-This is m4.info, produced by makeinfo version 4.13 from m4.texinfo.
+This is m4.info, produced by makeinfo version 5.1 from m4.texi.
-This manual (28 February 2011) is for GNU M4 (version 1.4.16), a
+This manual (22 September 2013) is for GNU M4 (version 1.4.17), a
package containing an implementation of the m4 macro language.
- Copyright (C) 1989-1994, 2004-2011 Free Software Foundation, Inc.
+ Copyright (C) 1989-1994, 2004-2013 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
Foundation; with no Invariant Sections, no Front-Cover Texts, and
no Back-Cover Texts. A copy of the license is included in the
section entitled "GNU Free Documentation License."
-
INFO-DIR-SECTION Text creation and manipulation
START-INFO-DIR-ENTRY
* M4: (m4). A powerful macro processor.
GNU M4
******
-This manual (28 February 2011) is for GNU M4 (version 1.4.16), a
+This manual (22 September 2013) is for GNU M4 (version 1.4.17), a
package containing an implementation of the m4 macro language.
- Copyright (C) 1989-1994, 2004-2011 Free Software Foundation, Inc.
+ Copyright (C) 1989-1994, 2004-2013 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
no Back-Cover Texts. A copy of the license is included in the
section entitled "GNU Free Documentation License."
- GNU `m4' is an implementation of the traditional UNIX macro
+ GNU 'm4' is an implementation of the traditional UNIX macro
processor. It is mostly SVR4 compatible, although it has some
extensions (for example, handling more than 9 positional parameters to
-macros). `m4' also has builtin functions for including files, running
-shell commands, doing arithmetic, etc. Autoconf needs GNU `m4' for
-generating `configure' scripts, but not for running them.
+macros). 'm4' also has builtin functions for including files, running
+shell commands, doing arithmetic, etc. Autoconf needs GNU 'm4' for
+generating 'configure' scripts, but not for running them.
- GNU `m4' was originally written by Rene' Seindal, with subsequent
+ GNU 'm4' was originally written by Rene' Seindal, with subsequent
changes by Franc,ois Pinard and other volunteers on the Internet. All
-names and email addresses can be found in the files `m4-1.4.16/AUTHORS'
-and `m4-1.4.16/THANKS' from the GNU M4 distribution.
+names and email addresses can be found in the files 'm4-1.4.17/AUTHORS'
+and 'm4-1.4.17/THANKS' from the GNU M4 distribution.
- This is release 1.4.16. It is now considered stable: future
-releases in the 1.4.x series are only meant to fix bugs, increase speed,
-or improve documentation. However...
+ This is release 1.4.17. It is now considered stable: future releases
+in the 1.4.x series are only meant to fix bugs, increase speed, or
+improve documentation. However...
- An experimental feature, which would improve `m4' usefulness, allows
-for changing the syntax for what is a "word" in `m4'. You should use:
+ An experimental feature, which would improve 'm4' usefulness, allows
+for changing the syntax for what is a "word" in 'm4'. You should use:
./configure --enable-changeword
- if you want this feature compiled in. The current implementation
-slows down `m4' considerably and is hardly acceptable. In the future,
-`m4' 2.0 will come with a different set of new features that provide
-similar capabilities, but without the inefficiencies, so changeword
-will go away and _you should not count on it_.
+if you want this feature compiled in. The current implementation slows
+down 'm4' considerably and is hardly acceptable. In the future, 'm4'
+2.0 will come with a different set of new features that provide similar
+capabilities, but without the inefficiencies, so changeword will go away
+and _you should not count on it_.
* Menu:
* Preliminaries:: Introduction and preliminaries
-* Invoking m4:: Invoking `m4'
+* Invoking m4:: Invoking 'm4'
* Syntax:: Lexical and syntactic conventions
* Macros:: How to invoke macros
* Miscellaneous:: Miscellaneous builtin macros
* Frozen files:: Fast loading of frozen state
-* Compatibility:: Compatibility with other versions of `m4'
+* Compatibility:: Compatibility with other versions of 'm4'
* Answers:: Correct version of some examples
* Copying This Package:: How to make copies of the overall M4 package
* Copying This Manual:: How to make copies of this manual
* Indices:: Indices of concepts and macros
- --- The Detailed Node Listing ---
+ -- The Detailed Node Listing --
Introduction and preliminaries
-* Intro:: Introduction to `m4'
+* Intro:: Introduction to 'm4'
* History:: Historical references
* Bugs:: Problems and bugs
* Manual:: Using this manual
-Invoking `m4'
+Invoking 'm4'
* Operation modes:: Command line options for operation modes
* Preprocessor features:: Command line options for preprocessor features
Lexical and syntactic conventions
* Names:: Macro names
-* Quoted strings:: Quoting input to `m4'
-* Comments:: Comments in `m4' input
+* Quoted strings:: Quoting input to 'm4'
+* Comments:: Comments in 'm4' input
* Other tokens:: Other kinds of input tokens
-* Input processing:: How `m4' copies input to output
+* Input processing:: How 'm4' copies input to output
How to invoke macros
* Ifdef:: Testing if a macro is defined
* Ifelse:: If-else construct, or multibranch
-* Shift:: Recursion in `m4'
+* Shift:: Recursion in 'm4'
* Forloop:: Iteration by counting
* Foreach:: Iteration by list contents
* Stacks:: Working with definition stacks
* Errprint:: Printing error messages
* Location:: Printing current location
-* M4exit:: Exiting from `m4'
+* M4exit:: Exiting from 'm4'
Fast loading of frozen state
* Using frozen files:: Using frozen files
* Frozen file format:: Frozen file format
-Compatibility with other versions of `m4'
+Compatibility with other versions of 'm4'
* Extensions:: Extensions in GNU M4
* Incompatibilities:: Facilities in System V m4 not in GNU M4
Correct version of some examples
-* Improved exch:: Solution for `exch'
-* Improved forloop:: Solution for `forloop'
-* Improved foreach:: Solution for `foreach'
-* Improved copy:: Solution for `copy'
-* Improved m4wrap:: Solution for `m4wrap'
-* Improved cleardivert:: Solution for `cleardivert'
-* Improved capitalize:: Solution for `capitalize'
-* Improved fatal_error:: Solution for `fatal_error'
+* Improved exch:: Solution for 'exch'
+* Improved forloop:: Solution for 'forloop'
+* Improved foreach:: Solution for 'foreach'
+* Improved copy:: Solution for 'copy'
+* Improved m4wrap:: Solution for 'm4wrap'
+* Improved cleardivert:: Solution for 'cleardivert'
+* Improved capitalize:: Solution for 'capitalize'
+* Improved fatal_error:: Solution for 'fatal_error'
How to make copies of the overall M4 package
Indices of concepts and macros
-* Macro index:: Index for all `m4' macros
+* Macro index:: Index for all 'm4' macros
* Concept index:: Index for many concepts
+
\1f
File: m4.info, Node: Preliminaries, Next: Invoking m4, Prev: Top, Up: Top
1 Introduction and preliminaries
********************************
-This first chapter explains what GNU `m4' is, where `m4' comes from,
-how to read and use this documentation, how to call the `m4' program,
-and how to report bugs about it. It concludes by giving tips for
-reading the remainder of the manual.
+This first chapter explains what GNU 'm4' is, where 'm4' comes from, how
+to read and use this documentation, how to call the 'm4' program, and
+how to report bugs about it. It concludes by giving tips for reading
+the remainder of the manual.
- The following chapters then detail all the features of the `m4'
+ The following chapters then detail all the features of the 'm4'
language.
* Menu:
-* Intro:: Introduction to `m4'
+* Intro:: Introduction to 'm4'
* History:: Historical references
* Bugs:: Problems and bugs
* Manual:: Using this manual
\1f
File: m4.info, Node: Intro, Next: History, Up: Preliminaries
-1.1 Introduction to `m4'
+1.1 Introduction to 'm4'
========================
-`m4' is a macro processor, in the sense that it copies its input to the
+'m4' is a macro processor, in the sense that it copies its input to the
output, expanding macros as it goes. Macros are either builtin or
user-defined, and can take any number of arguments. Besides just doing
-macro expansion, `m4' has builtin functions for including named files,
+macro expansion, 'm4' has builtin functions for including named files,
running shell commands, doing integer arithmetic, manipulating text in
-various ways, performing recursion, etc.... `m4' can be used either as
-a front-end to a compiler, or as a macro processor in its own right.
+various ways, performing recursion, etc.... 'm4' can be used either as a
+front-end to a compiler, or as a macro processor in its own right.
- The `m4' macro processor is widely available on all UNIXes, and has
-been standardized by POSIX. Usually, only a small percentage of users
+ The 'm4' macro processor is widely available on all UNIXes, and has
+been standardized by POSIX. Usually, only a small percentage of users
are aware of its existence. However, those who find it often become
committed users. The popularity of GNU Autoconf, which requires GNU
-`m4' for _generating_ `configure' scripts, is an incentive for many to
-install it, while these people will not themselves program in `m4'.
-GNU `m4' is mostly compatible with the System V, Release 3 version,
-except for some minor differences. *Note Compatibility::, for more
-details.
+'m4' for _generating_ 'configure' scripts, is an incentive for many to
+install it, while these people will not themselves program in 'm4'. GNU
+'m4' is mostly compatible with the System V, Release 4 version, except
+for some minor differences. *Note Compatibility::, for more details.
- Some people find `m4' to be fairly addictive. They first use `m4'
+ Some people find 'm4' to be fairly addictive. They first use 'm4'
for simple problems, then take bigger and bigger challenges, learning
-how to write complex sets of `m4' macros along the way. Once really
-addicted, users pursue writing of sophisticated `m4' applications even
-to solve simple problems, devoting more time debugging their `m4'
-scripts than doing real work. Beware that `m4' may be dangerous for
-the health of compulsive programmers.
+how to write complex sets of 'm4' macros along the way. Once really
+addicted, users pursue writing of sophisticated 'm4' applications even
+to solve simple problems, devoting more time debugging their 'm4'
+scripts than doing real work. Beware that 'm4' may be dangerous for the
+health of compulsive programmers.
\1f
File: m4.info, Node: History, Next: Bugs, Prev: Intro, Up: Preliminaries
1.2 Historical references
=========================
-`GPM' was an important ancestor of `m4'. See C. Strachey: "A General
-Purpose Macro generator", Computer Journal 8,3 (1965), pp. 225 ff.
-`GPM' is also succinctly described into David Gries classic "Compiler
-Construction for Digital Computers".
-
- The classic B. Kernighan and P.J. Plauger: "Software Tools",
-Addison-Wesley, Inc. (1976) describes and implements a Unix
-macro-processor language, which inspired Dennis Ritchie to write `m3',
-a macro processor for the AP-3 minicomputer.
+Macro languages were invented early in the history of computing. In the
+1950s Alan Perlis suggested that the macro language be independent of
+the language being processed. Techniques such as conditional and
+recursive macros, and using macros to define other macros, were
+described by Doug McIlroy of Bell Labs in "Macro Instruction Extensions
+of Compiler Languages", _Communications of the ACM_ 3, 4 (1960), 214-20,
+<http://dx.doi.org/10.1145/367177.367223>.
+
+ An important precursor of 'm4' was GPM; see C. Strachey, "A general
+purpose macrogenerator", _Computer Journal_ 8, 3 (1965), 225-41,
+<http://dx.doi.org/10.1093/comjnl/8.3.225>. GPM is also succinctly
+described in David Gries's book _Compiler Construction for Digital
+Computers_, Wiley (1971). Strachey was a brilliant programmer: GPM fit
+into 250 machine instructions!
+
+ Inspired by GPM while visiting Strachey's Lab in 1968, McIlroy wrote
+a model preprocessor in that fit into a page of Snobol 3 code, and
+McIlroy and Robert Morris developed a series of further models at Bell
+Labs. Andrew D. Hall followed up with M6, a general purpose macro
+processor used to port the Fortran source code of the Altran computer
+algebra system; see Hall's "The M6 Macro Processor", Computing Science
+Technical Report #2, Bell Labs (1972),
+<http://cm.bell-labs.com/cm/cs/cstr/2.pdf>. M6's source code consisted
+of about 600 Fortran statements. Its name was the first of the 'm4'
+line.
+
+ The Brian Kernighan and P.J. Plauger book _Software Tools_,
+Addison-Wesley (1976), describes and implements a Unix macro-processor
+language, which inspired Dennis Ritchie to write 'm3', a macro processor
+for the AP-3 minicomputer.
Kernighan and Ritchie then joined forces to develop the original
-`m4', as described in "The M4 Macro Processor", Bell Laboratories
-(1977). It had only 21 builtin macros.
+'m4', described in "The M4 Macro Processor", Bell Laboratories (1977),
+<http://wolfram.schneider.org/bsd/7thEdManVol2/m4/m4.pdf>. It had only
+21 builtin macros.
- While `GPM' was more _pure_, `m4' is meant to deal with the true
+ While 'GPM' was more _pure_, 'm4' is meant to deal with the true
intricacies of real life: macros can be recognized without being
pre-announced, skipping whitespace or end-of-lines is easier, more
constructs are builtin instead of derived, etc.
- Originally, the Kernighan and Plauger macro-processor, and then
-`m3', formed the engine for the Rational FORTRAN preprocessor, that is,
-the `Ratfor' equivalent of `cpp'. Later, `m4' was used as a front-end
-for `Ratfor', `C' and `Cobol'.
+ Originally, the Kernighan and Plauger macro-processor, and then 'm3',
+formed the engine for the Rational FORTRAN preprocessor, that is, the
+'Ratfor' equivalent of 'cpp'. Later, 'm4' was used as a front-end for
+'Ratfor', 'C' and 'Cobol'.
- Rene' Seindal released his implementation of `m4', GNU `m4', in
-1990, with the aim of removing the artificial limitations in many of
-the traditional `m4' implementations, such as maximum line length,
-macro size, or number of macros.
+ Rene' Seindal released his implementation of 'm4', GNU 'm4', in 1990,
+with the aim of removing the artificial limitations in many of the
+traditional 'm4' implementations, such as maximum line length, macro
+size, or number of macros.
The late Professor A. Dain Samples described and implemented a
-further evolution in the form of `M5': "User's Guide to the M5 Macro
+further evolution in the form of 'M5': "User's Guide to the M5 Macro
Language: 2nd edition", Electronic Announcement on comp.compilers
newsgroup (1992).
- Franc,ois Pinard took over maintenance of GNU `m4' in 1992, until
-1994 when he released GNU `m4' 1.4, which was the stable release for 10
+ Franc,ois Pinard took over maintenance of GNU 'm4' in 1992, until
+1994 when he released GNU 'm4' 1.4, which was the stable release for 10
years. It was at this time that GNU Autoconf decided to require GNU
-`m4' as its underlying engine, since all other implementations of `m4'
+'m4' as its underlying engine, since all other implementations of 'm4'
had too many limitations.
More recently, in 2004, Paul Eggert released 1.4.1 and 1.4.2 which
addressed some long standing bugs in the venerable 1.4 release. Then in
-2005, Gary V. Vaughan collected together the many patches to GNU `m4'
-1.4 that were floating around the net and released 1.4.3 and 1.4.4.
-And in 2006, Eric Blake joined the team and prepared patches for the
-release of 1.4.5, 1.4.6, 1.4.7, and 1.4.8. More bug fixes were
-incorporated in 2007, with releases 1.4.9 and 1.4.10. Eric continued
-with some portability fixes for 1.4.11 and 1.4.12 in 2008, 1.4.13 in
-2009, 1.4.14 and 1.4.15 in 2010, and 1.4.16 in 2011.
-
- Meanwhile, development has continued on new features for `m4', such
+2005, Gary V. Vaughan collected together the many patches to GNU 'm4'
+1.4 that were floating around the net and released 1.4.3 and 1.4.4. And
+in 2006, Eric Blake joined the team and prepared patches for the release
+of 1.4.5, 1.4.6, 1.4.7, and 1.4.8. More bug fixes were incorporated in
+2007, with releases 1.4.9 and 1.4.10. Eric continued with some
+portability fixes for 1.4.11 and 1.4.12 in 2008, 1.4.13 in 2009, 1.4.14
+and 1.4.15 in 2010, and 1.4.16 in 2011.
+
+ Meanwhile, development has continued on new features for 'm4', such
as dynamic module loading and additional builtins. When complete, GNU
-`m4' 2.0 will start a new series of releases.
+'m4' 2.0 will start a new series of releases.
\1f
File: m4.info, Node: Bugs, Next: Manual, Prev: History, Up: Preliminaries
Before reporting a bug or trying to fix it yourself, try to isolate
it to the smallest possible input file that reproduces the problem.
-Then send us the input file and the exact results `m4' gave you. Also
+Then send us the input file and the exact results 'm4' gave you. Also
say what you expected to occur; this will help us decide whether the
problem was really in the documentation.
Once you've got a precise problem, send e-mail to <bug-m4@gnu.org>.
-Please include the version number of `m4' you are using. You can get
-this information with the command `m4 --version'. Also provide details
+Please include the version number of 'm4' you are using. You can get
+this information with the command 'm4 --version'. Also provide details
about the platform you are executing on.
Non-bug suggestions are always welcome as well. If you have
-questions about things that are unclear in the documentation or are
-just obscure features, please report them too.
+questions about things that are unclear in the documentation or are just
+obscure features, please report them too.
\1f
File: m4.info, Node: Manual, Prev: Bugs, Up: Preliminaries
1.4 Using this manual
=====================
-This manual contains a number of examples of `m4' input and output, and
+This manual contains a number of examples of 'm4' input and output, and
a simple notation is used to distinguish input, output and error
-messages from `m4'. Examples are set out from the normal text, and
+messages from 'm4'. Examples are set out from the normal text, and
shown in a fixed width font, like this
This is an example of an example!
- To distinguish input from output, all output from `m4' is prefixed
-by the string `=>', and all error messages by the string `error-->'.
-When showing how command line options affect matters, the command line
-is shown with a prompt `$ like this', otherwise, you can assume that a
-simple `m4' invocation will work. Thus:
+ To distinguish input from output, all output from 'm4' is prefixed by
+the string '=>', and all error messages by the string 'error->'. When
+showing how command line options affect matters, the command line is
+shown with a prompt '$ 'like this'', otherwise, you can assume that a
+simple 'm4' invocation will work. Thus:
$ command line to invoke m4
Example of input line
=>Output line from m4
- error-->and an error message
+ error->and an error message
- The sequence `^D' in an example indicates the end of the input file.
-The sequence `<NL>' refers to the newline character. The majority of
+ The sequence '^D' in an example indicates the end of the input file.
+The sequence '<NL>' refers to the newline character. The majority of
these examples are self-contained, and you can run them with similar
-results by invoking `m4 -d'. In fact, the testsuite that is bundled in
+results by invoking 'm4 -d'. In fact, the testsuite that is bundled in
the GNU M4 package consists of the examples in this document! Some of
the examples assume that your current directory is located where you
unpacked the installation, so if you plan on following along, you may
find it helpful to do this now:
- $ cd m4-1.4.16
+ $ cd m4-1.4.17
- As each of the predefined macros in `m4' is described, a prototype
+ As each of the predefined macros in 'm4' is described, a prototype
call of the macro will be shown, giving descriptive names to the
arguments, e.g.,
- -- Composite: example (STRING, [COUNT = `1'], [ARGUMENT]...)
- This is a sample prototype. There is not really a macro named
- `example', but this documents that if there were, it would be a
- Composite macro, rather than a Builtin. It requires at least one
- argument, STRING. Remember that in `m4', there must not be a
- space between the macro name and the opening parenthesis, unless
- it was intended to call the macro without any arguments. The
- brackets around COUNT and ARGUMENT show that these arguments are
- optional. If COUNT is omitted, the macro behaves as if count were
- `1', whereas if ARGUMENT is omitted, the macro behaves as if it
- were the empty string. A blank argument is not the same as an
- omitted argument. For example, `example(`a')', `example(`a',`1')',
- and `example(`a',`1',)' would behave identically with COUNT set to
- `1'; while `example(`a',)' and `example(`a',`')' would explicitly
- pass the empty string for COUNT. The ellipses (`...') show that
- the macro processes additional arguments after ARGUMENT, rather
- than ignoring them.
-
- All macro arguments in `m4' are strings, but some are given special
+ -- Composite: example (STRING, [COUNT = '1']
+ [ARGUMENT]This is a sample prototype. There is not really a macro
+ named 'example', but this documents that if there were, it would be
+ a Composite macro, rather than a Builtin. It requires at least one
+ argument, STRING. Remember that in 'm4', there must not be a space
+ between the macro name and the opening parenthesis, unless it was
+ intended to call the macro without any arguments. The brackets
+ around COUNT and ARGUMENT show that these arguments are optional.
+ If COUNT is omitted, the macro behaves as if count were '1',
+ whereas if ARGUMENT is omitted, the macro behaves as if it were the
+ empty string. A blank argument is not the same as an omitted
+ argument. For example, 'example(`a')', 'example(`a',`1')', and
+ 'example(`a',`1',)' would behave identically with COUNT set to '1';
+ while 'example(`a',)' and 'example(`a',`')' would explicitly pass
+ the empty string for COUNT. The ellipses ('...') show that the
+ macro processes additional arguments after ARGUMENT, rather than
+ ignoring them.
+
+ All macro arguments in 'm4' are strings, but some are given special
interpretation, e.g., as numbers, file names, regular expressions, etc.
The documentation for each macro will state how the parameters are
-interpreted, and what happens if the argument cannot be parsed
-according to the desired interpretation. Unless specified otherwise, a
-parameter specified to be a number is parsed as a decimal, even if the
-argument has leading zeros; and parsing the empty string as a number
-results in 0 rather than an error, although a warning will be issued.
+interpreted, and what happens if the argument cannot be parsed according
+to the desired interpretation. Unless specified otherwise, a parameter
+specified to be a number is parsed as a decimal, even if the argument
+has leading zeros; and parsing the empty string as a number results in 0
+rather than an error, although a warning will be issued.
This document consistently writes and uses "builtin", without a
-hyphen, as if it were an English word. This is how the `builtin'
-primitive is spelled within `m4'.
+hyphen, as if it were an English word. This is how the 'builtin'
+primitive is spelled within 'm4'.
\1f
File: m4.info, Node: Invoking m4, Next: Syntax, Prev: Preliminaries, Up: Top
-2 Invoking `m4'
+2 Invoking 'm4'
***************
-The format of the `m4' command is:
+The format of the 'm4' command is:
- `m4' [OPTION...] [FILE...]
+ m4 [OPTION...] [FILE...]
- All options begin with `-', or if long option names are used, with
-`--'. A long option name need not be written completely, any
-unambiguous prefix is sufficient. POSIX requires `m4' to recognize
-arguments intermixed with files, even when `POSIXLY_CORRECT' is set in
+ All options begin with '-', or if long option names are used, with
+'--'. A long option name need not be written completely, any
+unambiguous prefix is sufficient. POSIX requires 'm4' to recognize
+arguments intermixed with files, even when 'POSIXLY_CORRECT' is set in
the environment. Most options take effect at startup regardless of
-their position, but some are documented below as taking effect after
-any files that occurred earlier in the command line. The argument `--'
-is a marker to denote the end of options.
+their position, but some are documented below as taking effect after any
+files that occurred earlier in the command line. The argument '--' is a
+marker to denote the end of options.
With short options, options that do not take arguments may be
combined into a single command line argument with subsequent options,
options with mandatory arguments may be provided either as a single
command line argument or as two arguments, and options with optional
-arguments must be provided as a single argument. In other words, `m4
--QPDfoo -d a -df' is equivalent to `m4 -Q -P -D foo -d -df -- ./a',
+arguments must be provided as a single argument. In other words, 'm4
+-QPDfoo -d a -df' is equivalent to 'm4 -Q -P -D foo -d -df -- ./a',
although the latter form is considered canonical.
With long options, options with mandatory arguments may be provided
-with an equal sign (`=') in a single argument, or as two arguments, and
+with an equal sign ('=') in a single argument, or as two arguments, and
options with optional arguments must be provided as a single argument.
-In other words, `m4 --def foo --debug a' is equivalent to `m4
+In other words, 'm4 --def foo --debug a' is equivalent to 'm4
--define=foo --debug= -- ./a', although the latter form is considered
-canonical (not to mention more robust, in case a future version of `m4'
-introduces an option named `--default').
+canonical (not to mention more robust, in case a future version of 'm4'
+introduces an option named '--default').
- `m4' understands the following options, grouped by functionality.
+ 'm4' understands the following options, grouped by functionality.
* Menu:
2.1 Command line options for operation modes
============================================
-Several options control the overall operation of `m4':
+Several options control the overall operation of 'm4':
-`--help'
- Print a help summary on standard output, then immediately exit
- `m4' without reading any input files or performing any other
- actions.
+'--help'
+ Print a help summary on standard output, then immediately exit 'm4'
+ without reading any input files or performing any other actions.
-`--version'
+'--version'
Print the version number of the program on standard output, then
- immediately exit `m4' without reading any input files or
- performing any other actions.
+ immediately exit 'm4' without reading any input files or performing
+ any other actions.
-`-E'
-`--fatal-warnings'
+'-E'
+'--fatal-warnings'
Controls the effect of warnings. If unspecified, then execution
continues and exit status is unaffected when a warning is printed.
If specified exactly once, warnings become fatal; when one is
If specified multiple times, then execution halts with non-zero
status the first time a warning is issued. The introduction of
behavior levels is new to M4 1.4.9; for behavior consistent with
- earlier versions, you should specify `-E' twice.
+ earlier versions, you should specify '-E' twice.
-`-i'
-`--interactive'
-`-e'
- Makes this invocation of `m4' interactive. This means that all
+'-i'
+'--interactive'
+'-e'
+ Makes this invocation of 'm4' interactive. This means that all
output will be unbuffered, and interrupts will be ignored. The
- spelling `-e' exists for compatibility with other `m4'
+ spelling '-e' exists for compatibility with other 'm4'
implementations, and issues a warning because it may be withdrawn
in a future version of GNU M4.
