.
1670 The bash command-line editing should behave better in the new
1671 cmdtool. If this works, you can put the assignment to TERMCAP
1672 in your bashrc file.
1674 F2) I built bash on Solaris 2. Why do globbing expansions and filename
1675 completion chop off the first few characters of each filename?
1677 This is the consequence of building bash on SunOS 5 and linking
1678 with the libraries in /usr/ucblib, but using the definitions
1679 and structures from files in /usr/include.
1681 The actual conflict is between the dirent structure in
1682 /usr/include/dirent.h and the struct returned by the version of
1683 `readdir' in libucb.a (a 4.3-BSD style `struct direct').
1685 Make sure you've got /usr/ccs/bin ahead of /usr/ucb in your $PATH
1686 when configuring and building bash. This will ensure that you
1687 use /usr/ccs/bin/cc or acc instead of /usr/ucb/cc and that you
1688 link with libc before libucb.
1690 If you have installed the Sun C compiler, you may also need to
1691 put /usr/ccs/bin and /opt/SUNWspro/bin into your $PATH before
1694 F3) Why does bash dump core after I interrupt username completion or
1695 `~user' tilde expansion on a machine running NIS?
1697 This is a famous and long-standing bug in the SunOS YP (sorry, NIS)
1698 client library, which is part of libc.
1700 The YP library code keeps static state -- a pointer into the data
1701 returned from the server. When YP initializes itself (setpwent),
1702 it looks at this pointer and calls free on it if it's non-null.
1705 If one of the YP functions is interrupted during getpwent (the
1706 exact function is interpretwithsave()), and returns NULL, the
1707 pointer is freed without being reset to NULL, and the function
1708 returns. The next time getpwent is called, it sees that this
1709 pointer is non-null, calls free, and the bash free() blows up
1710 because it's being asked to free freed memory.
1712 The traditional Unix mallocs allow memory to be freed multiple
1713 times; that's probably why this has never been fixed. You can
1714 run configure with the `--without-gnu-malloc' option to use
1715 the C library malloc and avoid the problem.
1717 F4) I'm running SVR4.2. Why is the line erased every time I type `@'?
1719 The `@' character is the default `line kill' character in most
1720 versions of System V, including SVR4.2. You can change this
1721 character to whatever you want using `stty'. For example, to
1722 change the line kill character to control-u, type
1726 where the `^' and `U' can be two separate characters.
1728 F5) Why does bash report syntax errors when my C News scripts use a
1729 redirection before a subshell command?
1731 The actual command in question is something like
1735 According to the grammar given in the POSIX.2 standard, this construct
1736 is, in fact, a syntax error. Redirections may only precede `simple
1737 commands'. A subshell construct such as the above is one of the shell's
1738 `compound commands'. A redirection may only follow a compound command.
1740 This affects the mechanical transformation of commands that use `cat'
1741 to pipe a file into a command (a favorite Useless-Use-Of-Cat topic on
1742 comp.unix.shell). While most commands of the form
1746 can be converted to `< file command', shell control structures such as
1747 loops and subshells require `command < file'.
1749 The file CWRU/sh-redir-hack in the bash distribution is an
1750 (unofficial) patch to parse.y that will modify the grammar to
1751 support this construct. It will not apply with `patch'; you must
1752 modify parse.y by hand. Note that if you apply this, you must
1753 recompile with -DREDIRECTION_HACK. This introduces a large
1754 number of reduce/reduce conflicts into the shell grammar.
1756 F6) Why can't I use vi-mode editing on Red Hat Linux 6.1?
1758 The short answer is that Red Hat screwed up.
1760 The long answer is that they shipped an /etc/inputrc that only works
1761 for emacs mode editing, and then screwed all the vi users by setting
1762 INPUTRC to /etc/inputrc in /etc/profile.
1764 The short fix is to do one of the following: remove or rename
1765 /etc/inputrc, set INPUTRC=~/.inputrc in ~/.bashrc (or .bash_profile,
1766 but make sure you export it if you do), remove the assignment to
1767 INPUTRC from /etc/profile, add
1771 to the beginning of /etc/inputrc, or bracket the key bindings in
1772 /etc/inputrc with these lines
1778 F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on
1781 HP/UX's support for long double is imperfect at best.
1783 GCC will support it without problems, but the HP C library functions
1784 like strtold(3) and printf(3) don't actually work with long doubles.
1785 HP implemented a `long_double' type as a 4-element array of 32-bit
1786 ints, and that is what the library functions use. The ANSI C
1787 `long double' type is a 128-bit floating point scalar.
1789 The easiest fix, until HP fixes things up, is to edit the generated
1790 config.h and #undef the HAVE_LONG_DOUBLE line. After doing that,
1791 the compilation should complete successfully.