-`-P'
-`--prefix-builtins'
+'-P'
+'--prefix-builtins'
Internally modify _all_ builtin macro names so they all start with
- the prefix `m4_'. For example, using this option, one should write
- `m4_define' instead of `define', and `m4___file__' instead of
- `__file__'. This option has no effect if `-R' is also specified.
+ the prefix 'm4_'. For example, using this option, one should write
+ 'm4_define' instead of 'define', and 'm4___file__' instead of
+ '__file__'. This option has no effect if '-R' is also specified.
-`-Q'
-`--quiet'
-`--silent'
+'-Q'
+'--quiet'
+'--silent'
Suppress warnings, such as missing or superfluous arguments in
macro calls, or treating the empty string as zero.
-`--warn-macro-sequence[=REGEXP]'
+'--warn-macro-sequence[=REGEXP]'
Issue a warning if the regular expression REGEXP has a non-empty
- match in any macro definition (either by `define' or `pushdef').
- Empty matches are ignored; therefore, supplying the empty string
- as REGEXP disables any warning. If the optional REGEXP is not
+ match in any macro definition (either by 'define' or 'pushdef').
+ Empty matches are ignored; therefore, supplying the empty string as
+ REGEXP disables any warning. If the optional REGEXP is not
supplied, then the default regular expression is
- `\$\({[^}]*}\|[0-9][0-9]+\)' (a literal `$' followed by multiple
+ '\$\({[^}]*}\|[0-9][0-9]+\)' (a literal '$' followed by multiple
digits or by an open brace), since these sequences will change
semantics in the default operation of GNU M4 2.0 (due to a change
- in how more than 9 arguments in a macro definition will be
- handled, *note Arguments::). Providing an alternate regular
- expression can provide a useful reverse lookup feature of finding
- where a macro is defined to have a given definition.
+ in how more than 9 arguments in a macro definition will be handled,
+ *note Arguments::). Providing an alternate regular expression can
+ provide a useful reverse lookup feature of finding where a macro is
+ defined to have a given definition.
-`-W REGEXP'
-`--word-regexp=REGEXP'
+'-W REGEXP'
+'--word-regexp=REGEXP'
Use REGEXP as an alternative syntax for macro names. This
- experimental option will not be present in all GNU `m4'
+ experimental option will not be present in all GNU 'm4'
implementations (*note Changeword::).
\1f
2.2 Command line options for preprocessor features
==================================================
-Several options allow `m4' to behave more like a preprocessor. Macro
+Several options allow 'm4' to behave more like a preprocessor. Macro
definitions and deletions can be made on the command line, the search
path can be altered, and the output file can track where the input came
from. These features occur with the following options:
-`-D NAME[=VALUE]'
-`--define=NAME[=VALUE]'
- This enters NAME into the symbol table. If `=VALUE' is missing,
+'-D NAME[=VALUE]'
+'--define=NAME[=VALUE]'
+ This enters NAME into the symbol table. If '=VALUE' is missing,
the value is taken to be the empty string. The VALUE can be any
string, and the macro can be defined to take arguments, just as if
it was defined from within the input. This option may be given
more than once; order with respect to file names is significant,
and redefining the same NAME loses the previous value.
-`-I DIRECTORY'
-`--include=DIRECTORY'
- Make `m4' search DIRECTORY for included files that are not found
- in the current working directory. *Note Search Path::, for more
+'-I DIRECTORY'
+'--include=DIRECTORY'
+ Make 'm4' search DIRECTORY for included files that are not found in
+ the current working directory. *Note Search Path::, for more
details. This option may be given more than once.
-`-s'
-`--synclines'
+'-s'
+'--synclines'
Generate synchronization lines, for use by the C preprocessor or
other similar tools. Order is significant with respect to file
- names. This option is useful, for example, when `m4' is used as a
+ names. This option is useful, for example, when 'm4' is used as a
front end to a compiler. Source file name and line number
- information is conveyed by directives of the form `#line LINENUM
+ information is conveyed by directives of the form '#line LINENUM
"FILE"', which are inserted as needed into the middle of the
- output. Such directives mean that the following line originated
- or was expanded from the contents of input file FILE at line
- LINENUM. The `"FILE"' part is often omitted when the file name
- did not change from the previous directive.
+ output. Such directives mean that the following line originated or
+ was expanded from the contents of input file FILE at line LINENUM.
+ The '"FILE"' part is often omitted when the file name did not
+ change from the previous directive.
Synchronization directives are always given on complete lines by
themselves. When a synchronization discrepancy occurs in the
middle of an output line, the associated synchronization directive
- is delayed until the next newline that does not occur in the
- middle of a quoted string or comment.
+ is delayed until the next newline that does not occur in the middle
+ of a quoted string or comment.
define(`twoline', `1
2')
=>#line 12
=>goodbye
-`-U NAME'
-`--undefine=NAME'
+'-U NAME'
+'--undefine=NAME'
This deletes any predefined meaning NAME might have. Obviously,
- only predefined macros can be deleted in this way. This option
- may be given more than once; undefining a NAME that does not have a
+ only predefined macros can be deleted in this way. This option may
+ be given more than once; undefining a NAME that does not have a
definition is silently ignored. Order is significant with respect
to file names.
2.3 Command line options for limits control
===========================================
-There are some limits within `m4' that can be tuned. For
-compatibility, `m4' also accepts some options that control limits in
-other implementations, but which are automatically unbounded (limited
-only by your hardware and operating system constraints) in GNU `m4'.
+There are some limits within 'm4' that can be tuned. For compatibility,
+'m4' also accepts some options that control limits in other
+implementations, but which are automatically unbounded (limited only by
+your hardware and operating system constraints) in GNU 'm4'.
-`-g'
-`--gnu'
+'-g'
+'--gnu'
Enable all the extensions in this implementation. In this release
of M4, this option is always on by default; it is currently only
- useful when overriding a prior use of `--traditional'. However,
+ useful when overriding a prior use of '--traditional'. However,
having GNU behavior as default makes it impossible to write a
- strictly POSIX-compliant client that avoids all incompatible GNU
- M4 extensions, since such a client would have to use the non-POSIX
+ strictly POSIX-compliant client that avoids all incompatible GNU M4
+ extensions, since such a client would have to use the non-POSIX
command-line option to force full POSIX behavior. Thus, a future
version of M4 will be changed to implicitly use the option
- `--traditional' if the environment variable `POSIXLY_CORRECT' is
+ '--traditional' if the environment variable 'POSIXLY_CORRECT' is
set. Projects that intentionally use GNU extensions should
- consider using `--gnu' to state their intentions, so that the
- project will not mysteriously break if the user upgrades to a
- newer M4 and has `POSIXLY_CORRECT' set in their environment.
+ consider using '--gnu' to state their intentions, so that the
+ project will not mysteriously break if the user upgrades to a newer
+ M4 and has 'POSIXLY_CORRECT' set in their environment.
-`-G'
-`--traditional'
+'-G'
+'--traditional'
Suppress all the extensions made in this implementation, compared
to the System V version. *Note Compatibility::, for a list of
these.
-`-H NUM'
-`--hashsize=NUM'
+'-H NUM'
+'--hashsize=NUM'
Make the internal hash table for symbol lookup be NUM entries big.
For better performance, the number should be prime, but this is not
checked. The default is 509 entries. It should not be necessary
to increase this value, unless you define an excessive number of
macros.
-`-L NUM'
-`--nesting-limit=NUM'
+'-L NUM'
+'--nesting-limit=NUM'
Artificially limit the nesting of macro calls to NUM levels,
stopping program execution if this limit is ever exceeded. When
not specified, nesting defaults to unlimited on platforms that can
zero means unlimited; but then heavily nested code could
potentially cause a stack overflow.
- The precise effect of this option is more correctly associated
- with textual nesting than dynamic recursion. It has been useful
- when some complex `m4' input was generated by mechanical means, and
- also in diagnosing recursive algorithms that do not scale well.
- Most users never need to change this option from its default.
-
- This option does _not_ have the ability to break endless
- rescanning loops, since these do not necessarily consume much
- memory or stack space. Through clever usage of rescanning loops,
- one can request complex, time-consuming computations from `m4'
- with useful results. Putting limitations in this area would break
- `m4' power. There are many pathological cases:
- `define(`a', `a')a' is only the simplest example (but *note
- Compatibility::). Expecting GNU `m4' to detect these would be a
- little like expecting a compiler system to detect and diagnose
- endless loops: it is a quite _hard_ problem in general, if not
- undecidable!
-
-`-B NUM'
-`-S NUM'
-`-T NUM'
- These options are present for compatibility with System V `m4', but
+ The precise effect of this option is more correctly associated with
+ textual nesting than dynamic recursion. It has been useful when
+ some complex 'm4' input was generated by mechanical means, and also
+ in diagnosing recursive algorithms that do not scale well. Most
+ users never need to change this option from its default.
+
+ This option does _not_ have the ability to break endless rescanning
+ loops, since these do not necessarily consume much memory or stack
+ space. Through clever usage of rescanning loops, one can request
+ complex, time-consuming computations from 'm4' with useful results.
+ Putting limitations in this area would break 'm4' power. There are
+ many pathological cases: 'define(`a', `a')a' is only the simplest
+ example (but *note Compatibility::). Expecting GNU 'm4' to detect
+ these would be a little like expecting a compiler system to detect
+ and diagnose endless loops: it is a quite _hard_ problem in
+ general, if not undecidable!
+
+'-B NUM'
+'-S NUM'
+'-T NUM'
+ These options are present for compatibility with System V 'm4', but
do nothing in this implementation. They may disappear in future
releases, and issue a warning to that effect.
-`-N NUM'
-`--diversions=NUM'
+'-N NUM'
+'--diversions=NUM'
These options are present only for compatibility with previous
- versions of GNU `m4', and were controlling the number of possible
+ versions of GNU 'm4', and were controlling the number of possible
diversions which could be used at the same time. They do nothing,
because there is no fixed limit anymore. They may disappear in
future releases, and issue a warning to that effect.
2.4 Command line options for frozen state
=========================================
-GNU `m4' comes with a feature of freezing internal state (*note Frozen
-files::). This can be used to speed up `m4' execution when reusing a
+GNU 'm4' comes with a feature of freezing internal state (*note Frozen
+files::). This can be used to speed up 'm4' execution when reusing a
common initialization script.
-`-F FILE'
-`--freeze-state=FILE'
+'-F FILE'
+'--freeze-state=FILE'
Once execution is finished, write out the frozen state on the
specified FILE. It is conventional, but not required, for FILE to
- end in `.m4f'.
+ end in '.m4f'.
-`-R FILE'
-`--reload-state=FILE'
+'-R FILE'
+'--reload-state=FILE'
Before execution starts, recover the internal state from the
- specified frozen FILE. The options `-D', `-U', and `-t' take
+ specified frozen FILE. The options '-D', '-U', and '-t' take
effect after state is reloaded, but before the input files are
read.
2.5 Command line options for debugging
======================================
-Finally, there are several options for aiding in debugging `m4' scripts.
+Finally, there are several options for aiding in debugging 'm4' scripts.
-`-d[FLAGS]'
-`--debug[=FLAGS]'
+'-d[FLAGS]'
+'--debug[=FLAGS]'
Set the debug-level according to the flags FLAGS. The debug-level
controls the format and amount of information presented by the
- debugging functions. *Note Debug Levels::, for more details on
- the format and meaning of FLAGS. If omitted, FLAGS defaults to
- `aeq'.
-
-`--debugfile[=FILE]'
-`-o FILE'
-`--error-output=FILE'
- Redirect `dumpdef' output, debug messages, and trace output to the
- named FILE. Warnings, error messages, and `errprint' output are
+ debugging functions. *Note Debug Levels::, for more details on the
+ format and meaning of FLAGS. If omitted, FLAGS defaults to 'aeq'.
+
+'--debugfile[=FILE]'
+'-o FILE'
+'--error-output=FILE'
+ Redirect 'dumpdef' output, debug messages, and trace output to the
+ named FILE. Warnings, error messages, and 'errprint' output are
still printed to standard error. If these options are not used, or
- if FILE is unspecified (only possible for `--debugfile'), debug
+ if FILE is unspecified (only possible for '--debugfile'), debug
output goes to standard error; if FILE is the empty string, debug
output is discarded. *Note Debug Output::, for more details. The
- option `--debugfile' may be given more than once, and order is
- significant with respect to file names. The spellings `-o' and
- `--error-output' are misleading and inconsistent with other GNU
+ option '--debugfile' may be given more than once, and order is
+ significant with respect to file names. The spellings '-o' and
+ '--error-output' are misleading and inconsistent with other GNU
tools; for now they are silently accepted as synonyms of
- `--debugfile' and only recognized once, but in a future version of
+ '--debugfile' and only recognized once, but in a future version of
M4, using them will cause a warning to be issued.
-`-l NUM'
-`--arglength=NUM'
+'-l NUM'
+'--arglength=NUM'
Restrict the size of the output generated by macro tracing to NUM
characters per trace line. If unspecified or zero, output is
unlimited. *Note Debug Levels::, for more details.
-`-t NAME'
-`--trace=NAME'
+'-t NAME'
+'--trace=NAME'
This enables tracing for the macro NAME, at any point where it is
- defined. NAME need not be defined when this option is given.
- This option may be given more than once, and order is significant
- with respect to file names. *Note Trace::, for more details.
+ defined. NAME need not be defined when this option is given. This
+ option may be given more than once, and order is significant with
+ respect to file names. *Note Trace::, for more details.
\1f
File: m4.info, Node: Command line files, Prev: Debugging options, Up: Invoking m4
==============================================
The remaining arguments on the command line are taken to be input file
-names. If no names are present, standard input is read. A file name
-of `-' is taken to mean standard input. It is conventional, but not
-required, for input files to end in `.m4'.
+names. If no names are present, standard input is read. A file name of
+'-' is taken to mean standard input. It is conventional, but not
+required, for input files to end in '.m4'.
The input files are read in the sequence given. Standard input can
-be read more than once, so the file name `-' may appear multiple times
+be read more than once, so the file name '-' may appear multiple times
on the command line; this makes a difference when input is from a
terminal or other special file type. It is an error if an input file
ends in the middle of argument collection, a comment, or a quoted
string.
- The options `--define' (`-D'), `--undefine' (`-U'), `--synclines'
-(`-s'), and `--trace' (`-t') only take effect after processing input
+ The options '--define' ('-D'), '--undefine' ('-U'), '--synclines'
+('-s'), and '--trace' ('-t') only take effect after processing input
from any file names that occur earlier on the command line. For
-example, assume the file `foo' contains:
+example, assume the file 'foo' contains:
$ cat foo
bar
- The text `bar' can then be redefined over multiple uses of `foo':
+ The text 'bar' can then be redefined over multiple uses of 'foo':
$ m4 -Dbar=hello foo -Dbar=world foo
=>hello
=>world
- If none of the input files invoked `m4exit' (*note M4exit::), the
-exit status of `m4' will be 0 for success, 1 for general failure (such
+ If none of the input files invoked 'm4exit' (*note M4exit::), the
+exit status of 'm4' will be 0 for success, 1 for general failure (such
as problems with reading an input file), and 63 for version mismatch
(*note Using frozen files::).
- If you need to read a file whose name starts with a `-', you can
-specify it as `./-file', or use `--' to mark the end of options.
+ If you need to read a file whose name starts with a '-', you can
+specify it as './-file', or use '--' to mark the end of options.
\1f
File: m4.info, Node: Syntax, Next: Macros, Prev: Invoking m4, Up: Top
3 Lexical and syntactic conventions
***********************************
-As `m4' reads its input, it separates it into "tokens". A token is
+As 'm4' reads its input, it separates it into "tokens". A token is
either a name, a quoted string, or any single character, that is not a
-part of either a name or a string. Input to `m4' can also contain
-comments. GNU `m4' does not yet understand multibyte locales; all
-operations are byte-oriented rather than character-oriented (although
-if your locale uses a single byte encoding, such as ISO-8859-1, you
-will not notice a difference). However, `m4' is eight-bit clean, so
-you can use non-ASCII characters in quoted strings (*note
-Changequote::), comments (*note Changecom::), and macro names (*note
-Indir::), with the exception of the NUL character (the zero byte
-`'\0'').
+part of either a name or a string. Input to 'm4' can also contain
+comments. GNU 'm4' does not yet understand multibyte locales; all
+operations are byte-oriented rather than character-oriented (although if
+your locale uses a single byte encoding, such as ISO-8859-1, you will
+not notice a difference). However, 'm4' is eight-bit clean, so you can
+use non-ASCII characters in quoted strings (*note Changequote::),
+comments (*note Changecom::), and macro names (*note Indir::), with the
+exception of the NUL character (the zero byte ''\0'').
* Menu:
* Names:: Macro names
-* Quoted strings:: Quoting input to `m4'
-* Comments:: Comments in `m4' input
+* Quoted strings:: Quoting input to 'm4'
+* Comments:: Comments in 'm4' input
* Other tokens:: Other kinds of input tokens
-* Input processing:: How `m4' copies input to output
+* Input processing:: How 'm4' copies input to output
\1f
File: m4.info, Node: Names, Next: Quoted strings, Up: Syntax
3.1 Macro names
===============
-A name is any sequence of letters, digits, and the character `_'
-(underscore), where the first character is not a digit. `m4' will use
+A name is any sequence of letters, digits, and the character '_'
+(underscore), where the first character is not a digit. 'm4' will use
the longest such sequence found in the input. If a name has a macro
definition, it will be subject to macro expansion (*note Macros::).
Names are case-sensitive.
- Examples of legal names are: `foo', `_tmp', and `name01'.
+ Examples of legal names are: 'foo', '_tmp', and 'name01'.
\1f
File: m4.info, Node: Quoted strings, Next: Comments, Prev: Names, Up: Syntax
-3.2 Quoting input to `m4'
+3.2 Quoting input to 'm4'
=========================
-A quoted string is a sequence of characters surrounded by quote
-strings, defaulting to ``' and `'', where the nested begin and end
-quotes within the string are balanced. The value of a string token is
-the text, with one level of quotes stripped off. Thus
+A quoted string is a sequence of characters surrounded by quote strings,
+defaulting to '`' and ''', where the nested begin and end quotes within
+the string are balanced. The value of a string token is the text, with
+one level of quotes stripped off. Thus
`'
=>
=>`quoted'
The quote characters can be changed at any time, using the builtin
-macro `changequote'. *Note Changequote::, for more information.
+macro 'changequote'. *Note Changequote::, for more information.
\1f
File: m4.info, Node: Comments, Next: Other tokens, Prev: Quoted strings, Up: Syntax
-3.3 Comments in `m4' input
+3.3 Comments in 'm4' input
==========================
-Comments in `m4' are normally delimited by the characters `#' and
-newline. All characters between the comment delimiters are ignored,
-but the entire comment (including the delimiters) is passed through to
-the output--comments are _not_ discarded by `m4'.
+Comments in 'm4' are normally delimited by the characters '#' and
+newline. All characters between the comment delimiters are ignored, but
+the entire comment (including the delimiters) is passed through to the
+output--comments are _not_ discarded by 'm4'.
- Comments cannot be nested, so the first newline after a `#' ends the
+ Comments cannot be nested, so the first newline after a '#' ends the
comment. The commenting effect of the begin-comment string can be
inhibited by quoting it.
=>quoting inhibits # comments
The comment delimiters can be changed to any string at any time,
-using the builtin macro `changecom'. *Note Changecom::, for more
+using the builtin macro 'changecom'. *Note Changecom::, for more
information.
\1f
nor a comment, is a token by itself. When not in the context of macro
expansion, all of these tokens are just copied to output. However,
during macro expansion, whitespace characters (space, tab, newline,
-formfeed, carriage return, vertical tab), parentheses (`(' and `)'),
-comma (`,'), and dollar (`$') have additional roles, explained later.
+formfeed, carriage return, vertical tab), parentheses ('(' and ')'),
+comma (','), and dollar ('$') have additional roles, explained later.
\1f
File: m4.info, Node: Input processing, Prev: Other tokens, Up: Syntax
-3.5 How `m4' copies input to output
+3.5 How 'm4' copies input to output
===================================
-As `m4' reads the input token by token, it will copy each token
-directly to the output immediately.
+As 'm4' reads the input token by token, it will copy each token directly
+to the output immediately.
The exception is when it finds a word with a macro definition. In
-that case `m4' will calculate the macro's expansion, possibly reading
+that case 'm4' will calculate the macro's expansion, possibly reading
more input to get the arguments. It then inserts the expansion in front
of the remaining input. In other words, the resulting text from a macro
call will be read and parsed into tokens again.
- `m4' expands a macro as soon as possible. If it finds a macro call
+ 'm4' expands a macro as soon as possible. If it finds a macro call
when collecting the arguments to another, it will expand the second call
first. This process continues until there are no more macro calls to
expand and all the input has been consumed.
- For a running example, examine how `m4' handles this input:
+ For a running example, examine how 'm4' handles this input:
format(`Result is %d', eval(`2**15'))
-First, `m4' sees that the token `format' is a macro name, so it
-collects the tokens `(', ``Result is %d'', `,', and ` ', before
-encountering another potential macro. Sure enough, `eval' is a macro
-name, so the nested argument collection picks up `(', ``2**15'', and
-`)', invoking the eval macro with the lone argument of `2**15'. The
-expansion of `eval(2**15)' is `32768', which is then rescanned as the
-five tokens `3', `2', `7', `6', and `8'; and combined with the next
-`)', the format macro now has all its arguments, as if the user had
-typed:
+First, 'm4' sees that the token 'format' is a macro name, so it collects
+the tokens '(', '`Result is %d'', ',', and ' ', before encountering
+another potential macro. Sure enough, 'eval' is a macro name, so the
+nested argument collection picks up '(', '`2**15'', and ')', invoking
+the eval macro with the lone argument of '2**15'. The expansion of
+'eval(2**15)' is '32768', which is then rescanned as the five tokens
+'3', '2', '7', '6', and '8'; and combined with the next ')', the format
+macro now has all its arguments, as if the user had typed:
format(`Result is %d', 32768)
-The format macro expands to `Result is 32768', and we have another
-round of scanning for the tokens `Result', ` ', `is', ` ', `3', `2',
-`7', `6', and `8'. None of these are macros, so the final output is
+The format macro expands to 'Result is 32768', and we have another round
+of scanning for the tokens 'Result', ' ', 'is', ' ', '3', '2', '7', '6',
+and '8'. None of these are macros, so the final output is
=>Result is 32768
Oops - the argument did not get capitalized. And although the manual
is not able to easily show it, both lines that appear empty actually
contain two trailing spaces. By stepping through the parse, it is easy
-to see what happened. First, `m4' sees the token `changequote', which
-it recognizes as a macro, followed by `(', `[', `,', `]', and `)' to
+to see what happened. First, 'm4' sees the token 'changequote', which
+it recognizes as a macro, followed by '(', '[', ',', ']', and ')' to
form the argument list. The macro expands to the empty string, but
changes the quoting characters to something more useful for generating
-shell code (unbalanced ``' and `'' appear all the time in shell scripts,
-but unbalanced `[]' tend to be rare). Also in the first line, `m4'
-sees the token `dnl', which it recognizes as a builtin macro that
-consumes the rest of the line, resulting in no output for that line.
-
- The second line starts a macro definition. `m4' sees the token
-`define', which it recognizes as a macro, followed by a `(',
-`[gl_STRING_MODULE_INDICATOR]', and `,'. Because an unquoted comma was
+shell code (unbalanced '`' and ''' appear all the time in shell scripts,
+but unbalanced '[]' tend to be rare). Also in the first line, 'm4' sees
+the token 'dnl', which it recognizes as a builtin macro that consumes
+the rest of the line, resulting in no output for that line.
+
+ The second line starts a macro definition. 'm4' sees the token
+'define', which it recognizes as a macro, followed by a '(',
+'[gl_STRING_MODULE_INDICATOR]', and ','. Because an unquoted comma was
encountered, the first argument is known to be the expansion of the
-single-quoted string token, or `gl_STRING_MODULE_INDICATOR'. Next,
-`m4' sees `<NL>', ` ', and ` ', but this whitespace is discarded as
-part of argument collection. Then comes a rather lengthy single-quoted
-string token, `[<NL> dnl comment<NL> GNULIB_]'. This is followed
-by the token `translit', which `m4' recognizes as a macro name, so a
-nested macro expansion has started.
-
- The arguments to the `translit' are found by the tokens `(', `[$1]',
-`,', `[a-z]', `,', `[A-Z]', and finally `)'. All three string
-arguments are expanded (or in other words, the quotes are stripped),
-and since neither `$' nor `1' need capitalization, the result of the
-macro is `$1'. This expansion is rescanned, resulting in the two
-literal characters `$' and `1'.
-
- Scanning of the outer macro resumes, and picks up with `[=1<NL> ]',
-and finally `)'. The collected pieces of expanded text are
+single-quoted string token, or 'gl_STRING_MODULE_INDICATOR'. Next, 'm4'
+sees '<NL>', ' ', and ' ', but this whitespace is discarded as part of
+argument collection. Then comes a rather lengthy single-quoted string
+token, '[<NL> dnl comment<NL> GNULIB_]'. This is followed by the
+token 'translit', which 'm4' recognizes as a macro name, so a nested
+macro expansion has started.
+
+ The arguments to the 'translit' are found by the tokens '(', '[$1]',
+',', '[a-z]', ',', '[A-Z]', and finally ')'. All three string arguments
+are expanded (or in other words, the quotes are stripped), and since
+neither '$' nor '1' need capitalization, the result of the macro is
+'$1'. This expansion is rescanned, resulting in the two literal
+characters '$' and '1'.
+
+ Scanning of the outer macro resumes, and picks up with '[=1<NL> ]',
+and finally ')'. The collected pieces of expanded text are
concatenated, with the end result that the macro
-`gl_STRING_MODULE_INDICATOR' is now defined to be the sequence `<NL>
-dnl comment<NL> GNULIB_$1=1<NL> '. Once again, `dnl' is recognized
-and avoids a newline in the output.
-
- The final line is then parsed, beginning with ` ' and ` ' that are
-output literally. Then `gl_STRING_MODULE_INDICATOR' is recognized as a
-macro name, with an argument list of `(', `[strcase]', and `)'. Since
-the definition of the macro contains the sequence `$1', that sequence
-is replaced with the argument `strcase' prior to starting the rescan.
-The rescan sees `<NL>' and four spaces, which are output literally, then
-`dnl', which discards the text ` comment<NL>'. Next comes four more
-spaces, also output literally, and the token `GNULIB_strcase', which
+'gl_STRING_MODULE_INDICATOR' is now defined to be the sequence
+'<NL> dnl comment<NL> GNULIB_$1=1<NL> '. Once again, 'dnl' is
+recognized and avoids a newline in the output.
+
+ The final line is then parsed, beginning with ' ' and ' ' that are
+output literally. Then 'gl_STRING_MODULE_INDICATOR' is recognized as a
+macro name, with an argument list of '(', '[strcase]', and ')'. Since
+the definition of the macro contains the sequence '$1', that sequence is
+replaced with the argument 'strcase' prior to starting the rescan. The
+rescan sees '<NL>' and four spaces, which are output literally, then
+'dnl', which discards the text ' comment<NL>'. Next comes four more
+spaces, also output literally, and the token 'GNULIB_strcase', which
resulted from the earlier parameter substitution. Since that is not a
-macro name, it is output literally, followed by the literal tokens `=',
-`1', `<NL>', and two more spaces. Finally, the original `<NL>' seen
+macro name, it is output literally, followed by the literal tokens '=',
+'1', '<NL>', and two more spaces. Finally, the original '<NL>' seen
after the macro invocation is scanned and output literally.
Now for a corrected approach. This rearranges the use of newlines
and whitespace so that less whitespace is output (which, although
harmless to shell scripts, can be visually unappealing), and fixes the
quoting issues so that the capitalization occurs when the macro
-`gl_STRING_MODULE_INDICATOR' is invoked, rather then when it is
-defined. It also adds another layer of quoting to the first argument of
-`translit', to ensure that the output will be rescanned as a string
+'gl_STRING_MODULE_INDICATOR' is invoked, rather then when it is defined.
+It also adds another layer of quoting to the first argument of
+'translit', to ensure that the output will be rescanned as a string
rather than a potential uppercase macro name needing further expansion.
changequote([,])dnl
=> GNULIB_STRCASE=1
The parsing of the first line is unchanged. The second line sees the
-name of the macro to define, then sees the discarded `<NL>' and two
-spaces, as before. But this time, the next token is `[dnl comment<NL>
-GNULIB_[]translit([[$1]], [a-z], [A-Z])=1dnl<NL>]', which includes
-nested quotes, followed by `)' to end the macro definition and `dnl' to
-skip the newline. No early expansion of `translit' occurs, so the
-entire string becomes the definition of the macro.
+name of the macro to define, then sees the discarded '<NL>' and two
+spaces, as before. But this time, the next token is '[dnl
+comment<NL> GNULIB_[]translit([[$1]], [a-z], [A-Z])=1dnl<NL>]', which
+includes nested quotes, followed by ')' to end the macro definition and
+'dnl' to skip the newline. No early expansion of 'translit' occurs, so
+the entire string becomes the definition of the macro.
The final line is then parsed, beginning with two spaces that are
-output literally, and an invocation of `gl_STRING_MODULE_INDICATOR'
-with the argument `strcase'. Again, the `$1' in the macro definition
-is substituted prior to rescanning. Rescanning first encounters `dnl',
-and discards ` comment<NL>'. Then two spaces are output literally.
-Next comes the token `GNULIB_', but that is not a macro, so it is
-output literally. The token `[]' is an empty string, so it does not
-affect output. Then the token `translit' is encountered.
-
- This time, the arguments to `translit' are parsed as `(',
-`[[strcase]]', `,', ` ', `[a-z]', `,', ` ', `[A-Z]', and `)'. The two
+output literally, and an invocation of 'gl_STRING_MODULE_INDICATOR' with
+the argument 'strcase'. Again, the '$1' in the macro definition is
+substituted prior to rescanning. Rescanning first encounters 'dnl', and
+discards ' comment<NL>'. Then two spaces are output literally. Next
+comes the token 'GNULIB_', but that is not a macro, so it is output
+literally. The token '[]' is an empty string, so it does not affect
+output. Then the token 'translit' is encountered.
+
+ This time, the arguments to 'translit' are parsed as '(',
+'[[strcase]]', ',', ' ', '[a-z]', ',', ' ', '[A-Z]', and ')'. The two
spaces are discarded, and the translit results in the desired result
-`[STRCASE]'. This is rescanned, but since it is a string, the quotes
-are stripped and the only output is a literal `STRCASE'. Then the
-scanner sees `=' and `1', which are output literally, followed by `dnl'
+'[STRCASE]'. This is rescanned, but since it is a string, the quotes
+are stripped and the only output is a literal 'STRCASE'. Then the
+scanner sees '=' and '1', which are output literally, followed by 'dnl'
which discards the rest of the definition of
-`gl_STRING_MODULE_INDICATOR'. The newline at the end of output is the
-literal `<NL>' that appeared after the invocation of the macro.
+'gl_STRING_MODULE_INDICATOR'. The newline at the end of output is the
+literal '<NL>' that appeared after the invocation of the macro.
- The order in which `m4' expands the macros can be further explored
-using the trace facilities of GNU `m4' (*note Trace::).
+ The order in which 'm4' expands the macros can be further explored
+using the trace facilities of GNU 'm4' (*note Trace::).
---------- Footnotes ----------
(1) Derived from a patch in
-`http://lists.gnu.org/archive/html/bug-gnulib/2007-01/msg00389.html',
+<http://lists.gnu.org/archive/html/bug-gnulib/2007-01/msg00389.html>,
and a followup patch in
-`http://lists.gnu.org/archive/html/bug-gnulib/2007-02/msg00000.html'
+<http://lists.gnu.org/archive/html/bug-gnulib/2007-02/msg00000.html>
\1f
File: m4.info, Node: Macros, Next: Definitions, Prev: Syntax, Up: Top
spaces in between. If it does not, the macro is called with no
arguments at all.
- For a macro call to have no arguments, the parentheses _must_ be
-left out. The macro call
+ For a macro call to have no arguments, the parentheses _must_ be left
+out. The macro call
name()
4.2 Preventing macro invocation
===============================
-An innovation of the `m4' language, compared to some of its
-predecessors (like Strachey's `GPM', for example), is the ability to
-recognize macro calls without resorting to any special, prefixed
-invocation character. While generally useful, this feature might
-sometimes be the source of spurious, unwanted macro calls. So, GNU
-`m4' offers several mechanisms or techniques for inhibiting the
-recognition of names as macro calls.
+An innovation of the 'm4' language, compared to some of its predecessors
+(like Strachey's 'GPM', for example), is the ability to recognize macro
+calls without resorting to any special, prefixed invocation character.
+While generally useful, this feature might sometimes be the source of
+spurious, unwanted macro calls. So, GNU 'm4' offers several mechanisms
+or techniques for inhibiting the recognition of names as macro calls.
First of all, many builtin macros cannot meaningfully be called
without arguments. As a GNU extension, for any of these macros,
whenever an opening parenthesis does not immediately follow their name,
the builtin macro call is not triggered. This solves the most usual
-cases, like for `include' or `eval'. Later in this document, the
+cases, like for 'include' or 'eval'. Later in this document, the
sentence "This macro is recognized only with parameters" refers to this
specific provision of GNU M4, also known as a blind builtin macro. For
the builtins defined by POSIX that bear this disclaimer, POSIX
eval(`1')
=>1
- There is also a command line option (`--prefix-builtins', or `-P',
+ There is also a command line option ('--prefix-builtins', or '-P',
*note Invoking m4: Operation modes.) that renames all builtin macros
-with a prefix of `m4_' at startup. The option has no effect whatsoever
-on user defined macros. For example, with this option, one has to
-write `m4_dnl' and even `m4_m4exit'. It also has no effect on whether
-a macro requires parameters.
+with a prefix of 'm4_' at startup. The option has no effect whatsoever
+on user defined macros. For example, with this option, one has to write
+'m4_dnl' and even 'm4_m4exit'. It also has no effect on whether a macro
+requires parameters.
$ m4 -P
eval
=>1
Another alternative is to redefine problematic macros to a name less
-likely to cause conflicts, *Note Definitions::.
+likely to cause conflicts, using *note Definitions::.
- If your version of GNU `m4' has the `changeword' feature compiled
-in, it offers far more flexibility in specifying the syntax of macro
-names, both builtin or user-defined. *Note Changeword::, for more
-information on this experimental feature.
+ If your version of GNU 'm4' has the 'changeword' feature compiled in,
+it offers far more flexibility in specifying the syntax of macro names,
+both builtin or user-defined. *Note Changeword::, for more information
+on this experimental feature.
Of course, the simplest way to prevent a name from being interpreted
as a call to an existing macro is to quote it. The remainder of this
div`'ert
=>divert
-all yield the string `divert'. While in both:
+all yield the string 'divert'. While in both:
`'divert
=>
divert`'
=>
-the `divert' builtin macro will be called, which expands to the empty
+the 'divert' builtin macro will be called, which expands to the empty
string.
The output of macro evaluations is always rescanned. In the
-following example, the input `x`'y' yields the string `bCD', exactly as
-if `m4' has been given `substr(ab`'cde, `1', `3')' as input:
+following example, the input 'x`'y' yields the string 'bCD', exactly as
+if 'm4' has been given 'substr(ab`'cde, `1', `3')' as input:
define(`cde', `CDE')
=>
Unquoted strings on either side of a quoted string are subject to
being recognized as macro names. In the following example, quoting the
-empty string allows for the second `macro' to be recognized as such:
+empty string allows for the second 'macro' to be recognized as such:
define(`macro', `m')
=>
macro(`v')ert
=>
-the input will produce the string `divert'. When the quotes were
-removed, the `divert' builtin was called instead.
+the input will produce the string 'divert'. When the quotes were
+removed, the 'divert' builtin was called instead.
\1f
File: m4.info, Node: Macro Arguments, Next: Quoting Arguments, Prev: Inhibiting Invocation, Up: Macros
When a name is seen, and it has a macro definition, it will be expanded
as a macro.
- If the name is followed by an opening parenthesis, the arguments
-will be collected before the macro is called. If too few arguments are
+ If the name is followed by an opening parenthesis, the arguments will
+be collected before the macro is called. If too few arguments are
supplied, the missing arguments are taken to be the empty string.
However, some builtins are documented to behave differently for a
missing optional argument than for an explicit empty string. If there
=>unquoted trailing whitespace kept
=>
- Normally `m4' will issue warnings if a builtin macro is called with
+ Normally 'm4' will issue warnings if a builtin macro is called with
an inappropriate number of arguments, but it can be suppressed with the
-`--quiet' command line option (or `--silent', or `-Q', *note Invoking
+'--quiet' command line option (or '--silent', or '-Q', *note Invoking
m4: Operation modes.). For user defined macros, there is no check of
the number of arguments given.
$ m4
index(`abc')
- error-->m4:stdin:1: Warning: too few arguments to builtin `index'
+ error->m4:stdin:1: Warning: too few arguments to builtin `index'
=>0
index(`abc',)
=>0
index(`abc', `b', `ignored')
- error-->m4:stdin:3: Warning: excess arguments to builtin `index' ignored
+ error->m4:stdin:3: Warning: excess arguments to builtin `index' ignored
=>1
$ m4 -Q
Macros are expanded normally during argument collection, and whatever
commas, quotes and parentheses that might show up in the resulting
expanded text will serve to define the arguments as well. Thus, if FOO
-expands to `, b, c', the macro call
+expands to ', b, c', the macro call
bar(a foo, d)
-is a macro call with four arguments, which are `a ', `b', `c' and `d'.
+is a macro call with four arguments, which are 'a ', 'b', 'c' and 'd'.
To understand why the first argument contains whitespace, remember that
unquoted leading whitespace is never part of an argument, but trailing
whitespace always is.
It is possible for a macro's definition to change during argument
collection, in which case the expansion uses the definition that was in
-effect at the time the opening `(' was seen.
+effect at the time the opening '(' was seen.
define(`f', `1')
=>
=>hello world
define(
^D
- error-->m4:stdin:2: ERROR: end of file in argument list
+ error->m4:stdin:2: ERROR: end of file in argument list
\1f
File: m4.info, Node: Quoting Arguments, Next: Macro expansion, Prev: Macro Arguments, Up: Macros
==================================
Each argument has unquoted leading whitespace removed. Within each
-argument, all unquoted parentheses must match. For example, if FOO is
-a macro,
+argument, all unquoted parentheses must match. For example, if FOO is a
+macro,
foo(() (`(') `(')
-is a macro call, with one argument, whose value is `() (() ('. Commas
+is a macro call, with one argument, whose value is '() (() ('. Commas
separate arguments, except when they occur inside quotes, comments, or
unquoted parentheses. *Note Pseudo Arguments::, for examples.
It is common practice to quote all arguments to macros, unless you
are sure you want the arguments expanded. Thus, in the above example
-with the parentheses, the `right' way to do it is like this:
+with the parentheses, the 'right' way to do it is like this:
foo(`() (() (')
of parentheses introduces another layer of single quoting, except when
showing the consequences of quoting rules. This is done even when the
quoted string cannot be a macro, such as with integers when you have not
-changed the syntax via `changeword' (*note Changeword::).
+changed the syntax via 'changeword' (*note Changeword::).
- The quoting rule of thumb of one level of quoting per parentheses
-has a nice property: when a macro name appears inside parentheses, you
-can determine when it will be expanded. If it is not quoted, it will be
+ The quoting rule of thumb of one level of quoting per parentheses has
+a nice property: when a macro name appears inside parentheses, you can
+determine when it will be expanded. If it is not quoted, it will be
expanded prior to the outer macro, so that its expansion becomes the
argument. If it is single-quoted, it will be expanded after the outer
macro. And if it is double-quoted, it will be used as literal text
therefore result in more macros being called, if the calls are included,
completely or partially, in the first macro calls' expansion.
- Taking a very simple example, if FOO expands to `bar', and BAR
-expands to `Hello', the input
+ Taking a very simple example, if FOO expands to 'bar', and BAR
+expands to 'Hello', the input
$ m4 -Dbar=Hello -Dfoo=bar
foo
=>Hello
-will expand first to `bar', and when this is reread and expanded, into
-`Hello'.
+will expand first to 'bar', and when this is reread and expanded, into
+'Hello'.
\1f
File: m4.info, Node: Definitions, Next: Conditionals, Prev: Macros, Up: Top
====================
The normal way to define or redefine macros is to use the builtin
-`define':
+'define':
- -- Builtin: define (NAME, [EXPANSION])
- Defines NAME to expand to EXPANSION. If EXPANSION is not given,
- it is taken to be empty.
+ -- Builtin: define (NAME, [EXPANSION]
+ Defines NAME to expand to EXPANSION. If EXPANSION is not given, it
+ is taken to be empty.
- The expansion of `define' is void. The macro `define' is
+ The expansion of 'define' is void. The macro 'define' is
recognized only with parameters.
The following example defines the macro FOO to expand to the text
-`Hello World.'.
+'Hello World.'.
define(`foo', `Hello world.')
=>
The empty line in the output is there because the newline is not a
part of the macro definition, and it is consequently copied to the
-output. This can be avoided by use of the macro `dnl'. *Note Dnl::,
+output. This can be avoided by use of the macro 'dnl'. *Note Dnl::,
for details.
- The first argument to `define' should be quoted; otherwise, if the
+ The first argument to 'define' should be quoted; otherwise, if the
macro is already defined, you will be defining a different macro. This
example shows the problems with underquoting, since we did not want to
-redefine `one':
+redefine 'one':
define(foo, one)
=>
one
=>two
- GNU `m4' normally replaces only the _topmost_ definition of a macro
-if it has several definitions from `pushdef' (*note Pushdef::). Some
-other implementations of `m4' replace all definitions of a macro with
-`define'. *Note Incompatibilities::, for more details.
+ GNU 'm4' normally replaces only the _topmost_ definition of a macro
+if it has several definitions from 'pushdef' (*note Pushdef::). Some
+other implementations of 'm4' replace all definitions of a macro with
+'define'. *Note Incompatibilities::, for more details.
- As a GNU extension, the first argument to `define' does not have to
+ As a GNU extension, the first argument to 'define' does not have to
be a simple word. It can be any text string, even the empty string. A
macro with a non-standard name cannot be invoked in the normal way, as
the name is not recognized. It can only be referenced by the builtins
-`indir' (*note Indir::) and `defn' (*note Defn::).
+'indir' (*note Indir::) and 'defn' (*note Defn::).
Arrays and associative arrays can be simulated by using non-standard
macro names.
-- Composite: array (INDEX)
- -- Composite: array_set (INDEX, [VALUE])
- Provide access to entries within an array. `array' reads the entry
- at location INDEX, and `array_set' assigns VALUE to location INDEX.
+ -- Composite: array_set (INDEX, [VALUE]
+ Provide access to entries within an array. 'array' reads the entry
+ at location INDEX, and 'array_set' assigns VALUE to location INDEX.
define(`array', `defn(format(``array[%d]'', `$1'))')
=>
array(eval(`10 + 7'))
=>array element no. 17
- Change the `%d' to `%s' and it is an associative array.
+ Change the '%d' to '%s' and it is an associative array.
\1f
File: m4.info, Node: Arguments, Next: Pseudo Arguments, Prev: Define, Up: Definitions
5.2 Arguments to macros
=======================
-Macros can have arguments. The Nth argument is denoted by `$n' in the
+Macros can have arguments. The Nth argument is denoted by '$n' in the
expansion text, and is replaced by the Nth actual argument, when the
macro is expanded. Replacement of arguments happens before rescanning,
regardless of how many nesting levels of quoting appear in the
exch(`arg1', `arg2')
=>arg2, arg1
- This can be used, for example, if you like the arguments to `define'
+ This can be used, for example, if you like the arguments to 'define'
to be reversed.
define(`exch', `$2, $1')
=>expansion text
*Note Quoting Arguments::, for an explanation of the double quotes.
-(You should try and improve this example so that clients of `exch' do
+(You should try and improve this example so that clients of 'exch' do
not have to double quote; or *note Answers: Improved exch.).
- As a special case, the zeroth argument, `$0', is always the name of
+ As a special case, the zeroth argument, '$0', is always the name of
the macro being expanded.
define(`test', ``Macro name: $0'')
foo
=>This is macro foo.
-The `foo' in the expansion text is _not_ expanded, since it is a quoted
+The 'foo' in the expansion text is _not_ expanded, since it is a quoted
string, and not a name.
- GNU `m4' allows the number following the `$' to consist of one or
+ GNU 'm4' allows the number following the '$' to consist of one or
more digits, allowing macros to have any number of arguments. The
extension of accepting multiple digits is incompatible with POSIX, and
-is different than traditional implementations of `m4', which only
+is different than traditional implementations of 'm4', which only
recognize one digit. Therefore, future versions of GNU M4 will phase
-out this feature. To portably access beyond the ninth argument, you
-can use the `argn' macro documented later (*note Shift::).
+out this feature. To portably access beyond the ninth argument, you can
+use the 'argn' macro documented later (*note Shift::).
- POSIX also states that `$' followed immediately by `{' in a macro
+ POSIX also states that '$' followed immediately by '{' in a macro
definition is implementation-defined. This version of M4 passes the
-literal characters `${' through unchanged, but M4 2.0 will implement an
-optional feature similar to `sh', where `${11}' expands to the eleventh
-argument, to replace the current recognition of `$11'. Meanwhile, if
-you want to guarantee that you will get a literal `${' in output when
+literal characters '${' through unchanged, but M4 2.0 will implement an
+optional feature similar to 'sh', where '${11}' expands to the eleventh
+argument, to replace the current recognition of '$11'. Meanwhile, if
+you want to guarantee that you will get a literal '${' in output when
expanding a macro, even when you upgrade to M4 2.0, you can use nested
quoting to your advantage:
To help you detect places in your M4 input files that might change in
behavior due to the changed behavior of M4 2.0, you can use the
-`--warn-macro-sequence' command-line option (*note Invoking m4:
+'--warn-macro-sequence' command-line option (*note Invoking m4:
Operation modes.) with the default regular expression. This will add a
-warning any time a macro definition includes `$' followed by multiple
-digits, or by `{'. The warning is not enabled by default, because it
-triggers a number of warnings in Autoconf 2.61 (and Autoconf uses `-E'
+warning any time a macro definition includes '$' followed by multiple
+digits, or by '{'. The warning is not enabled by default, because it
+triggers a number of warnings in Autoconf 2.61 (and Autoconf uses '-E'
to treat warnings as errors), and because it will still be possible to
restore older behavior in M4 2.0.
$ m4 --warn-macro-sequence
define(`foo', `$001 ${1} $1')
- error-->m4:stdin:1: Warning: definition of `foo' contains sequence `$001'
- error-->m4:stdin:1: Warning: definition of `foo' contains sequence `${1}'
+ error->m4:stdin:1: Warning: definition of `foo' contains sequence `$001'
+ error->m4:stdin:1: Warning: definition of `foo' contains sequence `${1}'
=>
foo(`bar')
=>bar ${1} bar
There is a special notation for the number of actual arguments supplied,
and for all the actual arguments.
- The number of actual arguments in a macro call is denoted by `$#' in
+ The number of actual arguments in a macro call is denoted by '$#' in
the expansion text.
-- Composite: nargs (...)
nargs((unquoted parentheses, like this, group arguments))
=>1
- Remember that `#' defaults to the comment character; if you forget
+ Remember that '#' defaults to the comment character; if you forget
quotes to inhibit the comment behavior, your macro definition may not
end where you expected.
=>0)
=>oops
- The notation `$*' can be used in the expansion text to denote all
-the actual arguments, unquoted, with commas in between. For example
+ The notation '$*' can be used in the expansion text to denote all the
+actual arguments, unquoted, with commas in between. For example
define(`echo', `$*')
=>
echo(arg1, arg2, arg3 , arg4)
=>arg1,arg2,arg3 ,arg4
- Often each argument should be quoted, and the notation `$@' handles
-that. It is just like `$*', except that it quotes each argument. A
+ Often each argument should be quoted, and the notation '$@' handles
+that. It is just like '$*', except that it quotes each argument. A
simple example of that is:
define(`echo', `$@')
=>arg1,arg2,arg3 ,arg4
Where did the quotes go? Of course, they were eaten, when the
-expanded text were reread by `m4'. To show the difference, try
+expanded text were reread by 'm4'. To show the difference, try
define(`echo1', `$*')
=>
=>#foobar
=>bar'
- A `$' sign in the expansion text, that is not followed by anything
-`m4' understands, is simply copied to the macro expansion, as any other
+ A '$' sign in the expansion text, that is not followed by anything
+'m4' understands, is simply copied to the macro expansion, as any other
text is.
define(`foo', `$$$ hello $$$')
foo
=>$$$ hello $$$
- If you want a macro to expand to something like `$12', the judicious
-use of nested quoting can put a safe character between the `$' and the
+ If you want a macro to expand to something like '$12', the judicious
+use of nested quoting can put a safe character between the '$' and the
next character, relying on the rescanning to remove the nested quote.
-This will prevent `m4' from interpreting the `$' sign as a reference to
+This will prevent 'm4' from interpreting the '$' sign as a reference to
an argument.
define(`foo', `no nested quote: $1')
5.4 Deleting a macro
====================
-A macro definition can be removed with `undefine':
+A macro definition can be removed with 'undefine':
-- Builtin: undefine (NAME...)
For each argument, remove the macro NAME. The macro names must
necessarily be quoted, since they will be expanded otherwise.
- The expansion of `undefine' is void. The macro `undefine' is
+ The expansion of 'undefine' is void. The macro 'undefine' is
recognized only with parameters.
foo bar blah
=>foo bar blah
Undefining a macro inside that macro's expansion is safe; the macro
-still expands to the definition that was in effect at the `('.
+still expands to the definition that was in effect at the '('.
define(`f', ``$0':$1')
=>
=>f(bye)
It is not an error for NAME to have no macro definition. In that
-case, `undefine' does nothing.
+case, 'undefine' does nothing.
\1f
File: m4.info, Node: Defn, Next: Pushdef, Prev: Undefine, Up: Definitions
===================
It is possible to rename an already defined macro. To do this, you need
-the builtin `defn':
+the builtin 'defn':
-- Builtin: defn (NAME...)
- Expands to the _quoted definition_ of each NAME. If an argument
- is not a defined macro, the expansion for that argument is empty.
+ Expands to the _quoted definition_ of each NAME. If an argument is
+ not a defined macro, the expansion for that argument is empty.
If NAME is a user-defined macro, the quoted definition is simply
- the quoted expansion text. If, instead, there is only one NAME
- and it is a builtin, the expansion is a special token, which
- points to the builtin's internal definition. This token is only
- meaningful as the second argument to `define' (and `pushdef'), and
- is silently converted to an empty string in most other contexts.
- Combining a builtin with anything else is not supported; a warning
- is issued and the builtin is omitted from the final expansion.
+ the quoted expansion text. If, instead, there is only one NAME and
+ it is a builtin, the expansion is a special token, which points to
+ the builtin's internal definition. This token is only meaningful
+ as the second argument to 'define' (and 'pushdef'), and is silently
+ converted to an empty string in most other contexts. Combining a
+ builtin with anything else is not supported; a warning is issued
+ and the builtin is omitted from the final expansion.