1793 Section G: How can I get bash to do certain common things?
1795 G1) How can I get bash to read and display eight-bit characters?
1797 This is a process requiring several steps.
1799 First, you must ensure that the `physical' data path is a full eight
1800 bits. For xterms, for example, the `vt100' resources `eightBitInput'
1801 and `eightBitOutput' should be set to `true'.
1803 Once you have set up an eight-bit path, you must tell the kernel and
1804 tty driver to leave the eighth bit of characters alone when processing
1805 keyboard input. Use `stty' to do this:
1807 stty cs8 -istrip -parenb
1809 For old BSD-style systems, you can use
1817 Finally, you need to tell readline that you will be inputting and
1818 displaying eight-bit characters. You use readline variables to do
1819 this. These variables can be set in your .inputrc or using the bash
1820 `bind' builtin. Here's an example using `bind':
1822 bash$ bind 'set convert-meta off'
1823 bash$ bind 'set meta-flag on'
1824 bash$ bind 'set output-meta on'
1826 The `set' commands between the single quotes may also be placed
1829 The script examples/scripts.noah/meta.bash encapsulates the bind
1830 commands in a shell function.
1832 G2) How do I write a function `x' to replace builtin command `x', but
1833 still invoke the command from within the function?
1835 This is why the `command' and `builtin' builtins exist. The
1836 `command' builtin executes the command supplied as its first
1837 argument, skipping over any function defined with that name. The
1838 `builtin' builtin executes the builtin command given as its first
1841 For example, to write a function to replace `cd' that writes the
1842 hostname and current directory to an xterm title bar, use
1843 something like the following:
1847 builtin cd "$@" && xtitle "$HOST: $PWD"
1850 This could also be written using `command' instead of `builtin';
1851 the version above is marginally more efficient.
1853 G3) How can I find the value of a shell variable whose name is the value
1854 of another shell variable?
1856 Versions of Bash newer than Bash-2.0 support this directly. You can use
1860 For example, the following sequence of commands will echo `z':
1866 For sh compatibility, use the `eval' builtin. The important
1867 thing to remember is that `eval' expands the arguments you give
1868 it again, so you need to quote the parts of the arguments that
1869 you want `eval' to act on.
1871 For example, this expression prints the value of the last positional
1874 eval echo \"\$\{$#\}\"
1876 The expansion of the quoted portions of this expression will be
1877 deferred until `eval' runs, while the `$#' will be expanded
1878 before `eval' is executed. In versions of bash later than bash-2.0,
1882 does the same thing.
1884 This is not the same thing as ksh93 `nameref' variables, though the syntax
1885 is similar. I may add namerefs in a future bash version.
1887 G4) How can I make the bash `time' reserved word print timing output that
1888 looks like the output from my system's /usr/bin/time?
1890 The bash command timing code looks for a variable `TIMEFORMAT' and
1891 uses its value as a format string to decide how to display the
1894 The value of TIMEFORMAT is a string with `%' escapes expanded in a
1895 fashion similar in spirit to printf(3). The manual page explains
1896 the meanings of the escape sequences in the format string.
1898 If TIMEFORMAT is not set, bash acts as if the following assignment had
1901 TIMEFORMAT=$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'
1903 The POSIX.2 default time format (used by `time -p command') is
1905 TIMEFORMAT=$'real %2R\nuser %2U\nsys %2S'
1907 The BSD /usr/bin/time format can be emulated with:
1909 TIMEFORMAT=$'\t%1R real\t%1U user\t%1S sys'
1911 The System V /usr/bin/time format can be emulated with:
1913 TIMEFORMAT=$'\nreal\t%1R\nuser\t%1U\nsys\t%1S'
1915 The ksh format can be emulated with:
1917 TIMEFORMAT=$'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS'
1919 G5) How do I get the current directory into my prompt?
1921 Bash provides a number of backslash-escape sequences which are expanded
1922 when the prompt string (PS1 or PS2) is displayed. The full list is in
1925 The \w expansion gives the full pathname of the current directory, with
1926 a tilde (`~') substituted for the current value of $HOME. The \W
1927 expansion gives the basename of the current directory. To put the full
1928 pathname of the current directory into the path without any tilde
1929 subsitution, use $PWD. Here are some examples:
1931 PS1='\w$ ' # current directory with tilde
1932 PS1='\W$ ' # basename of current directory
1933 PS1='$PWD$ ' # full pathname of current directory
1935 The single quotes are important in the final example to prevent $PWD from
1936 being expanded when the assignment to PS1 is performed.