- The macro `defn' is recognized only with parameters.
+ The macro 'defn' is recognized only with parameters.
- Its normal use is best understood through an example, which shows
-how to rename `undefine' to `zap':
+ Its normal use is best understood through an example, which shows how
+to rename 'undefine' to 'zap':
define(`zap', defn(`undefine'))
=>
undefine(`zap')
=>undefine(zap)
- In this way, `defn' can be used to copy macro definitions, and also
+ In this way, 'defn' can be used to copy macro definitions, and also
definitions of builtin macros. Even if the original macro is removed,
the other name can still be used to access the definition.
The fact that macro definitions can be transferred also explains why
-you should use `$0', rather than retyping a macro's name in its
+you should use '$0', rather than retyping a macro's name in its
definition:
define(`foo', `This is `$0'')
bar
=>This is bar
- Macros used as string variables should be referred through `defn',
-to avoid unwanted expansion of the text:
+ Macros used as string variables should be referred through 'defn', to
+avoid unwanted expansion of the text:
define(`string', `The macro dnl is very useful
')
=>The macro dnl is very useful
=>
- However, it is important to remember that `m4' rescanning is purely
+ However, it is important to remember that 'm4' rescanning is purely
textual. If an unbalanced end-quote string occurs in a macro
definition, the rescan will see that embedded quote as the termination
of the quoted string, and the remainder of the macro's definition will
echo(foo)
=>AA'
- On the other hand, it is possible to exploit the fact that `defn'
-can concatenate multiple macros prior to the rescanning phase, in order
-to join the definitions of macros that, in isolation, have unbalanced
+ On the other hand, it is possible to exploit the fact that 'defn' can
+concatenate multiple macros prior to the rescanning phase, in order to
+join the definitions of macros that, in isolation, have unbalanced
quotes. This is particularly useful when one has used several macros to
accumulate text that M4 should rescan as a whole. In the example below,
-note how the use of `defn' on `l' in isolation opens a string, which is
-not closed until the next line; but used on `l' and `r' together
-results in nested quoting.
+note how the use of 'defn' on 'l' in isolation opens a string, which is
+not closed until the next line; but used on 'l' and 'r' together results
+in nested quoting.
define(`l', `<[>')define(`r', `<]>')
=>
defn([l], [r])
=><[>][<]>
- Using `defn' to generate special tokens for builtin macros outside
-of expected contexts can sometimes trigger warnings. But most of the
-time, such tokens are silently converted to the empty string.
+ Using 'defn' to generate special tokens for builtin macros outside of
+expected contexts can sometimes trigger warnings. But most of the time,
+such tokens are silently converted to the empty string.
$ m4 -d
defn(`defn')
=>
define(defn(`divnum'), `cannot redefine a builtin token')
- error-->m4:stdin:2: Warning: define: invalid macro name ignored
+ error->m4:stdin:2: Warning: define: invalid macro name ignored
=>
divnum
=>0
len(defn(`divnum'))
=>0
- Also note that `defn' with multiple arguments can only join text
+ Also note that 'defn' with multiple arguments can only join text
macros, not builtins, although a future version of GNU M4 may lift this
restriction.
traceon(`defn', `define')
=>
defn(`a', `divnum', `a')
- error-->m4:stdin:3: Warning: cannot concatenate builtin `divnum'
- error-->m4trace: -1- defn(`a', `divnum', `a') -> ``A'`A''
+ error->m4:stdin:3: Warning: cannot concatenate builtin `divnum'
+ error->m4trace: -1- defn(`a', `divnum', `a') -> ``A'`A''
=>AA
define(`mydivnum', defn(`divnum', `divnum'))mydivnum
- error-->m4:stdin:4: Warning: cannot concatenate builtin `divnum'
- error-->m4:stdin:4: Warning: cannot concatenate builtin `divnum'
- error-->m4trace: -2- defn(`divnum', `divnum')
- error-->m4trace: -1- define(`mydivnum', `')
+ error->m4:stdin:4: Warning: cannot concatenate builtin `divnum'
+ error->m4:stdin:4: Warning: cannot concatenate builtin `divnum'
+ error->m4trace: -2- defn(`divnum', `divnum')
+ error->m4trace: -1- define(`mydivnum', `')
=>
traceoff(`defn', `define')
=>
It is possible to redefine a macro temporarily, reverting to the
previous definition at a later time. This is done with the builtins
-`pushdef' and `popdef':
+'pushdef' and 'popdef':
- -- Builtin: pushdef (NAME, [EXPANSION])
+ -- Builtin: pushdef (NAME, [EXPANSION]
-- Builtin: popdef (NAME...)
- Analogous to `define' and `undefine'.
+ Analogous to 'define' and 'undefine'.
These macros work in a stack-like fashion. A macro is temporarily
- redefined with `pushdef', which replaces an existing definition of
+ redefined with 'pushdef', which replaces an existing definition of
NAME, while saving the previous definition, before the new one is
- installed. If there is no previous definition, `pushdef' behaves
- exactly like `define'.
+ installed. If there is no previous definition, 'pushdef' behaves
+ exactly like 'define'.
If a macro has several definitions (of which only one is
- accessible), the topmost definition can be removed with `popdef'.
- If there is no previous definition, `popdef' behaves like
- `undefine'.
+ accessible), the topmost definition can be removed with 'popdef'.
+ If there is no previous definition, 'popdef' behaves like
+ 'undefine'.
- The expansion of both `pushdef' and `popdef' is void. The macros
- `pushdef' and `popdef' are recognized only with parameters.
+ The expansion of both 'pushdef' and 'popdef' is void. The macros
+ 'pushdef' and 'popdef' are recognized only with parameters.
define(`foo', `Expansion one.')
=>
foo
=>foo
- If a macro with several definitions is redefined with `define', the
+ If a macro with several definitions is redefined with 'define', the
topmost definition is _replaced_ with the new definition. If it is
-removed with `undefine', _all_ the definitions are removed, and not
-only the topmost one. However, POSIX allows other implementations that
-treat `define' as replacing an entire stack of definitions with a
-single new definition, so to be portable to other implementations, it
-may be worth explicitly using `popdef' and `pushdef' rather than
-relying on the GNU behavior of `define'.
+removed with 'undefine', _all_ the definitions are removed, and not only
+the topmost one. However, POSIX allows other implementations that treat
+'define' as replacing an entire stack of definitions with a single new
+definition, so to be portable to other implementations, it may be worth
+explicitly using 'popdef' and 'pushdef' rather than relying on the GNU
+behavior of 'define'.
define(`foo', `Expansion one.')
=>
foo
=>foo
- Local variables within macros are made with `pushdef' and `popdef'.
+ Local variables within macros are made with 'pushdef' and 'popdef'.
At the start of the macro a new definition is pushed, within the macro
it is manipulated and at the end it is popped, revealing the former
definition.
- It is possible to temporarily redefine a builtin with `pushdef' and
-`defn'.
+ It is possible to temporarily redefine a builtin with 'pushdef' and
+'defn'.
\1f
File: m4.info, Node: Indir, Next: Builtin, Prev: Pushdef, Up: Definitions
5.7 Indirect call of macros
===========================
-Any macro can be called indirectly with `indir':
+Any macro can be called indirectly with 'indir':
- -- Builtin: indir (NAME, [ARGS...])
+ -- Builtin: indir (NAME, [ARGS...]
Results in a call to the macro NAME, which is passed the rest of
the arguments ARGS. If NAME is not defined, an error message is
printed, and the expansion is void.
- The macro `indir' is recognized only with parameters.
+ The macro 'indir' is recognized only with parameters.
This can be used to call macros with computed or "invalid" names
-(`define' allows such names to be defined):
+('define' allows such names to be defined):
define(`$$internal$macro', `Internal macro (name `$0')')
=>
The point is, here, that larger macro packages can have private
macros defined, that will not be called by accident. They can _only_ be
-called through the builtin `indir'.
+called through the builtin 'indir'.
One other point to observe is that argument collection occurs before
-`indir' invokes NAME, so if argument collection changes the value of
+'indir' invokes NAME, so if argument collection changes the value of
NAME, that will be reflected in the final expansion. This is different
than the behavior when invoking macros directly, where the definition
that was in effect before argument collection is used.
indir(`f', define(`f', `3'))
=>3
indir(`f', undefine(`f'))
- error-->m4:stdin:4: undefined macro `f'
+ error->m4:stdin:4: undefined macro `f'
=>
- When handed the result of `defn' (*note Defn::) as one of its
-arguments, `indir' defers to the invoked NAME for whether a token
+ When handed the result of 'defn' (*note Defn::) as one of its
+arguments, 'indir' defers to the invoked NAME for whether a token
representing a builtin is recognized or flattened to the empty string.
$ m4 -d
indir(defn(`defn'), `divnum')
- error-->m4:stdin:1: Warning: indir: invalid macro name ignored
+ error->m4:stdin:1: Warning: indir: invalid macro name ignored
=>
indir(`define', defn(`defn'), `divnum')
- error-->m4:stdin:2: Warning: define: invalid macro name ignored
+ error->m4:stdin:2: Warning: define: invalid macro name ignored
=>
indir(`define', `foo', defn(`divnum'))
=>
foo
=>0
indir(`divert', defn(`foo'))
- error-->m4:stdin:5: empty string treated as 0 in builtin `divert'
+ error->m4:stdin:5: empty string treated as 0 in builtin `divert'
=>
\1f
5.8 Indirect call of builtins
=============================
-Builtin macros can be called indirectly with `builtin':
+Builtin macros can be called indirectly with 'builtin':
- -- Builtin: builtin (NAME, [ARGS...])
+ -- Builtin: builtin (NAME, [ARGS...]
Results in a call to the builtin NAME, which is passed the rest of
the arguments ARGS. If NAME does not name a builtin, an error
message is printed, and the expansion is void.
- The macro `builtin' is recognized only with parameters.
+ The macro 'builtin' is recognized only with parameters.
This can be used even if NAME has been given another definition that
-has covered the original, or been undefined so that no macro maps to
-the builtin.
+has covered the original, or been undefined so that no macro maps to the
+builtin.
pushdef(`define', `hidden')
=>
foo
=>foo
- The NAME argument only matches the original name of the builtin,
-even when the `--prefix-builtins' option (or `-P', *note Invoking m4:
-Operation modes.) is in effect. This is different from `indir', which
+ The NAME argument only matches the original name of the builtin, even
+when the '--prefix-builtins' option (or '-P', *note Invoking m4:
+Operation modes.) is in effect. This is different from 'indir', which
only tracks current macro names.
$ m4 -P
m4_builtin(`divnum')
=>0
m4_builtin(`m4_divnum')
- error-->m4:stdin:2: undefined builtin `m4_divnum'
+ error->m4:stdin:2: undefined builtin `m4_divnum'
=>
m4_indir(`divnum')
- error-->m4:stdin:3: undefined macro `divnum'
+ error->m4:stdin:3: undefined macro `divnum'
=>
m4_indir(`m4_divnum')
=>0
- Note that `indir' and `builtin' can be used to invoke builtins
+ Note that 'indir' and 'builtin' can be used to invoke builtins
without arguments, even when they normally require parameters to be
recognized; but it will provoke a warning, and result in a void
expansion.
builtin
=>builtin
builtin()
- error-->m4:stdin:2: undefined builtin `'
+ error->m4:stdin:2: undefined builtin `'
=>
builtin(`builtin')
- error-->m4:stdin:3: Warning: too few arguments to builtin `builtin'
+ error->m4:stdin:3: Warning: too few arguments to builtin `builtin'
=>
builtin(`builtin',)
- error-->m4:stdin:4: undefined builtin `'
+ error->m4:stdin:4: undefined builtin `'
=>
builtin(`builtin', ``'
')
- error-->m4:stdin:5: undefined builtin ``'
- error-->'
+ error->m4:stdin:5: undefined builtin ``'
+ error->'
=>
indir(`index')
- error-->m4:stdin:7: Warning: too few arguments to builtin `index'
+ error->m4:stdin:7: Warning: too few arguments to builtin `index'
=>
\1f
* Ifdef:: Testing if a macro is defined
* Ifelse:: If-else construct, or multibranch
-* Shift:: Recursion in `m4'
+* Shift:: Recursion in 'm4'
* Forloop:: Iteration by counting
* Foreach:: Iteration by list contents
* Stacks:: Working with definition stacks
6.1 Testing if a macro is defined
=================================
-There are two different builtin conditionals in `m4'. The first is
-`ifdef':
+There are two different builtin conditionals in 'm4'. The first is
+'ifdef':
- -- Builtin: ifdef (NAME, STRING-1, [STRING-2])
- If NAME is defined as a macro, `ifdef' expands to STRING-1,
+ -- Builtin: ifdef (NAME, STRING-1, [STRING-2]
+ If NAME is defined as a macro, 'ifdef' expands to STRING-1,
otherwise to STRING-2. If STRING-2 is omitted, it is taken to be
the empty string (according to the normal rules).
- The macro `ifdef' is recognized only with parameters.
+ The macro 'ifdef' is recognized only with parameters.
ifdef(`foo', ``foo' is defined', ``foo' is not defined')
=>foo is not defined
ifdef(`foo', ``foo' is defined', ``foo' is not defined')
=>foo is defined
ifdef(`no_such_macro', `yes', `no', `extra argument')
- error-->m4:stdin:4: Warning: excess arguments to builtin `ifdef' ignored
+ error->m4:stdin:4: Warning: excess arguments to builtin `ifdef' ignored
=>no
\1f
6.2 If-else construct, or multibranch
=====================================
-The other conditional, `ifelse', is much more powerful. It can be used
+The other conditional, 'ifelse', is much more powerful. It can be used
as a way to introduce a long comment, as an if-else construct, or as a
multibranch, depending on the number of arguments supplied:
-- Builtin: ifelse (COMMENT)
- -- Builtin: ifelse (STRING-1, STRING-2, EQUAL, [NOT-EQUAL])
+ -- Builtin: ifelse (STRING-1, STRING-2, EQUAL, [NOT-EQUAL]
-- Builtin: ifelse (STRING-1, STRING-2, EQUAL-1, STRING-3, STRING-4,
- EQUAL-2, ..., [NOT-EQUAL])
- Used with only one argument, the `ifelse' simply discards it and
+ EQUAL-2, ..., [NOT-EQUAL]
+ Used with only one argument, the 'ifelse' simply discards it and
produces no output.
- If called with three or four arguments, `ifelse' expands into
+ If called with three or four arguments, 'ifelse' expands into
EQUAL, if STRING-1 and STRING-2 are equal (character for
character), otherwise it expands to NOT-EQUAL. A final fifth
argument is ignored, after triggering a warning.
- If called with six or more arguments, and STRING-1 and STRING-2
- are equal, `ifelse' expands into EQUAL-1, otherwise the first
- three arguments are discarded and the processing starts again.
+ If called with six or more arguments, and STRING-1 and STRING-2 are
+ equal, 'ifelse' expands into EQUAL-1, otherwise the first three
+ arguments are discarded and the processing starts again.
- The macro `ifelse' is recognized only with parameters.
+ The macro 'ifelse' is recognized only with parameters.
- Using only one argument is a common `m4' idiom for introducing a
-block comment, as an alternative to repeatedly using `dnl'. This
-special usage is recognized by GNU `m4', so that in this case, the
+ Using only one argument is a common 'm4' idiom for introducing a
+block comment, as an alternative to repeatedly using 'dnl'. This
+special usage is recognized by GNU 'm4', so that in this case, the
warning about missing arguments is never triggered.
ifelse(`some comments')
=>
ifelse(`foo', `bar')
- error-->m4:stdin:2: Warning: too few arguments to builtin `ifelse'
+ error->m4:stdin:2: Warning: too few arguments to builtin `ifelse'
=>
Using three or four arguments provides decision points.
For an example of a way to make defining blind macros easier, see
*note Composition::.
- The macro `ifelse' can take more than four arguments. If given more
-than four arguments, `ifelse' works like a `case' or `switch' statement
+ The macro 'ifelse' can take more than four arguments. If given more
+than four arguments, 'ifelse' works like a 'case' or 'switch' statement
in traditional programming languages. If STRING-1 and STRING-2 are
-equal, `ifelse' expands into EQUAL-1, otherwise the procedure is
+equal, 'ifelse' expands into EQUAL-1, otherwise the procedure is
repeated with the first three arguments discarded. This calls for an
example:
ifelse(`foo', `bar', `third', `gnu', `gnats')
- error-->m4:stdin:1: Warning: excess arguments to builtin `ifelse' ignored
+ error->m4:stdin:1: Warning: excess arguments to builtin `ifelse' ignored
=>gnu
ifelse(`foo', `bar', `third', `gnu', `gnats', `sixth')
=>
ifelse(`foo', `bar', `third', `gnu', `gnats', `sixth', `seventh')
=>seventh
ifelse(`foo', `bar', `3', `gnu', `gnats', `6', `7', `8')
- error-->m4:stdin:4: Warning: excess arguments to builtin `ifelse' ignored
+ error->m4:stdin:4: Warning: excess arguments to builtin `ifelse' ignored
=>7
Naturally, the normal case will be slightly more advanced than these
-examples. A common use of `ifelse' is in macros implementing loops of
+examples. A common use of 'ifelse' is in macros implementing loops of
various kinds.
\1f
File: m4.info, Node: Shift, Next: Forloop, Prev: Ifelse, Up: Conditionals
-6.3 Recursion in `m4'
+6.3 Recursion in 'm4'
=====================
-There is no direct support for loops in `m4', but macros can be
+There is no direct support for loops in 'm4', but macros can be
recursive. There is no limit on the number of recursion levels, other
than those enforced by your hardware and operating system.
Loops can be programmed using recursion and the conditionals
described previously.
- There is a builtin macro, `shift', which can, among other things, be
+ There is a builtin macro, 'shift', which can, among other things, be
used for iterating through the actual arguments to a macro:
-- Builtin: shift (ARG1, ...)
Takes any number of arguments, and expands to all its arguments
except ARG1, separated by commas, with each argument quoted.
- The macro `shift' is recognized only with parameters.
+ The macro 'shift' is recognized only with parameters.
shift
=>shift
shift(`foo', `bar', `baz')
=>bar,baz
- An example of the use of `shift' is this macro:
+ An example of the use of 'shift' is this macro:
-- Composite: reverse (...)
Takes any number of arguments, and reverses their order.
reverse(`foo', `bar', `gnats', `and gnus')
=>and gnus, gnats, bar, foo
- While not a very interesting macro, it does show how simple loops
-can be made with `shift', `ifelse' and recursion. It also shows that
-`shift' is usually used with `$@'. Another example of this is an
+ While not a very interesting macro, it does show how simple loops can
+be made with 'shift', 'ifelse' and recursion. It also shows that
+'shift' is usually used with '$@'. Another example of this is an
implementation of a short-circuiting conditional operator.
- -- Composite: cond (TEST-1, STRING-1, EQUAL-1, [TEST-2], [STRING-2],
- [EQUAL-2], ..., [NOT-EQUAL])
- Similar to `ifelse', where an equal comparison between the first
+ -- Composite: cond (TEST-1, STRING-1, EQUAL-1, [TEST-2]
+ Similar to 'ifelse', where an equal comparison between the first
two strings results in the third, otherwise the first three
- arguments are discarded and the process repeats. The difference
- is that each TEST-<N> is expanded only when it is encountered.
- This means that every third argument to `cond' is normally given
- one more level of quoting than the corresponding argument to
- `ifelse'.
+ arguments are discarded and the process repeats. The difference is
+ that each TEST-<N> is expanded only when it is encountered. This
+ means that every third argument to 'cond' is normally given one
+ more level of quoting than the corresponding argument to 'ifelse'.
- Here is the implementation of `cond', along with a demonstration of
-how it can short-circuit the side effects in `side'. Notice how all
-the unquoted side effects happen regardless of how many comparisons are
-made with `ifelse', compared with only the relevant effects with `cond'.
+ Here is the implementation of 'cond', along with a demonstration of
+how it can short-circuit the side effects in 'side'. Notice how all the
+unquoted side effects happen regardless of how many comparisons are made
+with 'ifelse', compared with only the relevant effects with 'cond'.
define(`cond',
`ifelse(`$#', `1', `$1',
Another common task that requires iteration is joining a list of
arguments into a single string.
- -- Composite: join ([SEPARATOR], [ARGS...])
- -- Composite: joinall ([SEPARATOR], [ARGS...])
+ -- Composite: join ([SEPARATOR]
+ -- Composite: joinall ([SEPARATOR]
Generate a single-quoted string, consisting of each ARG separated
- by SEPARATOR. While `joinall' always outputs a SEPARATOR between
- arguments, `join' avoids the SEPARATOR for an empty ARG.
+ by SEPARATOR. While 'joinall' always outputs a SEPARATOR between
+ arguments, 'join' avoids the SEPARATOR for an empty ARG.
Here are some examples of its usage, based on the implementation
-`m4-1.4.16/examples/join.m4' distributed in this package:
+'m4-1.4.17/examples/join.m4' distributed in this package:
$ m4 -I examples
include(`join.m4')
=>`ifelse(`$#', `2', `', ``$1$3'$0(`$1', shift(shift($@)))')')
=>divert`'dnl
- First, notice that this implementation creates helper macros `_join'
-and `_joinall'. This division of labor makes it easier to output the
-correct number of SEPARATOR instances: `join' and `joinall' are
-responsible for the first argument, without a separator, while `_join'
-and `_joinall' are responsible for all remaining arguments, always
+ First, notice that this implementation creates helper macros '_join'
+and '_joinall'. This division of labor makes it easier to output the
+correct number of SEPARATOR instances: 'join' and 'joinall' are
+responsible for the first argument, without a separator, while '_join'
+and '_joinall' are responsible for all remaining arguments, always
outputting a separator when outputting an argument.
- Next, observe how `join' decides to iterate to itself, because the
-first ARG was empty, or to output the argument and swap over to
-`_join'. If the argument is non-empty, then the nested `ifelse'
-results in an unquoted `_', which is concatenated with the `$0' to form
-the next macro name to invoke. The `joinall' implementation is simpler
-since it does not have to suppress empty ARG; it always executes once
-then defers to `_joinall'.
+ Next, observe how 'join' decides to iterate to itself, because the
+first ARG was empty, or to output the argument and swap over to '_join'.
+If the argument is non-empty, then the nested 'ifelse' results in an
+unquoted '_', which is concatenated with the '$0' to form the next macro
+name to invoke. The 'joinall' implementation is simpler since it does
+not have to suppress empty ARG; it always executes once then defers to
+'_joinall'.
- Another important idiom is the idea that SEPARATOR is reused for
-each iteration. Each iteration has one less argument, but rather than
-discarding `$1' by iterating with `$0(shift($@))', the macro discards
-`$2' by using `$0(`$1', shift(shift($@)))'.
+ Another important idiom is the idea that SEPARATOR is reused for each
+iteration. Each iteration has one less argument, but rather than
+discarding '$1' by iterating with '$0(shift($@))', the macro discards
+'$2' by using '$0(`$1', shift(shift($@)))'.
Next, notice that it is possible to compare more than one condition
-in a single `ifelse' test. The test of `$#$2' against `2' allows
-`_join' to iterate for two separate reasons--either there are still
-more than two arguments, or there are exactly two arguments but the
-last argument is not empty.
+in a single 'ifelse' test. The test of '$#$2' against '2' allows
+'_join' to iterate for two separate reasons--either there are still more
+than two arguments, or there are exactly two arguments but the last
+argument is not empty.
Finally, notice that these macros require exactly two arguments to
terminate recursion, but that they still correctly result in empty
output when given no ARGS (i.e., zero or one macro argument). On the
-first pass when there are too few arguments, the `shift' results in no
+first pass when there are too few arguments, the 'shift' results in no
output, but leaves an empty string to serve as the required second
-argument for the second pass. Put another way, ``$1', shift($@)' is
-not the same as `$@', since only the former guarantees at least two
+argument for the second pass. Put another way, '`$1', shift($@)' is not
+the same as '$@', since only the former guarantees at least two
arguments.
Sometimes, a recursive algorithm requires adding quotes to each
-- Composite: quote (...)
-- Composite: dquote (...)
-- Composite: dquote_elt (...)
- Takes any number of arguments, and adds quoting. With `quote',
+ Takes any number of arguments, and adds quoting. With 'quote',
only one level of quoting is added, effectively removing whitespace
after commas and turning multiple arguments into a single string.
- With `dquote', two levels of quoting are added, one around each
- element, and one around the list. And with `dquote_elt', two
+ With 'dquote', two levels of quoting are added, one around each
+ element, and one around the list. And with 'dquote_elt', two
levels of quoting are added around each element.
An actual implementation of these three macros is distributed as
-`m4-1.4.16/examples/quote.m4' in this package. First, let's examine
+'m4-1.4.17/examples/quote.m4' in this package. First, let's examine
their usage:
$ m4 -I examples
dquote_elt(dquote(`1', `2'))
=>``1',`2''
- The last two lines show that when given two arguments, `dquote'
-results in one string, while `dquote_elt' results in two. Now, examine
-the implementation. Note that `quote' and `dquote_elt' make decisions
+ The last two lines show that when given two arguments, 'dquote'
+results in one string, while 'dquote_elt' results in two. Now, examine
+the implementation. Note that 'quote' and 'dquote_elt' make decisions
based on their number of arguments, so that when called without
-arguments, they result in nothing instead of a quoted empty string;
-this is so that it is possible to distinguish between no arguments and
-an empty first argument. `dquote', on the other hand, results in a
-string no matter what, since it is still possible to tell whether it
-was invoked without arguments based on the resulting string.
+arguments, they result in nothing instead of a quoted empty string; this
+is so that it is possible to distinguish between no arguments and an
+empty first argument. 'dquote', on the other hand, results in a string
+no matter what, since it is still possible to tell whether it was
+invoked without arguments based on the resulting string.
$ m4 -I examples
undivert(`quote.m4')dnl
=> ```$1'',$0(shift($@))')')
=>divert`'dnl
- It is worth pointing out that `quote(ARGS)' is more efficient than
-`joinall(`,', ARGS)' for producing the same output.
+ It is worth pointing out that 'quote(ARGS)' is more efficient than
+'joinall(`,', ARGS)' for producing the same output.
- One more useful macro based on `shift' allows portably selecting an
+ One more useful macro based on 'shift' allows portably selecting an
arbitrary argument (usually greater than the ninth argument), without
relying on the GNU extension of multi-digit arguments (*note
Arguments::).
-- Composite: argn (N, ...)
Expands to argument N out of the remaining arguments. N must be a
- positive number. Usually invoked as `argn(`N',$@)'.
+ positive number. Usually invoked as 'argn(`N',$@)'.
It is implemented as:
Takes the name in ITERATOR, which must be a valid macro name, and
successively assign it each integer value from START to END,
inclusive. For each assignment to ITERATOR, append TEXT to the
- expansion of the `forloop'. TEXT may refer to ITERATOR. Any
+ expansion of the 'forloop'. TEXT may refer to ITERATOR. Any
definition of ITERATOR prior to this invocation is restored.
It can, for example, be used for simple counting:
=> (4, 1) (4, 2) (4, 3) (4, 4) (4, 5) (4, 6) (4, 7) (4, 8)
=>
- The implementation of the `forloop' macro is fairly straightforward.
-The `forloop' macro itself is simply a wrapper, which saves the
-previous definition of the first argument, calls the internal macro
-`_forloop', and re-establishes the saved definition of the first
-argument.
+ The implementation of the 'forloop' macro is fairly straightforward.
+The 'forloop' macro itself is simply a wrapper, which saves the previous
+definition of the first argument, calls the internal macro '_forloop',
+and re-establishes the saved definition of the first argument.
- The macro `_forloop' expands the fourth argument once, and tests to
+ The macro '_forloop' expands the fourth argument once, and tests to
see if the iterator has reached the final value. If it has not
-finished, it increments the iterator (using the predefined macro
-`incr', *note Incr::), and recurses.
+finished, it increments the iterator (using the predefined macro 'incr',
+*note Incr::), and recurses.
- Here is an actual implementation of `forloop', distributed as
-`m4-1.4.16/examples/forloop.m4' in this package:
+ Here is an actual implementation of 'forloop', distributed as
+'m4-1.4.17/examples/forloop.m4' in this package:
$ m4 -I examples
undivert(`forloop.m4')dnl
arguments are left unquoted, and see what happens if they are quoted.
(As presented, these two macros are useful but not very robust for
general use. They lack even basic error handling for cases like START
-less than END, END not numeric, or ITERATOR not being a macro name.
-See if you can improve these macros; or *note Answers: Improved
-forloop.).
+less than END, END not numeric, or ITERATOR not being a macro name. See
+if you can improve these macros; or *note Answers: Improved forloop.).
\1f
File: m4.info, Node: Foreach, Next: Stacks, Prev: Forloop, Up: Conditionals
-- Composite: foreachq (ITERATOR, QUOTE-LIST, TEXT)
Takes the name in ITERATOR, which must be a valid macro name, and
successively assign it each value from PAREN-LIST or QUOTE-LIST.
- In `foreach', PAREN-LIST is a comma-separated list of elements
- contained in parentheses. In `foreachq', QUOTE-LIST is a
- comma-separated list of elements contained in a quoted string.
- For each assignment to ITERATOR, append TEXT to the overall
- expansion. TEXT may refer to ITERATOR. Any definition of
- ITERATOR prior to this invocation is restored.
+ In 'foreach', PAREN-LIST is a comma-separated list of elements
+ contained in parentheses. In 'foreachq', QUOTE-LIST is a
+ comma-separated list of elements contained in a quoted string. For
+ each assignment to ITERATOR, append TEXT to the overall expansion.
+ TEXT may refer to ITERATOR. Any definition of ITERATOR prior to
+ this invocation is restored.
As an example, this displays each word in a list inside of a
-sentence, using an implementation of `foreach' distributed as
-`m4-1.4.16/examples/foreach.m4', and `foreachq' in
-`m4-1.4.16/examples/foreachq.m4'.
+sentence, using an implementation of 'foreach' distributed as
+'m4-1.4.17/examples/foreach.m4', and 'foreachq' in
+'m4-1.4.17/examples/foreachq.m4'.
$ m4 -I examples
include(`foreach.m4')
esac
=>esac
- The implementation of the `foreach' macro is a bit more involved; it
-is a wrapper around two helper macros. First, `_arg1' is needed to
-grab the first element of a list. Second, `_foreach' implements the
+ The implementation of the 'foreach' macro is a bit more involved; it
+is a wrapper around two helper macros. First, '_arg1' is needed to grab
+the first element of a list. Second, '_foreach' implements the
recursion, successively walking through the original list. Here is a
-simple implementation of `foreach':
+simple implementation of 'foreach':
$ m4 -I examples
undivert(`foreach.m4')dnl
=>divert`'dnl
Unfortunately, that implementation is not robust to macro names as
-list elements. Each iteration of `_foreach' is stripping another layer
+list elements. Each iteration of '_foreach' is stripping another layer
of quotes, leading to erratic results if list elements are not already
-fully expanded. The first cut at implementing `foreachq' takes this
+fully expanded. The first cut at implementing 'foreachq' takes this
into account. Also, when using quoted elements in a PAREN-LIST, the
overall list must be quoted. A QUOTE-LIST has the nice property of
requiring fewer characters to create a list containing the same quoted
=>(b
=>c)
- Obviously, `foreachq' did a better job; here is its implementation:
+ Obviously, 'foreachq' did a better job; here is its implementation:
$ m4 -I examples
undivert(`foreachq.m4')dnl
=> `define(`$1', `_arg1($2)')$3`'$0(`$1', `shift($2)', `$3')')')
=>divert`'dnl
- Notice that `_foreachq' had to use the helper macro `quote' defined
-earlier (*note Shift::), to ensure that the embedded `ifelse' call does
+ Notice that '_foreachq' had to use the helper macro 'quote' defined
+earlier (*note Shift::), to ensure that the embedded 'ifelse' call does
not go haywire if a list element contains a comma. Unfortunately, this
-implementation of `foreachq' has its own severe flaw. Whereas the
-`foreach' implementation was linear, this macro is quadratic in the
+implementation of 'foreachq' has its own severe flaw. Whereas the
+'foreach' implementation was linear, this macro is quadratic in the
number of list elements, and is much more likely to trip up the limit
-set by the command line option `--nesting-limit' (or `-L', *note
+set by the command line option '--nesting-limit' (or '-L', *note
Invoking m4: Limits control.). Additionally, this implementation does
-not expand `defn(`ITERATOR')' very well, when compared with `foreach'.
+not expand 'defn(`ITERATOR')' very well, when compared with 'foreach'.
$ m4 -I examples
include(`foreach.m4')include(`foreachq.m4')
6.6 Working with definition stacks
==================================
-Thanks to `pushdef', manipulation of a stack is an intrinsic operation
-in `m4'. Normally, only the topmost definition in a stack is
-important, but sometimes, it is desirable to manipulate the entire
-definition stack.
+Thanks to 'pushdef', manipulation of a stack is an intrinsic operation
+in 'm4'. Normally, only the topmost definition in a stack is important,
+but sometimes, it is desirable to manipulate the entire definition
+stack.
-- Composite: stack_foreach (MACRO, ACTION)
-- Composite: stack_foreach_lifo (MACRO, ACTION)
- For each of the `pushdef' definitions associated with MACRO,
- invoke the macro ACTION with a single argument of that definition.
- `stack_foreach' visits the oldest definition first, while
- `stack_foreach_lifo' visits the current definition first. ACTION
+ For each of the 'pushdef' definitions associated with MACRO, invoke
+ the macro ACTION with a single argument of that definition.
+ 'stack_foreach' visits the oldest definition first, while
+ 'stack_foreach_lifo' visits the current definition first. ACTION
should not modify or dereference MACRO. There are a few special
- macros, such as `defn', which cannot be used as the MACRO
+ macros, such as 'defn', which cannot be used as the MACRO
parameter.
A sample implementation of these macros is distributed in the file
-`m4-1.4.16/examples/stack.m4'.
+'m4-1.4.17/examples/stack.m4'.
$ m4 -I examples
include(`stack.m4')
=>1
Now for the implementation. Note the definition of a helper macro,
-`_stack_reverse', which destructively swaps the contents of one stack
-of definitions into the reverse order in the temporary macro `tmp-$1'.
-By calling the helper twice, the original order is restored back into
-the macro `$1'; since the operation is destructive, this explains why
-`$1' must not be modified or dereferenced during the traversal. The
-caller can then inject additional code to pass the definition currently
-being visited to `$2'. The choice of helper names is intentional;
-since `-' is not valid as part of a macro name, there is no risk of
-conflict with a valid macro name, and the code is guaranteed to use
-`defn' where necessary. Finally, note that any macro used in the
-traversal of a `pushdef' stack, such as `pushdef' or `defn', cannot be
-handled by `stack_foreach', since the macro would temporarily be
-undefined during the algorithm.
+'_stack_reverse', which destructively swaps the contents of one stack of
+definitions into the reverse order in the temporary macro 'tmp-$1'. By
+calling the helper twice, the original order is restored back into the
+macro '$1'; since the operation is destructive, this explains why '$1'
+must not be modified or dereferenced during the traversal. The caller
+can then inject additional code to pass the definition currently being
+visited to '$2'. The choice of helper names is intentional; since '-'
+is not valid as part of a macro name, there is no risk of conflict with
+a valid macro name, and the code is guaranteed to use 'defn' where
+necessary. Finally, note that any macro used in the traversal of a
+'pushdef' stack, such as 'pushdef' or 'defn', cannot be handled by
+'stack_foreach', since the macro would temporarily be undefined during
+the algorithm.
$ m4 -I examples
undivert(`stack.m4')dnl
===============================
Since m4 is a macro language, it is possible to write macros that can
-build other macros. First on the list is a way to automate the
-creation of blind macros.
+build other macros. First on the list is a way to automate the creation
+of blind macros.
- -- Composite: define_blind (NAME, [VALUE])
+ -- Composite: define_blind (NAME, [VALUE]
Defines NAME as a blind macro, such that NAME will expand to VALUE
- only when given explicit arguments. VALUE should not be the
- result of `defn' (*note Defn::). This macro is only recognized
- with parameters, and results in an empty string.
+ only when given explicit arguments. VALUE should not be the result
+ of 'defn' (*note Defn::). This macro is only recognized with
+ parameters, and results in an empty string.
Defining a macro to define another macro can be a bit tricky. We
-want to use a literal `$#' in the argument to the nested `define'.
-However, if `$' and `#' are adjacent in the definition of
-`define_blind', then it would be expanded as the number of arguments to
-`define_blind' rather than the intended number of arguments to NAME.
-The solution is to pass the difficult characters through extra
-arguments to a helper macro `_define_blind'. When composing macros, it
-is a common idiom to need a helper macro to concatenate text that forms
-parameters in the composed macro, rather than interpreting the text as
-a parameter of the composing macro.
-
- As for the limitation against using `defn', there are two reasons.
-If a macro was previously defined with `define_blind', then it can
-safely be renamed to a new blind macro using plain `define'; using
-`define_blind' to rename it just adds another layer of `ifelse',
+want to use a literal '$#' in the argument to the nested 'define'.
+However, if '$' and '#' are adjacent in the definition of
+'define_blind', then it would be expanded as the number of arguments to
+'define_blind' rather than the intended number of arguments to NAME.
+The solution is to pass the difficult characters through extra arguments
+to a helper macro '_define_blind'. When composing macros, it is a
+common idiom to need a helper macro to concatenate text that forms
+parameters in the composed macro, rather than interpreting the text as a
+parameter of the composing macro.
+
+ As for the limitation against using 'defn', there are two reasons.
+If a macro was previously defined with 'define_blind', then it can
+safely be renamed to a new blind macro using plain 'define'; using
+'define_blind' to rename it just adds another layer of 'ifelse',
occupying memory and slowing down execution. And if a macro is a
-builtin, then it would result in an attempt to define a macro
-consisting of both text and a builtin token; this is not supported, and
-the builtin token is flattened to an empty string.
+builtin, then it would result in an attempt to define a macro consisting
+of both text and a builtin token; this is not supported, and the builtin
+token is flattened to an empty string.
With that explanation, here's the definition, and some sample usage.
-Notice that `define_blind' is itself a blind macro.
+Notice that 'define_blind' is itself a blind macro.
$ m4 -d
define(`define_blind', `ifelse(`$#', `0', ``$0'',
with the resulting list of arguments.
A demonstration of currying makes the intent of this macro a little
-more obvious. The macro `stack_foreach' mentioned earlier is an example
+more obvious. The macro 'stack_foreach' mentioned earlier is an example
of a context that provides exactly one argument to a macro name. But
-coupled with currying, we can invoke `reverse' with two arguments for
+coupled with currying, we can invoke 'reverse' with two arguments for
each definition of a macro stack. This example uses the file
-`m4-1.4.16/examples/curry.m4' included in the distribution.
+'m4-1.4.17/examples/curry.m4' included in the distribution.
$ m4 -I examples
include(`curry.m4')include(`stack.m4')
curry(`curry', `reverse', `1')(`2')(`3')
=>3, 2, 1
- Now for the implementation. Notice how `curry' leaves off with a
+ Now for the implementation. Notice how 'curry' leaves off with a
macro name but no open parenthesis, while still in the middle of
-collecting arguments for `$1'. The macro `_curry' is the helper macro
+collecting arguments for '$1'. The macro '_curry' is the helper macro
that takes one argument, then adds it to the list and finally supplies
-the closing parenthesis. The use of a comma inside the `shift' call
+the closing parenthesis. The use of a comma inside the 'shift' call
allows currying to also work for a macro that takes one argument,
although it often makes more sense to invoke that macro directly rather
-than going through `curry'.
+than going through 'curry'.
$ m4 -I examples
undivert(`curry.m4')dnl
=>define(`_curry', ``$1')')
=>divert`'dnl
- Unfortunately, with M4 1.4.x, `curry' is unable to handle builtin
+ Unfortunately, with M4 1.4.x, 'curry' is unable to handle builtin
tokens, which are silently flattened to the empty string when passed
through another text macro. This limitation will be lifted in a future
release of M4.
-- Composite: copy (SOURCE, DEST)
-- Composite: rename (SOURCE, DEST)
Ensure that DEST is undefined, then define it to the same stack of
- definitions currently in SOURCE. `copy' leaves SOURCE unchanged,
- while `rename' undefines SOURCE. There are only a few macros,
- such as `copy' or `defn', which cannot be copied via this macro.
+ definitions currently in SOURCE. 'copy' leaves SOURCE unchanged,
+ while 'rename' undefines SOURCE. There are only a few macros, such
+ as 'copy' or 'defn', which cannot be copied via this macro.
The implementation is relatively straightforward (although since it
-uses `curry', it is unable to copy builtin macros, such as the second
-definition of `a' as a synonym for `divnum'. See if you can design a
+uses 'curry', it is unable to copy builtin macros, such as the second
+definition of 'a' as a synonym for 'divnum'. See if you can design a
version that works around this limitation, or *note Answers: Improved
copy.).
7 How to debug macros and input
*******************************
-When writing macros for `m4', they often do not work as intended on the
+When writing macros for 'm4', they often do not work as intended on the
first try (as is the case with most programming languages).
-Fortunately, there is support for macro debugging in `m4'.
+Fortunately, there is support for macro debugging in 'm4'.
* Menu:
================================
If you want to see what a name expands into, you can use the builtin
-`dumpdef':
+'dumpdef':
- -- Builtin: dumpdef ([NAMES...])
+ -- Builtin: dumpdef ([NAMES...]
Accepts any number of arguments. If called without any arguments,
it displays the definitions of all known names, otherwise it
- displays the definitions of the NAMES given. The output is
- printed to the current debug file (usually standard error), and is
- sorted by name. If an unknown name is encountered, a warning is
- printed.
+ displays the definitions of the NAMES given. The output is printed
+ to the current debug file (usually standard error), and is sorted
+ by name. If an unknown name is encountered, a warning is printed.
- The expansion of `dumpdef' is void.
+ The expansion of 'dumpdef' is void.
$ m4 -d
define(`foo', `Hello world.')
=>
dumpdef(`foo')
- error-->foo: `Hello world.'
- =>
+ error->foo: =>
dumpdef(`define')
- error-->define: <define>
- =>
+ error->define: =>
The last example shows how builtin macros definitions are displayed.
The definition that is dumped corresponds to what would occur if the
pushdef(`f', ``$0'1')pushdef(`f', ``$0'2')
=>
f(popdef(`f')dumpdef(`f'))
- error-->f: ``$0'1'
- =>f2
+ error->f: =>f2
f(popdef(`f')dumpdef(`f'))
- error-->m4:stdin:3: undefined macro `f'
+ error->m4:stdin:3: undefined macro `f'
=>f1
*Note Debug Levels::, for information on controlling the details of
=======================
It is possible to trace macro calls and expansions through the builtins
-`traceon' and `traceoff':
+'traceon' and 'traceoff':
- -- Builtin: traceon ([NAMES...])
- -- Builtin: traceoff ([NAMES...])
- When called without any arguments, `traceon' and `traceoff' will
+ -- Builtin: traceon ([NAMES...]
+ -- Builtin: traceoff ([NAMES...]
+ When called without any arguments, 'traceon' and 'traceoff' will
turn tracing on and off, respectively, for all currently defined
macros.
When called with arguments, only the macros listed in NAMES are
affected, whether or not they are currently defined.
- The expansion of `traceon' and `traceoff' is void.
+ The expansion of 'traceon' and 'traceoff' is void.
Whenever a traced macro is called and the arguments have been
-collected, the call is displayed. If the expansion of the macro call
-is not void, the expansion can be displayed after the call. The output
-is printed to the current debug file (defaulting to standard error,
-*note Debug Output::).
+collected, the call is displayed. If the expansion of the macro call is
+not void, the expansion can be displayed after the call. The output is
+printed to the current debug file (defaulting to standard error, *note
+Debug Output::).
$ m4 -d
define(`foo', `Hello World.')
traceon(`foo', `echo')
=>
foo
- error-->m4trace: -1- foo -> `Hello World.'
+ error->m4trace: -1- foo -> `Hello World.'
=>Hello World.
echo(`gnus', `and gnats')
- error-->m4trace: -1- echo(`gnus', `and gnats') -> ``gnus',`and gnats''
+ error->m4trace: -1- echo(`gnus', `and gnats') -> ``gnus',`and gnats''
=>gnus,and gnats
The number between dashes is the depth of the expansion. It is one
most of the time, signifying an expansion at the outermost level, but it
increases when macro arguments contain unquoted macro calls. The
maximum number that will appear between dashes is controlled by the
-option `--nesting-limit' (or `-L', *note Invoking m4: Limits control.).
-Additionally, the option `--trace' (or `-t') can be used to invoke
-`traceon(NAME)' before parsing input.
+option '--nesting-limit' (or '-L', *note Invoking m4: Limits control.).
+Additionally, the option '--trace' (or '-t') can be used to invoke
+'traceon(NAME)' before parsing input.
$ m4 -L 3 -t ifelse
ifelse(`one level')
- error-->m4trace: -1- ifelse
+ error->m4trace: -1- ifelse
=>
ifelse(ifelse(ifelse(`three levels')))
- error-->m4trace: -3- ifelse
- error-->m4trace: -2- ifelse
- error-->m4trace: -1- ifelse
+ error->m4trace: -3- ifelse
+ error->m4trace: -2- ifelse
+ error->m4trace: -1- ifelse
=>
ifelse(ifelse(ifelse(ifelse(`four levels'))))
- error-->m4:stdin:3: recursion limit of 3 exceeded, use -L<N> to change it
+ error->m4:stdin:3: recursion limit of 3 exceeded, use -L<N> to change it
Tracing by name is an attribute that is preserved whether the macro
is defined or not. This allows the selection of macros to trace before
define(`foo', `bar')
=>
foo
- error-->m4trace: -1- foo -> `bar'
+ error->m4trace: -1- foo -> `bar'
=>bar
undefine(`foo')
=>
ifdef(`foo', `yes', `no')
=>no
indir(`foo')
- error-->m4:stdin:9: undefined macro `foo'
+ error->m4:stdin:9: undefined macro `foo'
=>
define(`foo', `blah')
=>
foo
- error-->m4trace: -1- foo -> `blah'
+ error->m4trace: -1- foo -> `blah'
=>blah
traceoff
=>
foo
=>blah
- Tracing even works on builtins. However, `defn' (*note Defn::) does
+ Tracing even works on builtins. However, 'defn' (*note Defn::) does
not transfer tracing status.
$ m4 -d
traceon(`traceon')
=>
traceon(`traceoff')
- error-->m4trace: -1- traceon(`traceoff')
+ error->m4trace: -1- traceon(`traceoff')
=>
traceoff(`traceoff')
- error-->m4trace: -1- traceoff(`traceoff')
+ error->m4trace: -1- traceoff(`traceoff')
=>
traceoff(`traceon')
=>
define(`m4_divnum', defn(`divnum'))
=>
eval(divnum)
- error-->m4trace: -1- eval(`0') -> `0'
+ error->m4trace: -1- eval(`0') -> `0'
=>0
m4_eval(m4_divnum)
- error-->m4trace: -2- m4_divnum -> `0'
+ error->m4trace: -2- m4_divnum -> `0'
=>0
*Note Debug Levels::, for information on controlling the details of
the display. The format of the trace output is not specified by POSIX,
-and varies between implementations of `m4'.
+and varies between implementations of 'm4'.
\1f
File: m4.info, Node: Debug Levels, Next: Debug Output, Prev: Trace, Up: Debugging
7.3 Controlling debugging output
================================
-The `-d' option to `m4' (or `--debug', *note Invoking m4: Debugging
+The '-d' option to 'm4' (or '--debug', *note Invoking m4: Debugging
options.) controls the amount of details presented in three categories
-of output. Trace output is requested by `traceon' (*note Trace::), and
-each line is prefixed by `m4trace:' in relation to a macro invocation.
+of output. Trace output is requested by 'traceon' (*note Trace::), and
+each line is prefixed by 'm4trace:' in relation to a macro invocation.
Debug output tracks useful events not associated with a macro
-invocation, and each line is prefixed by `m4debug:'. Finally,
-`dumpdef' (*note Dumpdef::) output is affected, with no prefix added to
-the output lines.
+invocation, and each line is prefixed by 'm4debug:'. Finally, 'dumpdef'
+(*note Dumpdef::) output is affected, with no prefix added to the output
+lines.
The FLAGS following the option can be one or more of the following:
-`a'
+'a'
In trace output, show the actual arguments that were collected
before invoking the macro. This applies to all macro calls if the
- `t' flag is used, otherwise only the macros covered by calls of
- `traceon'. Arguments are subject to length truncation specified by
- the command line option `--arglength' (or `-l').
+ 't' flag is used, otherwise only the macros covered by calls of
+ 'traceon'. Arguments are subject to length truncation specified by
+ the command line option '--arglength' (or '-l').
-`c'
+'c'
In trace output, show several trace lines for each macro call. A
line is shown when the macro is seen, but before the arguments are
- collected; a second line when the arguments have been collected
- and a third line after the call has completed.
+ collected; a second line when the arguments have been collected and
+ a third line after the call has completed.
-`e'
+'e'
In trace output, show the expansion of each macro call, if it is
- not void. This applies to all macro calls if the `t' flag is used,
- otherwise only the macros covered by calls of `traceon'. The
+ not void. This applies to all macro calls if the 't' flag is used,
+ otherwise only the macros covered by calls of 'traceon'. The
expansion is subject to length truncation specified by the command
- line option `--arglength' (or `-l').
+ line option '--arglength' (or '-l').
-`f'
+'f'
In debug and trace output, include the name of the current input
file in the output line.
-`i'
+'i'
In debug output, print a message each time the current input file
is changed.
-`l'
- In debug and trace output, include the current input line number
- in the output line.
+'l'
+ In debug and trace output, include the current input line number in
+ the output line.
-`p'
- In debug output, print a message when a named file is found
- through the path search mechanism (*note Search Path::), giving
- the actual file name used.
+'p'
+ In debug output, print a message when a named file is found through
+ the path search mechanism (*note Search Path::), giving the actual
+ file name used.
-`q'
+'q'
In trace and dumpdef output, quote actual arguments and macro
expansions in the display with the current quotes. This is useful
- in connection with the `a' and `e' flags above.
+ in connection with the 'a' and 'e' flags above.
-`t'
+'t'
In trace output, trace all macro calls made in this invocation of
- `m4', regardless of the settings of `traceon'.
+ 'm4', regardless of the settings of 'traceon'.
-`x'
- In trace output, add a unique `macro call id' to each line of the
- trace output. This is useful in connection with the `c' flag
+'x'
+ In trace output, add a unique 'macro call id' to each line of the
+ trace output. This is useful in connection with the 'c' flag
above.
-`V'
+'V'
A shorthand for all of the above flags.
- If no flags are specified with the `-d' option, the default is
-`aeq'. The examples throughout this manual assume the default flags.
+ If no flags are specified with the '-d' option, the default is 'aeq'.
+The examples throughout this manual assume the default flags.
- There is a builtin macro `debugmode', which allows on-the-fly
-control of the debugging output format:
+ There is a builtin macro 'debugmode', which allows on-the-fly control
+of the debugging output format:
- -- Builtin: debugmode ([FLAGS])
+ -- Builtin: debugmode ([FLAGS]
The argument FLAGS should be a subset of the letters listed above.