1938 G6) How can I rename "*.foo" to "*.bar"?
1940 Use the pattern removal functionality described in D3. The following `for'
1941 loop will do the trick:
1947 G7) How can I translate a filename from uppercase to lowercase?
1949 The script examples/functions/lowercase, originally written by John DuBois,
1950 will do the trick. The converse is left as an exercise.
1952 G8) How can I write a filename expansion (globbing) pattern that will match
1953 all files in the current directory except "." and ".."?
1955 You must have set the `extglob' shell option using `shopt -s extglob' to use
1960 A solution that works without extended globbing is given in the Unix Shell
1961 FAQ, posted periodically to comp.unix.shell. It's a variant of
1965 (The ..?* catches files with names of three or more characters beginning
1968 Section H: Where do I go from here?
1970 H1) How do I report bugs in bash, and where should I look for fixes and
1973 Use the `bashbug' script to report bugs. It is built and
1974 installed at the same time as bash. It provides a standard
1975 template for reporting a problem and automatically includes
1976 information about your configuration and build environment.
1978 `bashbug' sends its reports to bug-bash@gnu.org, which
1979 is a large mailing list gatewayed to the usenet newsgroup gnu.bash.bug.
1981 Bug fixes, answers to questions, and announcements of new releases
1982 are all posted to gnu.bash.bug. Discussions concerning bash features
1983 and problems also take place there.
1985 To reach the bash maintainers directly, send mail to
1986 bash-maintainers@gnu.org.
1988 H2) What kind of bash documentation is there?
1990 First, look in the doc directory in the bash distribution. It should
1991 contain at least the following files:
1993 bash.1 an extensive, thorough Unix-style manual page
1994 builtins.1 a manual page covering just bash builtin commands
1995 bashref.texi a reference manual in GNU tex`info format
1996 bashref.info an info version of the reference manual
1998 article.ms text of an article written for The Linux Journal
1999 readline.3 a man page describing readline
2001 Postscript, HTML, and ASCII files created from the above source are
2002 available in the documentation distribution.
2004 There is additional documentation available for anonymous FTP from host
2005 ftp.cwru.edu in the `pub/bash' directory.
2007 Cameron Newham and Bill Rosenblatt have written a book on bash, published
2008 by O'Reilly and Associates. The book is based on Bill Rosenblatt's Korn
2009 Shell book. The title is ``Learning the Bash Shell'', and the ISBN number
2010 of the third edition, published in March, 2005, is 0-596-00965-8. Look for
2011 it in fine bookstores near you. This edition of the book has been updated
2014 The GNU Bash Reference Manual has been published as a printed book by
2015 Network Theory Ltd (Paperback, ISBN: 0-9541617-7-7, Nov. 2006). It covers
2016 bash-3.2 and is available from most online bookstores (see
2017 http://www.network-theory.co.uk/bash/manual/ for details). The publisher
2018 will donate $1 to the Free Software Foundation for each copy sold.
2020 Arnold Robbins and Nelson Beebe have written ``Classic Shell Scripting'',
2021 published by O'Reilly. The first edition, with ISBN number 0-596-00595-4,
2022 was published in May, 2005.
2024 Chris F. A. Johnson, a frequent contributor to comp.unix.shell and
2025 gnu.bash.bug, has written ``Shell Scripting Recipes: A Problem-Solution
2026 Approach,'' a new book on shell scripting, concentrating on features of
2027 the POSIX standard helpful to shell script writers. The first edition from
2028 Apress, with ISBN number 1-59059-471-1, was published in May, 2005.
2030 H3) What's coming in future versions?
2032 These are features I hope to include in a future version of bash.
2034 Rocky Bernstein's bash debugger (support is included with bash-4.0)
2036 H4) What's on the bash `wish list' for future versions?
2038 These are features that may or may not appear in a future version of bash.
2040 breaking some of the shell functionality into embeddable libraries
2041 a module system like zsh's, using dynamic loading like builtins
2042 a bash programmer's guide with a chapter on creating loadable builtins
2043 a better loadable interface to perl with access to the shell builtins and
2044 variables (contributions gratefully accepted)
2045 ksh93-like `nameref' variables
2046 ksh93-like `xx.yy' variables (including some of the .sh.* variables) and
2047 associated disipline functions
2048 Some of the new ksh93 pattern matching operators, like backreferencing
2050 H5) When will the next release appear?
2052 The next version will appear sometime in 2009. Never make predictions.
2054 This document is Copyright 1995-2009 by Chester Ramey.
2056 Permission is hereby granted, without written agreement and
2057 without license or royalty fees, to use, copy, and distribute
2058 this document for any purpose, provided that the above copyright
2059 notice appears in all copies of this document and that the
2060 contents of this document remain unaltered.