- As special cases, if the argument starts with a `+', the flags are
- added to the current debug flags, and if it starts with a `-', they
+ As special cases, if the argument starts with a '+', the flags are
+ added to the current debug flags, and if it starts with a '-', they
are removed. If no argument is present, all debugging flags are
- cleared (as if no `-d' was given), and with an empty argument the
- flags are reset to the default of `aeq'.
+ cleared (as if no '-d' was given), and with an empty argument the
+ flags are reset to the default of 'aeq'.
- The expansion of `debugmode' is void.
+ The expansion of 'debugmode' is void.
$ m4
define(`foo', `FOO')
debugmode()
=>
foo
- error-->m4trace: -1- foo -> `FOO'
+ error->m4trace: -1- foo -> `FOO'
=>FOO
debugmode
=>
foo
- error-->m4trace: -1- foo
+ error->m4trace: -1- foo
=>FOO
debugmode(`+l')
=>
foo
- error-->m4trace:8: -1- foo
+ error->m4trace:8: -1- foo
=>FOO
The following example demonstrates the behavior of length truncation,
define(`echo', `$@')debugmode(`+t')
=>
echo(`1', `long string')
- error-->m4trace: -1- echo(`1', `long s...') -> ``1',`l...'
+ error->m4trace: -1- echo(`1', `long s...') -> ``1',`l...'
=>1,long string
indir(`echo', defn(`changequote'))
- error-->m4trace: -2- defn(`change...')
- error-->m4trace: -1- indir(`echo', <changequote>) -> ``''
+ error->m4trace: -2- defn(`change...')
+ error->m4trace: -1- indir(`echo', <changequote>) -> ``''
=>
This example shows the effects of the debug flags that are not
related to macro tracing.
$ m4 -dip -I examples
- error-->m4debug: input read from stdin
+ error->m4debug: input read from stdin
include(`foo')dnl
- error-->m4debug: path search for `foo' found `examples/foo'
- error-->m4debug: input read from examples/foo
+ error->m4debug: path search for `foo' found `examples/foo'
+ error->m4debug: input read from examples/foo
=>bar
- error-->m4debug: input reverted to stdin, line 1
+ error->m4debug: input reverted to stdin, line 1
^D
- error-->m4debug: input exhausted
+ error->m4debug: input exhausted
\1f
File: m4.info, Node: Debug Output, Prev: Debug Levels, Up: Debugging
===========================
Debug and tracing output can be redirected to files using either the
-`--debugfile' option to `m4' (*note Invoking m4: Debugging options.),
-or with the builtin macro `debugfile':
+'--debugfile' option to 'm4' (*note Invoking m4: Debugging options.), or
+with the builtin macro 'debugfile':
- -- Builtin: debugfile ([FILE])
+ -- Builtin: debugfile ([FILE]
Sends all further debug and trace output to FILE, opened in append
mode. If FILE is the empty string, debug and trace output are
- discarded. If `debugfile' is called without any arguments, debug
+ discarded. If 'debugfile' is called without any arguments, debug
and trace output are sent to standard error. This does not affect
- warnings, error messages, or `errprint' output, which are always
+ warnings, error messages, or 'errprint' output, which are always
sent to standard error. If FILE cannot be opened, the current
debug file is unchanged, and an error is issued.
- The expansion of `debugfile' is void.
+ The expansion of 'debugfile' is void.
$ m4 -d
traceon(`divnum')
=>
divnum(`extra')
- error-->m4:stdin:2: Warning: excess arguments to builtin `divnum' ignored
- error-->m4trace: -1- divnum(`extra') -> `0'
+ error->m4:stdin:2: Warning: excess arguments to builtin `divnum' ignored
+ error->m4trace: -1- divnum(`extra') -> `0'
=>0
debugfile()
=>
divnum(`extra')
- error-->m4:stdin:4: Warning: excess arguments to builtin `divnum' ignored
+ error->m4:stdin:4: Warning: excess arguments to builtin `divnum' ignored
=>0
debugfile
=>
divnum
- error-->m4trace: -1- divnum -> `0'
+ error->m4trace: -1- divnum -> `0'
=>0
\1f
***************
This chapter describes various builtin macros for controlling the input
-to `m4'.
+to 'm4'.
* Menu:
8.1 Deleting whitespace in input
================================
-The builtin `dnl' stands for "Discard to Next Line":
+The builtin 'dnl' stands for "Discard to Next Line":
-- Builtin: dnl
All characters, up to and including the next newline, are discarded
- without performing any macro expansion. A warning is issued if
- the end of the file is encountered without a newline.
+ without performing any macro expansion. A warning is issued if the
+ end of the file is encountered without a newline.
- The expansion of `dnl' is void.
+ The expansion of 'dnl' is void.
- It is often used in connection with `define', to remove the newline
-that follows the call to `define'. Thus
+ It is often used in connection with 'define', to remove the newline
+that follows the call to 'define'. Thus
define(`foo', `Macro `foo'.')dnl A very simple macro, indeed.
foo
The input up to and including the next newline is discarded, as
opposed to the way comments are treated (*note Comments::).
- Usually, `dnl' is immediately followed by an end of line or some
-other whitespace. GNU `m4' will produce a warning diagnostic if `dnl'
-is followed by an open parenthesis. In this case, `dnl' will collect
+ Usually, 'dnl' is immediately followed by an end of line or some
+other whitespace. GNU 'm4' will produce a warning diagnostic if 'dnl'
+is followed by an open parenthesis. In this case, 'dnl' will collect
and process all arguments, looking for a matching close parenthesis.
All predictable side effects resulting from this collection will take
-place. `dnl' will return no output. The input following the matching
-close parenthesis up to and including the next newline, on whatever
-line containing it, will still be discarded.
+place. 'dnl' will return no output. The input following the matching
+close parenthesis up to and including the next newline, on whatever line
+containing it, will still be discarded.
dnl(`args are ignored, but side effects occur',
define(`foo', `like this')) while this text is ignored: undefine(`foo')
- error-->m4:stdin:1: Warning: excess arguments to builtin `dnl' ignored
+ error->m4:stdin:1: Warning: excess arguments to builtin `dnl' ignored
See how `foo' was defined, foo?
=>See how foo was defined, like this?
define(`hi', `HI')
=>
^D
- error-->m4:stdin:1: Warning: end of file treated as newline
+ error->m4:stdin:1: Warning: end of file treated as newline
=>0 HI 2 HI
\1f
=================================
The default quote delimiters can be changed with the builtin
-`changequote':
+'changequote':
- -- Builtin: changequote ([START = ``'], [END = `''])
- This sets START as the new begin-quote delimiter and END as the
- new end-quote delimiter. If both arguments are missing, the
- default quotes (``' and `'') are used. If START is void, then
- quoting is disabled. Otherwise, if END is missing or void, the
- default end-quote delimiter (`'') is used. The quote delimiters
- can be of any length.
+ -- Builtin: changequote ([START = '`']
+ This sets START as the new begin-quote delimiter and END as the new
+ end-quote delimiter. If both arguments are missing, the default
+ quotes ('`' and ''') are used. If START is void, then quoting is
+ disabled. Otherwise, if END is missing or void, the default
+ end-quote delimiter (''') is used. The quote delimiters can be of
+ any length.
- The expansion of `changequote' is void.
+ The expansion of 'changequote' is void.
changequote(`[', `]')
=>
foo
=>Macro foo.
- The quotation strings can safely contain eight-bit characters. If
-no single character is appropriate, START and END can be of any length.
+ The quotation strings can safely contain eight-bit characters. If no
+single character is appropriate, START and END can be of any length.
Other implementations cap the delimiter length to five characters, but
GNU has no inherent limit.
foo
=>Macro [[foo]].
- Calling `changequote' with START as the empty string will
-effectively disable the quoting mechanism, leaving no way to quote text.
-However, using an empty string is not portable, as some other
-implementations of `m4' revert to the default quoting, while others
-preserve the prior non-empty delimiter. If START is not empty, then an
-empty END will use the default end-quote delimiter of `'', as
-otherwise, it would be impossible to end a quoted string. Again, this
-is not portable, as some other `m4' implementations reuse START as the
-end-quote delimiter, while others preserve the previous non-empty
-value. Omitting both arguments restores the default begin-quote and
-end-quote delimiters; fortunately this behavior is portable to all
-implementations of `m4'.
+ Calling 'changequote' with START as the empty string will effectively
+disable the quoting mechanism, leaving no way to quote text. However,
+using an empty string is not portable, as some other implementations of
+'m4' revert to the default quoting, while others preserve the prior
+non-empty delimiter. If START is not empty, then an empty END will use
+the default end-quote delimiter of ''', as otherwise, it would be
+impossible to end a quoted string. Again, this is not portable, as some
+other 'm4' implementations reuse START as the end-quote delimiter, while
+others preserve the previous non-empty value. Omitting both arguments
+restores the default begin-quote and end-quote delimiters; fortunately
+this behavior is portable to all implementations of 'm4'.
define(`foo', `Macro `FOO'.')
=>
foo
=>Macro FOO.
- There is no way in `m4' to quote a string containing an unmatched
-begin-quote, except using `changequote' to change the current quotes.
+ There is no way in 'm4' to quote a string containing an unmatched
+begin-quote, except using 'changequote' to change the current quotes.
- If the quotes should be changed from, say, `[' to `[[', temporary
+ If the quotes should be changed from, say, '[' to '[[', temporary
quote characters have to be defined. To achieve this, two calls of
-`changequote' must be made, one for the temporary quotes and one for
-the new quotes.
+'changequote' must be made, one for the temporary quotes and one for the
+new quotes.
Macros are recognized in preference to the begin-quote string, so if
a prefix of START can be recognized as part of a potential macro name,
the quoting mechanism is effectively disabled. Unless you use
-`changeword' (*note Changeword::), this means that START should not
-begin with a letter, digit, or `_' (underscore). However, even though
+'changeword' (*note Changeword::), this means that START should not
+begin with a letter, digit, or '_' (underscore). However, even though
quoted strings are not recognized, the quote characters can still be
discerned in macro expansion and in trace output.
=>HI hi
Quotes are recognized in preference to argument collection. In
-particular, if START is a single `(', then argument collection is
-effectively disabled. For portability with other implementations, it
-is a good idea to avoid `(', `,', and `)' as the first character in
-START.
+particular, if START is a single '(', then argument collection is
+effectively disabled. For portability with other implementations, it is
+a good idea to avoid '(', ',', and ')' as the first character in START.
define(`echo', `$#:$@:')
=>
echo(hi,hi)bye)
=>1:HIhibye:
- However, if you are not worried about portability, using `(' and `)'
+ However, if you are not worried about portability, using '(' and ')'
as quoting characters has an interesting property--you can use it to
compute a quoted string containing the expansion of any quoted text, as
long as the expansion results in both balanced quotes and balanced
-parentheses. The trick is realizing `expand' uses `$1' unquoted, to
+parentheses. The trick is realizing 'expand' uses '$1' unquoted, to
trigger its expansion using the normal quoting characters, but uses
extra parentheses to group unquoted commas that occur in the expansion
-without consuming whitespace following those commas. Then `_expand'
-uses `changequote' to convert the extra parentheses back into quoting
-characters. Note that it takes two more `changequote' invocations to
+without consuming whitespace following those commas. Then '_expand'
+uses 'changequote' to convert the extra parentheses back into quoting
+characters. Note that it takes two more 'changequote' invocations to
restore the original quotes. Contrast the behavior on whitespace when
-using `$*', via `quote', to attempt the same task.
+using '$*', via 'quote', to attempt the same task.
changequote(`[', `]')dnl
define([a], [1, (b)])dnl
If END is a prefix of START, the end-quote will be recognized in
preference to a nested begin-quote. In particular, changing the quotes
to have the same string for START and END disables nesting of quotes.
-When quote nesting is disabled, it is impossible to double-quote
-strings across macro expansions, so using the same string is not done
-very often.
+When quote nesting is disabled, it is impossible to double-quote strings
+across macro expansions, so using the same string is not done very
+often.
define(`hi', `HI')
=>
=>hello world
`dangling quote
^D
- error-->m4:stdin:2: ERROR: end of file in string
+ error->m4:stdin:2: ERROR: end of file in string
ifelse(`dangling quote
^D
- error-->m4:stdin:1: ERROR: end of file in string
+ error->m4:stdin:1: ERROR: end of file in string
\1f
File: m4.info, Node: Changecom, Next: Changeword, Prev: Changequote, Up: Input Control
===================================
The default comment delimiters can be changed with the builtin macro
-`changecom':
+'changecom':
- -- Builtin: changecom ([START], [END = `<NL>'])
+ -- Builtin: changecom ([START]
This sets START as the new begin-comment delimiter and END as the
- new end-comment delimiter. If both arguments are missing, or
- START is void, then comments are disabled. Otherwise, if END is
- missing or void, the default end-comment delimiter of newline is
- used. The comment delimiters can be of any length.
+ new end-comment delimiter. If both arguments are missing, or START
+ is void, then comments are disabled. Otherwise, if END is missing
+ or void, the default end-comment delimiter of newline is used. The
+ comment delimiters can be of any length.
- The expansion of `changecom' is void.
+ The expansion of 'changecom' is void.
define(`comment', `COMMENT')
=>
quoted strings. If you want the text inside a comment expanded, quote
the begin-comment delimiter.
- Calling `changecom' without any arguments, or with START as the
-empty string, will effectively disable the commenting mechanism. To
-restore the original comment start of `#', you must explicitly ask for
-it. If START is not empty, then an empty END will use the default
-end-comment delimiter of newline, as otherwise, it would be impossible
-to end a comment. However, this is not portable, as some other `m4'
+ Calling 'changecom' without any arguments, or with START as the empty
+string, will effectively disable the commenting mechanism. To restore
+the original comment start of '#', you must explicitly ask for it. If
+START is not empty, then an empty END will use the default end-comment
+delimiter of newline, as otherwise, it would be impossible to end a
+comment. However, this is not portable, as some other 'm4'
implementations preserve the previous non-empty delimiters instead.
define(`comment', `COMMENT')
not compatible with other implementations, where macros and even quoting
takes precedence over comments, so it may change in a future release.
For portability, this means that START should not begin with a letter,
-digit, or `_' (underscore), and that neither the start-quote nor the
+digit, or '_' (underscore), and that neither the start-quote nor the
start-comment string should be a prefix of the other.
define(`hi', `HI')
=>HI 1hi2
Comments are recognized in preference to argument collection. In
-particular, if START is a single `(', then argument collection is
-effectively disabled. For portability with other implementations, it
-is a good idea to avoid `(', `,', and `)' as the first character in
-START.
+particular, if START is a single '(', then argument collection is
+effectively disabled. For portability with other implementations, it is
+a good idea to avoid '(', ',', and ')' as the first character in START.
define(`echo', `$#:$*:$@:')
=>
=>
/*dangling comment
^D
- error-->m4:stdin:2: ERROR: end of file in comment
+ error->m4:stdin:2: ERROR: end of file in comment
\1f
File: m4.info, Node: Changeword, Next: M4wrap, Prev: Changecom, Up: Input Control
8.4 Changing the lexical structure of words
===========================================
- The macro `changeword' and all associated functionality is
- experimental. It is only available if the `--enable-changeword'
- option was given to `configure', at GNU `m4' installation time.
+ The macro 'changeword' and all associated functionality is
+ experimental. It is only available if the '--enable-changeword'
+ option was given to 'configure', at GNU 'm4' installation time.
The functionality will go away in the future, to be replaced by
other new features that are more efficient at providing the same
capabilities. _Do not rely on it_. Please direct your comments
about it the same way you would do for bugs.
- A file being processed by `m4' is split into quoted strings, words
+ A file being processed by 'm4' is split into quoted strings, words
(potential macro names) and simple tokens (any other single character).
Initially a word is defined by the following regular expression:
[_a-zA-Z][_a-zA-Z0-9]*
- Using `changeword', you can change this regular expression:
+ Using 'changeword', you can change this regular expression:
-- Optional builtin: changeword (REGEX)
Changes the regular expression for recognizing macro names to be
- REGEX. If REGEX is empty, use `[_a-zA-Z][_a-zA-Z0-9]*'. REGEX
+ REGEX. If REGEX is empty, use '[_a-zA-Z][_a-zA-Z0-9]*'. REGEX
must obey the constraint that every prefix of the desired final
pattern is also accepted by the regular expression. If REGEX
contains grouping parentheses, the macro invoked is the portion
that matched the first group, rather than the entire matching
string.
- The expansion of `changeword' is void. The macro `changeword' is
+ The expansion of 'changeword' is void. The macro 'changeword' is
recognized only with parameters.
- Relaxing the lexical rules of `m4' might be useful (for example) if
+ Relaxing the lexical rules of 'm4' might be useful (for example) if
you wanted to apply translations to a file of numbers:
ifdef(`changeword', `', `errprint(` skipping: no changeword support
=>hi
=>
- Because `m4' constructs its words a character at a time, there is a
+ Because 'm4' constructs its words a character at a time, there is a
restriction on the regular expressions that may be passed to
-`changeword'. This is that if your regular expression accepts `foo',
-it must also accept `f' and `fo'.
+'changeword'. This is that if your regular expression accepts 'foo', it
+must also accept 'f' and 'fo'.
ifdef(`changeword', `', `errprint(` skipping: no changeword support
')m4exit(`77')')dnl
foo
=>bar
- `changeword' has another function. If the regular expression
+ 'changeword' has another function. If the regular expression
supplied contains any grouped subexpressions, then text outside the
first of these is discarded before symbol lookup. So:
=>foo bar
=>
- `m4' now requires a `#' mark at the beginning of every macro
-invocation, so one can use `m4' to preprocess plain text without losing
-various words like `divert'.
+ 'm4' now requires a '#' mark at the beginning of every macro
+invocation, so one can use 'm4' to preprocess plain text without losing
+various words like 'divert'.
- In `m4', macro substitution is based on text, while in TeX, it is
-based on tokens. `changeword' can throw this difference into relief.
-For example, here is the same idea represented in TeX and `m4'. First,
+ In 'm4', macro substitution is based on text, while in TeX, it is
+based on tokens. 'changeword' can throw this difference into relief.
+For example, here is the same idea represented in TeX and 'm4'. First,
the TeX version:
\def\a{\message{Hello}}
@bye
=>Hello
-Then, the `m4' version:
+Then, the 'm4' version:
ifdef(`changeword', `', `errprint(` skipping: no changeword support
')m4exit(`77')')dnl
@a
=>errprint(Hello)
- In the TeX example, the first line defines a macro `a' to print the
-message `Hello'. The second line defines <@> to be usable instead of
+ In the TeX example, the first line defines a macro 'a' to print the
+message 'Hello'. The second line defines <@> to be usable instead of
<\> as an escape character. The third line defines <\> to be a normal
printing character, not an escape. The fourth line invokes the macro
-`a'. So, when TeX is run on this file, it displays the message `Hello'.
+'a'. So, when TeX is run on this file, it displays the message 'Hello'.
- When the `m4' example is passed through `m4', it outputs
-`errprint(Hello)'. The reason for this is that TeX does lexical
-analysis of macro definition when the macro is _defined_. `m4' just
+ When the 'm4' example is passed through 'm4', it outputs
+'errprint(Hello)'. The reason for this is that TeX does lexical
+analysis of macro definition when the macro is _defined_. 'm4' just
stores the text, postponing the lexical analysis until the macro is
_used_.
- You should note that using `changeword' will slow `m4' down by a
+ You should note that using 'changeword' will slow 'm4' down by a
factor of about seven, once it is changed to something other than the
-default regular expression. You can invoke `changeword' with the empty
+default regular expression. You can invoke 'changeword' with the empty
string to restore the default word definition, and regain the parsing
speed.
8.5 Saving text until end of input
==================================
-It is possible to `save' some text until the end of the normal input has
-been seen. Text can be saved, to be read again by `m4' when the normal
+It is possible to 'save' some text until the end of the normal input has
+been seen. Text can be saved, to be read again by 'm4' when the normal
input has been exhausted. This feature is normally used to initiate
cleanup actions before normal exit, e.g., deleting temporary files.
- To save input text, use the builtin `m4wrap':
+ To save input text, use the builtin 'm4wrap':
-- Builtin: m4wrap (STRING, ...)
Stores STRING in a safe place, to be reread when end of input is
- reached. As a GNU extension, additional arguments are
- concatenated with a space to the STRING.
+ reached. As a GNU extension, additional arguments are concatenated
+ with a space to the STRING.
- The expansion of `m4wrap' is void. The macro `m4wrap' is
+ The expansion of 'm4wrap' is void. The macro 'm4wrap' is
recognized only with parameters.
define(`cleanup', `This is the `cleanup' action.
=>This is the cleanup action.
The saved input is only reread when the end of normal input is seen,
-and not if `m4exit' is used to exit `m4'.
+and not if 'm4exit' is used to exit 'm4'.
- It is safe to call `m4wrap' from saved text, but then the order in
-which the saved text is reread is undefined. If `m4wrap' is not used
+ It is safe to call 'm4wrap' from saved text, but then the order in
+which the saved text is reread is undefined. If 'm4wrap' is not used
recursively, the saved pieces of text are reread in the opposite order
in which they were saved (LIFO--last in, first out). However, this
-behavior is likely to change in a future release, to match POSIX, so
-you should not depend on this order.
+behavior is likely to change in a future release, to match POSIX, so you
+should not depend on this order.
It is possible to emulate POSIX behavior even with older versions of
-GNU M4 by including the file `m4-1.4.16/examples/wrapfifo.m4' from the
+GNU M4 by including the file 'm4-1.4.17/examples/wrapfifo.m4' from the
distribution:
$ m4 -I examples
=>abc
It is likewise possible to emulate LIFO behavior without resorting to
-the GNU M4 extension of `builtin', by including the file
-`m4-1.4.16/examples/wraplifo.m4' from the distribution.
-(Unfortunately, both examples shown here share some subtle bugs. See
-if you can find and correct them; or *note Answers: Improved m4wrap.).
+the GNU M4 extension of 'builtin', by including the file
+'m4-1.4.17/examples/wraplifo.m4' from the distribution. (Unfortunately,
+both examples shown here share some subtle bugs. See if you can find
+and correct them; or *note Answers: Improved m4wrap.).
$ m4 -I examples
undivert(`wraplifo.m4')dnl
=>bac
Here is an example of implementing a factorial function using
-`m4wrap':
+'m4wrap':
define(`f', `ifelse(`$1', `0', `Answer: 0!=1
', eval(`$1>1'), `0', `Answer: $2$1=eval(`$2$1')
^D
=>Answer: 10*9*8*7*6*5*4*3*2*1=3628800
- Invocations of `m4wrap' at the same recursion level are concatenated
+ Invocations of 'm4wrap' at the same recursion level are concatenated
and rescanned as usual:
define(`aa', `AA
m4wrap(`m4wrap(`)')len(abc')
=>
^D
- error-->m4:stdin:1: ERROR: end of file in argument list
+ error->m4:stdin:1: ERROR: end of file in argument list
\1f
File: m4.info, Node: File Inclusion, Next: Diversions, Prev: Input Control, Up: Top
9 File inclusion
****************
-`m4' allows you to include named files at any point in the input.
+'m4' allows you to include named files at any point in the input.
* Menu:
9.1 Including named files
=========================
-There are two builtin macros in `m4' for including files:
+There are two builtin macros in 'm4' for including files:
-- Builtin: include (FILE)
-- Builtin: sinclude (FILE)
- Both macros cause the file named FILE to be read by `m4'. When
- the end of the file is reached, input is resumed from the previous
+ Both macros cause the file named FILE to be read by 'm4'. When the
+ end of the file is reached, input is resumed from the previous
input file.
- The expansion of `include' and `sinclude' is therefore the
- contents of FILE.
+ The expansion of 'include' and 'sinclude' is therefore the contents
+ of FILE.
If FILE does not exist, is a directory, or cannot otherwise be
- read, the expansion is void, and `include' will fail with an error
- while `sinclude' is silent. The empty string counts as a file
- that does not exist.
+ read, the expansion is void, and 'include' will fail with an error
+ while 'sinclude' is silent. The empty string counts as a file that
+ does not exist.
- The macros `include' and `sinclude' are recognized only with
+ The macros 'include' and 'sinclude' are recognized only with
parameters.
include(`none')
- error-->m4:stdin:1: cannot open `none': No such file or directory
+ error->m4:stdin:1: cannot open `none': No such file or directory
=>
include()
- error-->m4:stdin:2: cannot open `': No such file or directory
+ error->m4:stdin:2: cannot open `': No such file or directory
=>
sinclude(`none')
=>
sinclude()
=>
- The rest of this section assumes that `m4' is invoked with the `-I'
-option (*note Invoking m4: Preprocessor features.) pointing to the
-`m4-1.4.16/examples' directory shipped as part of the GNU `m4' package.
-The file `m4-1.4.16/examples/incl.m4' in the distribution contains the
+ The rest of this section assumes that 'm4' is invoked with the '-I'
+option (*note Invoking m4: Preprocessor features.) pointing to the
+'m4-1.4.17/examples' directory shipped as part of the GNU 'm4' package.
+The file 'm4-1.4.17/examples/incl.m4' in the distribution contains the
lines:
$ cat examples/incl.m4
=>foo
=>Include file end
- Normally file inclusion is used to insert the contents of a file
-into the input stream. The contents of the file will be read by `m4'
-and macro calls in the file will be expanded:
+ Normally file inclusion is used to insert the contents of a file into
+the input stream. The contents of the file will be read by 'm4' and
+macro calls in the file will be expanded:
$ m4 -I examples
define(`foo', `FOO')
=>Include file end
=>
- The fact that `include' and `sinclude' expand to the contents of the
-file can be used to define macros that operate on entire files. Here
-is an example, which defines `bar' to expand to the contents of
-`incl.m4':
+ The fact that 'include' and 'sinclude' expand to the contents of the
+file can be used to define macros that operate on entire files. Here is
+an example, which defines 'bar' to expand to the contents of 'incl.m4':
$ m4 -I examples
define(`bar', include(`incl.m4'))
=>Include file end
=><<
- This use of `include' is not trivial, though, as files can contain
+ This use of 'include' is not trivial, though, as files can contain
quotes, commas, and parentheses, which can interfere with the way the
-`m4' parser works. GNU `m4' seamlessly concatenates the file contents
+'m4' parser works. GNU 'm4' seamlessly concatenates the file contents
with the next character, even if the included file ended in the middle
of a comment, string, or macro call. These conditions are only treated
as end of file errors if specified as input files on the command line.
- In GNU `m4', an alternative method of reading files is using
-`undivert' (*note Undivert::) on a named file.
+ In GNU 'm4', an alternative method of reading files is using
+'undivert' (*note Undivert::) on a named file.
\1f
File: m4.info, Node: Search Path, Prev: Include, Up: File Inclusion
9.2 Searching for include files
===============================
-GNU `m4' allows included files to be found in other directories than
-the current working directory.
+GNU 'm4' allows included files to be found in other directories than the
+current working directory.
- If the `--prepend-include' or `-B' command-line option was provided
+ If the '--prepend-include' or '-B' command-line option was provided
(*note Invoking m4: Preprocessor features.), those directories are
searched first, in reverse order that those options were listed on the
-command line. Then `m4' looks in the current working directory. Next
-comes the directories specified with the `--include' or `-I' option, in
-the order found on the command line. Finally, if the `M4PATH'
-environment variable is set, it is expected to contain a
-colon-separated list of directories, which will be searched in order.
+command line. Then 'm4' looks in the current working directory. Next
+comes the directories specified with the '--include' or '-I' option, in
+the order found on the command line. Finally, if the 'M4PATH'
+environment variable is set, it is expected to contain a colon-separated
+list of directories, which will be searched in order.
- If the automatic search for include-files causes trouble, the `p'
+ If the automatic search for include-files causes trouble, the 'p'
debug flag (*note Debug Levels::) can help isolate the problem.
\1f
10 Diverting and undiverting output
***********************************
-Diversions are a way of temporarily saving output. The output of `m4'
+Diversions are a way of temporarily saving output. The output of 'm4'
can at any time be diverted to a temporary file, and be reinserted into
the output stream, "undiverted", again at a later time.
Numbered diversions are counted from 0 upwards, diversion number 0
-being the normal output stream. GNU `m4' tries to keep diversions in
+being the normal output stream. GNU 'm4' tries to keep diversions in
memory. However, there is a limit to the overall memory usable by all
-diversions taken together (512K, currently). When this maximum is
-about to be exceeded, a temporary file is opened to receive the
-contents of the biggest diversion still in memory, freeing this memory
-for other diversions. When creating the temporary file, `m4' honors
-the value of the environment variable `TMPDIR', and falls back to
-`/tmp'. Thus, the amount of available disk space provides the only
-real limit on the number and aggregate size of diversions.
+diversions taken together (512K, currently). When this maximum is about
+to be exceeded, a temporary file is opened to receive the contents of
+the biggest diversion still in memory, freeing this memory for other
+diversions. When creating the temporary file, 'm4' honors the value of
+the environment variable 'TMPDIR', and falls back to '/tmp'. Thus, the
+amount of available disk space provides the only real limit on the
+number and aggregate size of diversions.
Diversions make it possible to generate output in a different order
than the input was read. It is possible to implement topological
-sorting dependencies. For example, GNU Autoconf makes use of
-diversions under the hood to ensure that the expansion of a prerequisite
-macro appears in the output prior to the expansion of a dependent macro,
+sorting dependencies. For example, GNU Autoconf makes use of diversions
+under the hood to ensure that the expansion of a prerequisite macro
+appears in the output prior to the expansion of a dependent macro,
regardless of which order the two macros were invoked in the user's
input file.
10.1 Diverting output
=====================
-Output is diverted using `divert':
+Output is diverted using 'divert':
- -- Builtin: divert ([NUMBER = `0'])
+ -- Builtin: divert ([NUMBER = '0']
The current diversion is changed to NUMBER. If NUMBER is left out
or empty, it is assumed to be zero. If NUMBER cannot be parsed,
the diversion is unchanged.
- The expansion of `divert' is void.
+ The expansion of 'divert' is void.
- When all the `m4' input will have been processed, all existing
+ When all the 'm4' input will have been processed, all existing
diversions are automatically undiverted, in numerical order.
divert(`1')
=>
=>This text is diverted.
- Several calls of `divert' with the same argument do not overwrite
-the previous diverted text, but append to it. Diversions are printed
-after any wrapped text is expanded.
+ Several calls of 'divert' with the same argument do not overwrite the
+previous diverted text, but append to it. Diversions are printed after
+any wrapped text is expanded.
define(`text', `TEXT')
=>
If output is diverted to a negative diversion, it is simply
discarded. This can be used to suppress unwanted output. A common
example of unwanted output is the trailing newlines after macro
-definitions. Here is a common programming idiom in `m4' for avoiding
+definitions. Here is a common programming idiom in 'm4' for avoiding
them.
divert(`-1')
=>hello
=>world
- Note that `divert' is an English word, but also an active macro
+ Note that 'divert' is an English word, but also an active macro
without arguments. When processing plain text, the word might appear in
normal text and be unintentionally swallowed as a macro invocation. One
-way to avoid this is to use the `-P' option to rename all builtins
+way to avoid this is to use the '-P' option to rename all builtins
(*note Invoking m4: Operation modes.). Another is to write a wrapper
that requires a parameter to be recognized.
10.2 Undiverting output
=======================
-Diverted text can be undiverted explicitly using the builtin `undivert':
+Diverted text can be undiverted explicitly using the builtin 'undivert':
- -- Builtin: undivert ([DIVERSIONS...])
+ -- Builtin: undivert ([DIVERSIONS...]
Undiverts the numeric DIVERSIONS given by the arguments, in the
order given. If no arguments are supplied, all diversions are
undiverted, in numerical order.
without expansion. A warning is issued if a file could not be
opened.
- The expansion of `undivert' is void.
+ The expansion of 'undivert' is void.
divert(`1')
This text is diverted.
=>
Notice the last two blank lines. One of them comes from the newline
-following `undivert', the other from the newline that followed the
-`divert'! A diversion often starts with a blank line like this.
+following 'undivert', the other from the newline that followed the
+'divert'! A diversion often starts with a blank line like this.
- When diverted text is undiverted, it is _not_ reread by `m4', but
-rather copied directly to the current output, and it is therefore not
-an error to undivert into a diversion. Undiverting the empty string is
-the same as specifying diversion 0; in either case nothing happens
-since the output has already been flushed.
+ When diverted text is undiverted, it is _not_ reread by 'm4', but
+rather copied directly to the current output, and it is therefore not an
+error to undivert into a diversion. Undiverting the empty string is the
+same as specifying diversion 0; in either case nothing happens since the
+output has already been flushed.
divert(`1')diverted text
divert
=>one
=>three
- GNU `m4' allows named files to be undiverted. Given a non-numeric
+ GNU 'm4' allows named files to be undiverted. Given a non-numeric
argument, the contents of the file named will be copied, uninterpreted,
-to the current output. This complements the builtin `include' (*note
-Include::). To illustrate the difference, assume the file `foo'
+to the current output. This complements the builtin 'include' (*note
+Include::). To illustrate the difference, assume the file 'foo'
contains:
$ cat foo
=>
If the file is not found (or cannot be read), an error message is
-issued, and the expansion is void. It is possible to intermix files
-and diversion numbers.
+issued, and the expansion is void. It is possible to intermix files and
+diversion numbers.
divert(`1')diversion one
divert(`2')undivert(`foo')dnl
10.3 Diversion numbers
======================
-The current diversion is tracked by the builtin `divnum':
+The current diversion is tracked by the builtin 'divnum':
-- Builtin: divnum
Expands to the number of the current diversion.
text is actually needed. Since all non-empty diversion are brought back
on the main output stream when the end of input is seen, a method of
discarding a diversion is needed. If all diversions should be
-discarded, the easiest is to end the input to `m4' with `divert(`-1')'
-followed by an explicit `undivert':
+discarded, the easiest is to end the input to 'm4' with 'divert(`-1')'
+followed by an explicit 'undivert':
divert(`1')
Diversion one: divnum
Clearing selected diversions can be done with the following macro:
- -- Composite: cleardivert ([DIVERSIONS...])
+ -- Composite: cleardivert ([DIVERSIONS...]
Discard the contents of each of the listed numeric DIVERSIONS.
define(`cleardivert',
`pushdef(`_n', divnum)divert(`-1')undivert($@)divert(_n)popdef(`_n')')
=>
- It is called just like `undivert', but the effect is to clear the
+ It is called just like 'undivert', but the effect is to clear the
diversions, given by the arguments. (This macro has a nasty bug! You
should try to see if you can find it and correct it; or *note Answers:
Improved cleardivert.).
11 Macros for text handling
***************************
-There are a number of builtins in `m4' for manipulating text in various
+There are a number of builtins in 'm4' for manipulating text in various
ways, extracting substrings, searching, substituting, and so on.
* Menu:
11.1 Calculating length of strings
==================================
-The length of a string can be calculated by `len':
+The length of a string can be calculated by 'len':
-- Builtin: len (STRING)
Expands to the length of STRING, as a decimal number.
- The macro `len' is recognized only with parameters.
+ The macro 'len' is recognized only with parameters.
len()
=>0
11.2 Searching for substrings
=============================
-Searching for substrings is done with `index':
+Searching for substrings is done with 'index':
-- Builtin: index (STRING, SUBSTRING)
Expands to the index of the first occurrence of SUBSTRING in
STRING. The first character in STRING has index 0. If SUBSTRING
- does not occur in STRING, `index' expands to `-1'.
+ does not occur in STRING, 'index' expands to '-1'.
- The macro `index' is recognized only with parameters.
+ The macro 'index' is recognized only with parameters.
index(`gnus, gnats, and armadillos', `nat')
=>7
contrast this with an empty SUBSTRING.
index(`abc')
- error-->m4:stdin:1: Warning: too few arguments to builtin `index'
+ error->m4:stdin:1: Warning: too few arguments to builtin `index'
=>0
index(`abc', `')
=>0
11.3 Searching for regular expressions
======================================
-Searching for regular expressions is done with the builtin `regexp':
+Searching for regular expressions is done with the builtin 'regexp':
- -- Builtin: regexp (STRING, REGEXP, [REPLACEMENT])
+ -- Builtin: regexp (STRING, REGEXP, [REPLACEMENT]
Searches for REGEXP in STRING. The syntax for regular expressions
- is the same as in GNU Emacs, which is similar to BRE, Basic
- Regular Expressions in POSIX. *Note Syntax of Regular
- Expressions: (emacs)Regexps. Support for ERE, Extended Regular
- Expressions is not available, but will be added in GNU M4 2.0.
-
- If REPLACEMENT is omitted, `regexp' expands to the index of the
- first match of REGEXP in STRING. If REGEXP does not match
- anywhere in STRING, it expands to -1.
-
- If REPLACEMENT is supplied, and there was a match, `regexp'
- changes the expansion to this argument, with `\N' substituted by
- the text matched by the Nth parenthesized sub-expression of
- REGEXP, up to nine sub-expressions. The escape `\&' is replaced
- by the text of the entire regular expression matched. For all
- other characters, `\' treats the next character literally. A
- warning is issued if there were fewer sub-expressions than the
- `\N' requested, or if there is a trailing `\'. If there was no
- match, `regexp' expands to the empty string.
-
- The macro `regexp' is recognized only with parameters.
+ is the same as in GNU Emacs, which is similar to BRE, Basic Regular
+ Expressions in POSIX. *Note Syntax of Regular Expressions:
+ (emacs)Regexps. Support for ERE, Extended Regular Expressions is
+ not available, but will be added in GNU M4 2.0.
+
+ If REPLACEMENT is omitted, 'regexp' expands to the index of the
+ first match of REGEXP in STRING. If REGEXP does not match anywhere
+ in STRING, it expands to -1.
+
+ If REPLACEMENT is supplied, and there was a match, 'regexp' changes
+ the expansion to this argument, with '\N' substituted by the text
+ matched by the Nth parenthesized sub-expression of REGEXP, up to
+ nine sub-expressions. The escape '\&' is replaced by the text of
+ the entire regular expression matched. For all other characters,
+ '\' treats the next character literally. A warning is issued if
+ there were fewer sub-expressions than the '\N' requested, or if
+ there is a trailing '\'. If there was no match, 'regexp' expands
+ to the empty string.
+
+ The macro 'regexp' is recognized only with parameters.
regexp(`GNUs not Unix', `\<[a-z]\w+')
=>5
regexp(`abc', `\(b\)', `\\\10\a')
=>\b0a
regexp(`abc', `b', `\1\')
- error-->m4:stdin:2: Warning: sub-expression 1 not present
- error-->m4:stdin:2: Warning: trailing \ ignored in replacement
+ error->m4:stdin:2: Warning: sub-expression 1 not present
+ error->m4:stdin:2: Warning: trailing \ ignored in replacement
=>
regexp(`abc', `\(\(d\)?\)\(c\)', `\1\2\3\4\5\6')
- error-->m4:stdin:3: Warning: sub-expression 4 not present
- error-->m4:stdin:3: Warning: sub-expression 5 not present
- error-->m4:stdin:3: Warning: sub-expression 6 not present
+ error->m4:stdin:3: Warning: sub-expression 4 not present
+ error->m4:stdin:3: Warning: sub-expression 5 not present
+ error->m4:stdin:3: Warning: sub-expression 6 not present
=>c
- Omitting REGEXP evokes a warning, but still produces output;
-contrast this with an empty REGEXP argument.
+ Omitting REGEXP evokes a warning, but still produces output; contrast
+this with an empty REGEXP argument.
regexp(`abc')
- error-->m4:stdin:1: Warning: too few arguments to builtin `regexp'
+ error->m4:stdin:1: Warning: too few arguments to builtin `regexp'
=>0
regexp(`abc', `')
=>0
11.4 Extracting substrings
==========================
-Substrings are extracted with `substr':
+Substrings are extracted with 'substr':
- -- Builtin: substr (STRING, FROM, [LENGTH])
- Expands to the substring of STRING, which starts at index FROM,
- and extends for LENGTH characters, or to the end of STRING, if
- LENGTH is omitted. The starting index of a string is always 0.
- The expansion is empty if there is an error parsing FROM or
- LENGTH, if FROM is beyond the end of STRING, or if LENGTH is
- negative.
+ -- Builtin: substr (STRING, FROM, [LENGTH]
+ Expands to the substring of STRING, which starts at index FROM, and
+ extends for LENGTH characters, or to the end of STRING, if LENGTH
+ is omitted. The starting index of a string is always 0. The
+ expansion is empty if there is an error parsing FROM or LENGTH, if
+ FROM is beyond the end of STRING, or if LENGTH is negative.
- The macro `substr' is recognized only with parameters.
+ The macro 'substr' is recognized only with parameters.
substr(`gnus, gnats, and armadillos', `6')
=>gnats, and armadillos
Omitting FROM evokes a warning, but still produces output.
substr(`abc')
- error-->m4:stdin:1: Warning: too few arguments to builtin `substr'
+ error->m4:stdin:1: Warning: too few arguments to builtin `substr'
=>abc
substr(`abc',)
- error-->m4:stdin:2: empty string treated as 0 in builtin `substr'
+ error->m4:stdin:2: empty string treated as 0 in builtin `substr'
=>abc
\1f
11.5 Translating characters
===========================
-Character translation is done with `translit':
+Character translation is done with 'translit':
- -- Builtin: translit (STRING, CHARS, [REPLACEMENT])
+ -- Builtin: translit (STRING, CHARS, [REPLACEMENT]
Expands to STRING, with each character that occurs in CHARS
translated into the character from REPLACEMENT with the same index.
characters in REPLACEMENT also appear in CHARS.
As a GNU extension, both CHARS and REPLACEMENT can contain
- character-ranges, e.g., `a-z' (meaning all lowercase letters) or
- `0-9' (meaning all digits). To include a dash `-' in CHARS or
- REPLACEMENT, place it first or last in the entire string, or as
- the last character of a range. Back-to-back ranges can share a
- common endpoint. It is not an error for the last character in the
- range to be `larger' than the first. In that case, the range runs
- backwards, i.e., `9-0' means the string `9876543210'. The
+ character-ranges, e.g., 'a-z' (meaning all lowercase letters) or
+ '0-9' (meaning all digits). To include a dash '-' in CHARS or
+ REPLACEMENT, place it first or last in the entire string, or as the
+ last character of a range. Back-to-back ranges can share a common
+ endpoint. It is not an error for the last character in the range
+ to be 'larger' than the first. In that case, the range runs
+ backwards, i.e., '9-0' means the string '9876543210'. The
expansion of a range is dependent on the underlying encoding of
characters, so using ranges is not always portable between
machines.
- The macro `translit' is recognized only with parameters.
+ The macro 'translit' is recognized only with parameters.
translit(`GNUs not Unix', `A-Z')
=>s not nix
In the ASCII encoding, the first example deletes all uppercase
letters, the second converts lowercase to uppercase, and the third
-`mirrors' all uppercase letters, while converting them to lowercase.
+'mirrors' all uppercase letters, while converting them to lowercase.
The two first cases are by far the most common, even though they are not
-portable to EBCDIC or other encodings. The fourth example shows a
-range ending in `-', as well as back-to-back ranges. The final example
-shows that `a' is mapped to `b', not `c'; the resulting `b' is not
-further remapped to `g'; the `d' and `e' are swapped, and the `f' is
-discarded.
+portable to EBCDIC or other encodings. The fourth example shows a range
+ending in '-', as well as back-to-back ranges. The final example shows
+that 'a' is mapped to 'b', not 'c'; the resulting 'b' is not further
+remapped to 'g'; the 'd' and 'e' are swapped, and the 'f' is discarded.
Omitting CHARS evokes a warning, but still produces output.
translit(`abc')
- error-->m4:stdin:1: Warning: too few arguments to builtin `translit'
+ error->m4:stdin:1: Warning: too few arguments to builtin `translit'
=>abc
\1f
11.6 Substituting text by regular expression
============================================
-Global substitution in a string is done by `patsubst':
+Global substitution in a string is done by 'patsubst':
- -- Builtin: patsubst (STRING, REGEXP, [REPLACEMENT])
+ -- Builtin: patsubst (STRING, REGEXP, [REPLACEMENT]
Searches STRING for matches of REGEXP, and substitutes REPLACEMENT
for each match. The syntax for regular expressions is the same as
in GNU Emacs (*note Regexp::).
- The parts of STRING that are not covered by any match of REGEXP
- are copied to the expansion. Whenever a match is found, the
- search proceeds from the end of the match, so a character from
- STRING will never be substituted twice. If REGEXP matches a
- string of zero length, the start position for the search is
- incremented, to avoid infinite loops.
+ The parts of STRING that are not covered by any match of REGEXP are
+ copied to the expansion. Whenever a match is found, the search
+ proceeds from the end of the match, so a character from STRING will
+ never be substituted twice. If REGEXP matches a string of zero
+ length, the start position for the search is incremented, to avoid
+ infinite loops.
When a replacement is to be made, REPLACEMENT is inserted into the
- expansion, with `\N' substituted by the text matched by the Nth
+ expansion, with '\N' substituted by the text matched by the Nth
parenthesized sub-expression of PATSUBST, for up to nine
- sub-expressions. The escape `\&' is replaced by the text of the
- entire regular expression matched. For all other characters, `\'
+ sub-expressions. The escape '\&' is replaced by the text of the
+ entire regular expression matched. For all other characters, '\'
treats the next character literally. A warning is issued if there
- were fewer sub-expressions than the `\N' requested, or if there is
- a trailing `\'.
+ were fewer sub-expressions than the '\N' requested, or if there is
+ a trailing '\'.
The REPLACEMENT argument can be omitted, in which case the text
matched by REGEXP is deleted.
- The macro `patsubst' is recognized only with parameters.
+ The macro 'patsubst' is recognized only with parameters.
patsubst(`GNUs not Unix', `^', `OBS: ')
=>OBS: GNUs not Unix
patsubst(`GNUs not Unix', `[A-Z][a-z]+')
=>GN not
patsubst(`GNUs not Unix', `not', `NOT\')
- error-->m4:stdin:6: Warning: trailing \ ignored in replacement
+ error->m4:stdin:6: Warning: trailing \ ignored in replacement
=>GNUs NOT Unix
Here is a slightly more realistic example, which capitalizes
individual words or whole sentences, by substituting calls of the macros
-`upcase' and `downcase' into the strings.
+'upcase' and 'downcase' into the strings.
-- Composite: upcase (TEXT)
-- Composite: downcase (TEXT)
-- Composite: capitalize (TEXT)
- Expand to TEXT, but with capitalization changed: `upcase' changes
- all letters to upper case, `downcase' changes all letters to lower
- case, and `capitalize' changes the first character of each word to
+ Expand to TEXT, but with capitalization changed: 'upcase' changes
+ all letters to upper case, 'downcase' changes all letters to lower
+ case, and 'capitalize' changes the first character of each word to
upper case and the remaining characters to lower case.
First, an example of their usage, using implementations distributed
-in `m4-1.4.16/examples/capitalize.m4'.
+in 'm4-1.4.17/examples/capitalize.m4'.
$ m4 -I examples
include(`capitalize.m4')
capitalize(`GNUs not Unix')
=>Gnus Not Unix
- Now for the implementation. There is a helper macro `_capitalize'
-which puts only its first word in mixed case. Then `capitalize' merely
+ Now for the implementation. There is a helper macro '_capitalize'
+which puts only its first word in mixed case. Then 'capitalize' merely
parses out the words, and replaces them with an invocation of
-`_capitalize'. (As presented here, the `capitalize' macro has some
+'_capitalize'. (As presented here, the 'capitalize' macro has some
subtle flaws. You should try to see if you can find and correct them;
or *note Answers: Improved capitalize.).
=>define(`capitalize', `patsubst(`$1', `\w+', `_$0(`\&')')')
=>divert`'dnl
- While `regexp' replaces the whole input with the replacement as soon
-as there is a match, `patsubst' replaces each _occurrence_ of a match
+ While 'regexp' replaces the whole input with the replacement as soon
+as there is a match, 'patsubst' replaces each _occurrence_ of a match
and preserves non-matching pieces:
define(`patreg',
=>bab abb 212
=>bab
- Omitting REGEXP evokes a warning, but still produces output;
-contrast this with an empty REGEXP argument.
+ Omitting REGEXP evokes a warning, but still produces output; contrast
+this with an empty REGEXP argument.
patsubst(`abc')
- error-->m4:stdin:1: Warning: too few arguments to builtin `patsubst'
+ error->m4:stdin:1: Warning: too few arguments to builtin `patsubst'
=>abc
patsubst(`abc', `')
=>abc
11.7 Formatting strings (printf-like)
=====================================
-Formatted output can be made with `format':
+Formatted output can be made with 'format':
-- Builtin: format (FORMAT-STRING, ...)
- Works much like the C function `printf'. The first argument
- FORMAT-STRING can contain `%' specifications which are satisfied
- by additional arguments, and the expansion of `format' is the
+ Works much like the C function 'printf'. The first argument
+ FORMAT-STRING can contain '%' specifications which are satisfied by
+ additional arguments, and the expansion of 'format' is the
formatted string.
- The macro `format' is recognized only with parameters.
+ The macro 'format' is recognized only with parameters.
Its use is best described by a few examples:
format(`%g', `0xa.P+1')
=>20
- Using the `forloop' macro defined earlier (*note Forloop::), this
-example shows how `format' can be used to produce tabular output.
+ Using the 'forloop' macro defined earlier (*note Forloop::), this
+example shows how 'format' can be used to produce tabular output.
$ m4 -I examples
include(`forloop.m4')
=> 10 squared is 100
=>
- The builtin `format' is modeled after the ANSI C `printf' function,
-and supports these `%' specifiers: `c', `s', `d', `o', `x', `X', `u',
-`a', `A', `e', `E', `f', `F', `g', `G', and `%'; it supports field
-widths and precisions, and the flags `+', `-', ` ', `0', `#', and `''.
-For integer specifiers, the width modifiers `hh', `h', and `l' are
-recognized, and for floating point specifiers, the width modifier `l'
-is recognized. Items not yet supported include positional arguments,
-the `n', `p', `S', and `C' specifiers, the `z', `t', `j', `L' and `ll'
-modifiers, and any platform extensions available in the native
-`printf'. For more details on the functioning of `printf', see the C
-Library Manual, or the POSIX specification (for example, `%a' is
-supported even on platforms that haven't yet implemented C99
-hexadecimal floating point output natively).
+ The builtin 'format' is modeled after the ANSI C 'printf' function,
+and supports these '%' specifiers: 'c', 's', 'd', 'o', 'x', 'X', 'u',
+'a', 'A', 'e', 'E', 'f', 'F', 'g', 'G', and '%'; it supports field
+widths and precisions, and the flags '+', '-', ' ', '0', '#', and '''.
+For integer specifiers, the width modifiers 'hh', 'h', and 'l' are
+recognized, and for floating point specifiers, the width modifier 'l' is
+recognized. Items not yet supported include positional arguments, the
+'n', 'p', 'S', and 'C' specifiers, the 'z', 't', 'j', 'L' and 'll'
+modifiers, and any platform extensions available in the native 'printf'.
+For more details on the functioning of 'printf', see the C Library
+Manual, or the POSIX specification (for example, '%a' is supported even
+on platforms that haven't yet implemented C99 hexadecimal floating point
+output natively).
Unrecognized specifiers result in a warning. It is anticipated that
-a future release of GNU `m4' will support more specifiers, and give
+a future release of GNU 'm4' will support more specifiers, and give
better warnings when various problems such as overflow are encountered.
Likewise, escape sequences are not yet recognized.
format(`%p', `0')
- error-->m4:stdin:1: Warning: unrecognized specifier in `%p'
+ error->m4:stdin:1: Warning: unrecognized specifier in `%p'
=>
\1f
12 Macros for doing arithmetic
******************************
-Integer arithmetic is included in `m4', with a C-like syntax. As
+Integer arithmetic is included in 'm4', with a C-like syntax. As
convenient shorthands, there are builtins for simple increment and
decrement operations.
======================================
Increment and decrement of integers are supported using the builtins
-`incr' and `decr':
+'incr' and 'decr':
-- Builtin: incr (NUMBER)
-- Builtin: decr (NUMBER)
decremented, respectively, by one. Except for the empty string,
the expansion is empty if NUMBER could not be parsed.
- The macros `incr' and `decr' are recognized only with parameters.
+ The macros 'incr' and 'decr' are recognized only with parameters.
incr(`4')
=>5
decr(`7')
=>6
incr()
- error-->m4:stdin:3: empty string treated as 0 in builtin `incr'
+ error->m4:stdin:3: empty string treated as 0 in builtin `incr'
=>1
decr()
- error-->m4:stdin:4: empty string treated as 0 in builtin `decr'
+ error->m4:stdin:4: empty string treated as 0 in builtin `decr'
=>-1
\1f
12.2 Evaluating integer expressions
===================================
-Integer expressions are evaluated with `eval':
+Integer expressions are evaluated with 'eval':
- -- Builtin: eval (EXPRESSION, [RADIX = `10'], [WIDTH])
+ -- Builtin: eval (EXPRESSION, [RADIX = '10']
Expands to the value of EXPRESSION. The expansion is empty if a
problem is encountered while parsing the arguments. If specified,
RADIX and WIDTH control the format of the output.
Calculations are done with 32-bit signed numbers. Overflow
- silently results in wraparound. A warning is issued if division
- by zero is attempted, or if EXPRESSION could not be parsed.
+ silently results in wraparound. A warning is issued if division by
+ zero is attempted, or if EXPRESSION could not be parsed.
Expressions can contain the following operators, listed in order of
decreasing precedence.
- `()'
+ '()'
Parentheses
-
- `+ - ~ !'
+ '+ - ~ !'
Unary plus and minus, and bitwise and logical negation
-
- `**'
+ '**'
Exponentiation
-
- `* / %'
+ '* / %'
Multiplication, division, and modulo
-
- `+ -'
+ '+ -'
Addition and subtraction
-
- `<< >>'
+ '<< >>'
Shift left or right
-
- `> >= < <='
+ '> >= < <='
Relational operators
-
- `== !='
+ '== !='
Equality operators
-
- `&'
+ '&'
Bitwise and
-
- `^'
+ '^'
Bitwise exclusive-or
-
- `|'
+ '|'
Bitwise or
-
- `&&'
+ '&&'
Logical and
-
- `||'
+ '||'
Logical or
- The macro `eval' is recognized only with parameters.
+ The macro 'eval' is recognized only with parameters.
All binary operators, except exponentiation, are left associative. C
-operators that perform variable assignment, such as `+=' or `--', are
-not implemented, since `eval' only operates on constants, not
-variables. Attempting to use them results in an error. However, since
-traditional implementations treated `=' as an undocumented alias for
-`==' as opposed to an assignment operator, this usage is supported as a
-special case. Be aware that a future version of GNU M4 may support
-assignment semantics as an extension when POSIX mode is not requested,
-and that using `=' to check equality is not portable.
+operators that perform variable assignment, such as '+=' or '--', are
+not implemented, since 'eval' only operates on constants, not variables.
+Attempting to use them results in an error. However, since traditional
+implementations treated '=' as an undocumented alias for '==' as opposed
+to an assignment operator, this usage is supported as a special case.
+Be aware that a future version of GNU M4 may support assignment
+semantics as an extension when POSIX mode is not requested, and that
+using '=' to check equality is not portable.
eval(`2 = 2')
- error-->m4:stdin:1: Warning: recommend ==, not =, for equality operator
+ error->m4:stdin:1: Warning: recommend ==, not =, for equality operator
=>1
eval(`++0')
- error-->m4:stdin:2: invalid operator in eval: ++0
+ error->m4:stdin:2: invalid operator in eval: ++0
=>
eval(`0 |= 1')
- error-->m4:stdin:3: invalid operator in eval: 0 |= 1
+ error->m4:stdin:3: invalid operator in eval: 0 |= 1
=>
- Note that some older `m4' implementations use `^' as an alternate
+ Note that some older 'm4' implementations use '^' as an alternate
operator for the exponentiation, although POSIX requires the C behavior
-of bitwise exclusive-or. The precedence of the negation operators, `~'
-and `!', was traditionally lower than equality. The unary operators
+of bitwise exclusive-or. The precedence of the negation operators, '~'
+and '!', was traditionally lower than equality. The unary operators
could not be used reliably more than once on the same term without
intervening parentheses. The traditional precedence of the equality
-operators `==' and `!=' was identical instead of lower than the
-relational operators such as `<', even through GNU M4 1.4.8. Starting
-with version 1.4.9, GNU M4 correctly follows POSIX precedence rules.
-M4 scripts designed to be portable between releases must be aware that
+operators '==' and '!=' was identical instead of lower than the
+relational operators such as '<', even through GNU M4 1.4.8. Starting
+with version 1.4.9, GNU M4 correctly follows POSIX precedence rules. M4
+scripts designed to be portable between releases must be aware that
parentheses may be required to enforce C precedence rules. Likewise,
division by zero, even in the unused branch of a short-circuiting
operator, is not always well-defined in other implementations.
Following are some examples where the current version of M4 follows C
precedence rules, but where older versions and some other
-implementations of `m4' require explicit parentheses to get the correct
+implementations of 'm4' require explicit parentheses to get the correct
result:
eval(`1 == 2 > 0')
eval(`2 || 1 / 0')
=>1
eval(`0 || 1 / 0')
- error-->m4:stdin:9: divide by zero in eval: 0 || 1 / 0
+ error->m4:stdin:9: divide by zero in eval: 0 || 1 / 0
=>
eval(`0 && 1 % 0')
=>0
eval(`2 && 1 % 0')
- error-->m4:stdin:11: modulo by zero in eval: 2 && 1 % 0
+ error->m4:stdin:11: modulo by zero in eval: 2 && 1 % 0
=>
- As a GNU extension, the operator `**' performs integral
+ As a GNU extension, the operator '**' performs integral
exponentiation. The operator is right-associative, and if evaluated,
the exponent must be non-negative, and at least one of the arguments
must be non-zero, or a warning is issued.
=>1
eval(`0 ** 0')
=>
- error-->m4:stdin:5: divide by zero in eval: 0 ** 0
+ error->m4:stdin:5: divide by zero in eval: 0 ** 0
eval(`4 ** -2')
- error-->m4:stdin:6: negative exponent in eval: 4 ** -2
+ error->m4:stdin:6: negative exponent in eval: 4 ** -2
=>
Within EXPRESSION, (but not RADIX or WIDTH), numbers without a
-special prefix are decimal. A simple `0' prefix introduces an octal
-number. `0x' introduces a hexadecimal number. As GNU extensions, `0b'
-introduces a binary number. `0r' introduces a number expressed in any
-radix between 1 and 36: the prefix should be immediately followed by
-the decimal expression of the radix, a colon, then the digits making
-the number. For radix 1, leading zeros are ignored, and all remaining
-digits must be `1'; for all other radices, the digits are `0', `1', `2',
-.... Beyond `9', the digits are `a', `b' ... up to `z'. Lower and
+special prefix are decimal. A simple '0' prefix introduces an octal
+number. '0x' introduces a hexadecimal number. As GNU extensions, '0b'
+introduces a binary number. '0r' introduces a number expressed in any
+radix between 1 and 36: the prefix should be immediately followed by the
+decimal expression of the radix, a colon, then the digits making the
+number. For radix 1, leading zeros are ignored, and all remaining
+digits must be '1'; for all other radices, the digits are '0', '1', '2',
+.... Beyond '9', the digits are 'a', 'b' ... up to 'z'. Lower and
upper case letters can be used interchangeably in numbers prefixes and
as number digits.
- Parentheses may be used to group subexpressions whenever needed.
-For the relational operators, a true relation returns `1', and a false
-relation return `0'.
+ Parentheses may be used to group subexpressions whenever needed. For
+the relational operators, a true relation returns '1', and a false
+relation return '0'.
- Here are a few examples of use of `eval'.
+ Here are a few examples of use of 'eval'.
eval(`-3 * 5')
=>-15
define(`foo', `666')
=>
eval(`foo / 6')
- error-->m4:stdin:11: bad expression in eval: foo / 6
+ error->m4:stdin:11: bad expression in eval: foo / 6
=>
eval(foo / 6)
=>111
- As the last two lines show, `eval' does not handle macro names, even
+ As the last two lines show, 'eval' does not handle macro names, even
if they expand to a valid expression (or part of a valid expression).
-Therefore all macros must be expanded before they are passed to `eval'.
+Therefore all macros must be expanded before they are passed to 'eval'.
Some calculations are not portable to other implementations, since
-they have undefined semantics in C, but GNU `m4' has well-defined
+they have undefined semantics in C, but GNU 'm4' has well-defined
behavior on overflow. When shifting, an out-of-range shift amount is
implicitly brought into the range of 32-bit signed integers using an
implicit bit-wise and with 0x1f).
If RADIX is specified, it specifies the radix to be used in the
expansion. The default radix is 10; this is also the case if RADIX is
the empty string. A warning results if the radix is outside the range
-of 1 through 36, inclusive. The result of `eval' is always taken to be
-signed. No radix prefix is output, and for radices greater than 10,
-the digits are lower case. The WIDTH argument specifies the minimum
-output width, excluding any negative sign. The result is zero-padded
-to extend the expansion to the requested width. A warning results if
-the width is negative. If RADIX or WIDTH is out of bounds, the
-expansion of `eval' is empty.
+of 1 through 36, inclusive. The result of 'eval' is always taken to be
+signed. No radix prefix is output, and for radices greater than 10, the
+digits are lower case. The WIDTH argument specifies the minimum output
+width, excluding any negative sign. The result is zero-padded to extend
+the expansion to the requested width. A warning results if the width is
+negative. If RADIX or WIDTH is out of bounds, the expansion of 'eval'
+is empty.
eval(`666', `10')
=>666
eval(`10', `16')
=>a
eval(`1', `37')
- error-->m4:stdin:9: radix 37 in builtin `eval' out of range
+ error->m4:stdin:9: radix 37 in builtin `eval' out of range
=>
eval(`1', , `-1')
- error-->m4:stdin:10: negative width to builtin `eval'
+ error->m4:stdin:10: negative width to builtin `eval'
=>
eval()
- error-->m4:stdin:11: empty string treated as 0 in builtin `eval'
+ error->m4:stdin:11: empty string treated as 0 in builtin `eval'
=>0
\1f
13 Macros for running shell commands
************************************
-There are a few builtin macros in `m4' that allow you to run shell
-commands from within `m4'.
+There are a few builtin macros in 'm4' that allow you to run shell
+commands from within 'm4'.
Note that the definition of a valid shell command is system
-dependent. On UNIX systems, this is the typical `/bin/sh'. But on
+dependent. On UNIX systems, this is the typical '/bin/sh'. But on
other systems, such as native Windows, the shell has a different syntax
of commands that it understands. Some examples in this chapter assume
-`/bin/sh', and also demonstrate how to quit early with a known exit
+'/bin/sh', and also demonstrate how to quit early with a known exit
value if this is not the case.
* Menu:
13.1 Determining the platform
=============================
-Sometimes it is desirable for an input file to know which platform `m4'
-is running on. GNU `m4' provides several macros that are predefined to
+Sometimes it is desirable for an input file to know which platform 'm4'
+is running on. GNU 'm4' provides several macros that are predefined to
expand to the empty string; checking for their existence will confirm
platform details.
-- Optional builtin: unix
-- Optional builtin: __windows__
-- Optional builtin: windows
- Each of these macros is conditionally defined as needed to
- describe the environment of `m4'. If defined, each macro expands
- to the empty string. For now, these macros silently ignore all
- arguments, but in a future release of M4, they might warn if
- arguments are present.
+ Each of these macros is conditionally defined as needed to describe
+ the environment of 'm4'. If defined, each macro expands to the
+ empty string. For now, these macros silently ignore all arguments,
+ but in a future release of M4, they might warn if arguments are
+ present.
When GNU extensions are in effect (that is, when you did not use the
-`-G' option, *note Invoking m4: Limits control.), GNU `m4' will define
-the macro `__gnu__' to expand to the empty string.
+'-G' option, *note Invoking m4: Limits control.), GNU 'm4' will define
+the macro '__gnu__' to expand to the empty string.
$ m4
__gnu__
Extensions are ifdef(`__gnu__', `active', `inactive')
=>Extensions are inactive
- On UNIX systems, GNU `m4' will define `__unix__' by default, or
-`unix' when the `-G' option is specified.
+ On UNIX systems, GNU 'm4' will define '__unix__' by default, or
+'unix' when the '-G' option is specified.
- On native Windows systems, GNU `m4' will define `__windows__' by
-default, or `windows' when the `-G' option is specified.
+ On native Windows systems, GNU 'm4' will define '__windows__' by
+default, or 'windows' when the '-G' option is specified.
- On OS/2 systems, GNU `m4' will define `__os2__' by default, or `os2'
-when the `-G' option is specified.
+ On OS/2 systems, GNU 'm4' will define '__os2__' by default, or 'os2'
+when the '-G' option is specified.
- If GNU `m4' does not provide a platform macro for your system,
-please report that as a bug.
+ If GNU 'm4' does not provide a platform macro for your system, please
+report that as a bug.
define(`provided', `0')
=>
13.2 Executing simple commands
==============================
-Any shell command can be executed, using `syscmd':
+Any shell command can be executed, using 'syscmd':
-- Builtin: syscmd (SHELL-COMMAND)
Executes SHELL-COMMAND as a shell command.
- The expansion of `syscmd' is void, _not_ the output from
- SHELL-COMMAND! Output or error messages from SHELL-COMMAND are
- not read by `m4'. *Note Esyscmd::, if you need to process the
- command output.
+ The expansion of 'syscmd' is void, _not_ the output from
+ SHELL-COMMAND! Output or error messages from SHELL-COMMAND are not
+ read by 'm4'. *Note Esyscmd::, if you need to process the command
+ output.
- Prior to executing the command, `m4' flushes its buffers. The
+ Prior to executing the command, 'm4' flushes its buffers. The
default standard input, output and error of SHELL-COMMAND are the
- same as those of `m4'.
+ same as those of 'm4'.
By default, the SHELL-COMMAND will be used as the argument to the
- `-c' option of the `/bin/sh' shell (or the version of `sh'
- specified by `command -p getconf PATH', if your system supports
- that). If you prefer a different shell, the `configure' script
- can be given the option `--with-syscmd-shell=LOCATION' to set the
- location of an alternative shell at GNU `m4' installation; the
- alternative shell must still support `-c'.
+ '-c' option of the '/bin/sh' shell (or the version of 'sh'
+ specified by 'command -p getconf PATH', if your system supports
+ that). If you prefer a different shell, the 'configure' script can
+ be given the option '--with-syscmd-shell=LOCATION' to set the
+ location of an alternative shell at GNU 'm4' installation; the
+ alternative shell must still support '-c'.
- The macro `syscmd' is recognized only with parameters.
+ The macro 'syscmd' is recognized only with parameters.
define(`foo', `FOO')
=>
=>foo
=>
- Note how the expansion of `syscmd' keeps the trailing newline of the
+ Note how the expansion of 'syscmd' keeps the trailing newline of the
command, as well as using the newline that appeared after the macro.
The following is an example of SHELL-COMMAND using the same standard
-input as `m4':
+input as 'm4':
$ echo "m4wrap(\`syscmd(\`cat')')" | m4
=>
- It tells `m4' to read all of its input before executing the wrapped
+ It tells 'm4' to read all of its input before executing the wrapped
text, then hand a valid (albeit emptied) pipe as standard input for the
-`cat' subcommand. Therefore, you should be careful when using standard
-input (either by specifying no files, or by passing `-' as a file name
+'cat' subcommand. Therefore, you should be careful when using standard
+input (either by specifying no files, or by passing '-' as a file name
on the command line, *note Invoking m4: Command line files.), and also
-invoking subcommands via `syscmd' or `esyscmd' that consume data from
+invoking subcommands via 'syscmd' or 'esyscmd' that consume data from
standard input. When standard input is a seekable file, the subprocess
-will pick up with the next character not yet processed by `m4'; when it
+will pick up with the next character not yet processed by 'm4'; when it
is a pipe or other non-seekable file, there is no guarantee how much
-data will already be buffered by `m4' and thus unavailable to the child.
+data will already be buffered by 'm4' and thus unavailable to the child.
\1f
File: m4.info, Node: Esyscmd, Next: Sysval, Prev: Syscmd, Up: Shell commands
13.3 Reading the output of commands
===================================
-If you want `m4' to read the output of a shell command, use `esyscmd':
+If you want 'm4' to read the output of a shell command, use 'esyscmd':
-- Builtin: esyscmd (SHELL-COMMAND)
Expands to the standard output of the shell command SHELL-COMMAND.
- Prior to executing the command, `m4' flushes its buffers. The
+ Prior to executing the command, 'm4' flushes its buffers. The
default standard input and standard error of SHELL-COMMAND are the
- same as those of `m4'. The error output of SHELL-COMMAND is not a
+ same as those of 'm4'. The error output of SHELL-COMMAND is not a
part of the expansion: it will appear along with the error output
- of `m4'.
+ of 'm4'.
By default, the SHELL-COMMAND will be used as the argument to the
- `-c' option of the `/bin/sh' shell (or the version of `sh'
- specified by `command -p getconf PATH', if your system supports
- that). If you prefer a different shell, the `configure' script
- can be given the option `--with-syscmd-shell=LOCATION' to set the
- location of an alternative shell at GNU `m4' installation; the
- alternative shell must still support `-c'.
+ '-c' option of the '/bin/sh' shell (or the version of 'sh'
+ specified by 'command -p getconf PATH', if your system supports
+ that). If you prefer a different shell, the 'configure' script can
+ be given the option '--with-syscmd-shell=LOCATION' to set the
+ location of an alternative shell at GNU 'm4' installation; the
+ alternative shell must still support '-c'.
- The macro `esyscmd' is recognized only with parameters.
+ The macro 'esyscmd' is recognized only with parameters.
define(`foo', `FOO')
=>
=>FOO
=>
- Note how the expansion of `esyscmd' keeps the trailing newline of
-the command, as well as using the newline that appeared after the macro.
+ Note how the expansion of 'esyscmd' keeps the trailing newline of the
+command, as well as using the newline that appeared after the macro.
- Just as with `syscmd', care must be exercised when sharing standard
-input between `m4' and the child process of `esyscmd'.
+ Just as with 'syscmd', care must be exercised when sharing standard
+input between 'm4' and the child process of 'esyscmd'.
\1f
File: m4.info, Node: Sysval, Next: Mkstemp, Prev: Esyscmd, Up: Shell commands
13.4 Exit status
================
-To see whether a shell command succeeded, use `sysval':
+To see whether a shell command succeeded, use 'sysval':
-- Builtin: sysval
Expands to the exit status of the last shell command run with
- `syscmd' or `esyscmd'. Expands to 0 if no command has been run
+ 'syscmd' or 'esyscmd'. Expands to 0 if no command has been run
yet.
sysval
sysval
=>0
- `sysval' results in 127 if there was a problem executing the
-command, for example, if the system-imposed argument length is exceeded,
-or if there were not enough resources to fork. It is not possible to
+ 'sysval' results in 127 if there was a problem executing the command,
+for example, if the system-imposed argument length is exceeded, or if
+there were not enough resources to fork. It is not possible to
distinguish between failed execution and successful execution that had
an exit status of 127, unless there was output from the child process.
13.5 Making temporary files
===========================
-Commands specified to `syscmd' or `esyscmd' might need a temporary
-file, for output or for some other purpose. There is a builtin macro,
-`mkstemp', for making a temporary file:
+Commands specified to 'syscmd' or 'esyscmd' might need a temporary file,
+for output or for some other purpose. There is a builtin macro,
+'mkstemp', for making a temporary file:
-- Builtin: mkstemp (TEMPLATE)
-- Builtin: maketemp (TEMPLATE)
Expands to the quoted name of a new, empty file, made from the
- string TEMPLATE, which should end with the string `XXXXXX'. The
- six `X' characters are then replaced with random characters
- matching the regular expression `[a-zA-Z0-9._-]', in order to make
- the file name unique. If fewer than six `X' characters are found
- at the end of `template', the result will be longer than the
+ string TEMPLATE, which should end with the string 'XXXXXX'. The
+ six 'X' characters are then replaced with random characters
+ matching the regular expression '[a-zA-Z0-9._-]', in order to make
+ the file name unique. If fewer than six 'X' characters are found
+ at the end of 'template', the result will be longer than the
template. The created file will have access permissions as if by
- `chmod =rw,go=', meaning that the current umask of the `m4'
- process is taken into account, and at most only the current user
- can read and write the file.
-
- The traditional behavior, standardized by POSIX, is that
- `maketemp' merely replaces the trailing `X' with the process id,
- without creating a file or quoting the expansion, and without
- ensuring that the resulting string is a unique file name. In
- part, this means that using the same TEMPLATE twice in the same
- input file will result in the same expansion. This behavior is a
- security hole, as it is very easy for another process to guess the
- name that will be generated, and thus interfere with a subsequent
- use of `syscmd' trying to manipulate that file name. Hence, POSIX
- has recommended that all new implementations of `m4' provide the
- secure `mkstemp' builtin, and that users of `m4' check for its
- existence.
+ 'chmod =rw,go=', meaning that the current umask of the 'm4' process
+ is taken into account, and at most only the current user can read
+ and write the file.
+
+ The traditional behavior, standardized by POSIX, is that 'maketemp'
+ merely replaces the trailing 'X' with the process id, without
+ creating a file or quoting the expansion, and without ensuring that
+ the resulting string is a unique file name. In part, this means
+ that using the same TEMPLATE twice in the same input file will
+ result in the same expansion. This behavior is a security hole, as
+ it is very easy for another process to guess the name that will be
+ generated, and thus interfere with a subsequent use of 'syscmd'
+ trying to manipulate that file name. Hence, POSIX has recommended
+ that all new implementations of 'm4' provide the secure 'mkstemp'
+ builtin, and that users of 'm4' check for its existence.
The expansion is void and an error issued if a temporary file could
not be created.
- The macros `mkstemp' and `maketemp' are recognized only with
+ The macros 'mkstemp' and 'maketemp' are recognized only with
parameters.
If you try this next example, you will most likely get different
mkstemp(`doc')
=>docQv83Uw
- Unless you use the `--traditional' command line option (or `-G',
-*note Invoking m4: Limits control.), the GNU version of `maketemp' is
+ Unless you use the '--traditional' command line option (or '-G',
+*note Invoking m4: Limits control.), the GNU version of 'maketemp' is
secure. This means that using the same template to multiple calls will
generate multiple files. However, we recommend that you use the new
-`mkstemp' macro, introduced in GNU M4 1.4.8, which is secure even in
+'mkstemp' macro, introduced in GNU M4 1.4.8, which is secure even in
traditional mode. Also, as of M4 1.4.11, the secure implementation
quotes the resulting file name, so that you are guaranteed to know what
file was created even if the random file name happens to match an
-existing macro. Notice that this example is careful to use `defn' to
-avoid unintended expansion of `foo'.
+existing macro. Notice that this example is careful to use 'defn' to
+avoid unintended expansion of 'foo'.
$ m4
define(`foo', `errprint(`oops')')
* Errprint:: Printing error messages
* Location:: Printing current location
-* M4exit:: Exiting from `m4'
+* M4exit:: Exiting from 'm4'
\1f
File: m4.info, Node: Errprint, Next: Location, Up: Miscellaneous
14.1 Printing error messages
============================
-You can print error messages using `errprint':
+You can print error messages using 'errprint':
-- Builtin: errprint (MESSAGE, ...)
Prints MESSAGE and the rest of the arguments to standard error,
separated by spaces. Standard error is used, regardless of the
- `--debugfile' option (*note Invoking m4: Debugging options.).
+ '--debugfile' option (*note Invoking m4: Debugging options.).
- The expansion of `errprint' is void. The macro `errprint' is
+ The expansion of 'errprint' is void. The macro 'errprint' is
recognized only with parameters.
errprint(`Invalid arguments to forloop
')
- error-->Invalid arguments to forloop
+ error->Invalid arguments to forloop
=>
errprint(`1')errprint(`2',`3
')
- error-->12 3
+ error->12 3
=>
A trailing newline is _not_ printed automatically, so it should be
supplied as part of the argument, as in the example. Unfortunately, the
-exact output of `errprint' is not very portable to other `m4'
+exact output of 'errprint' is not very portable to other 'm4'
implementations: POSIX requires that all arguments be printed, but some
-implementations of `m4' only print the first. Furthermore, some BSD
-implementations always append a newline for each `errprint' call,
+implementations of 'm4' only print the first. Furthermore, some BSD
+implementations always append a newline for each 'errprint' call,
regardless of whether the last argument already had one, and POSIX is
silent on whether this is acceptable.
-- Builtin: __program__
Expand to the quoted name of the current input file, the current
input line number in that file, and the quoted name of the current
- invocation of `m4'.
+ invocation of 'm4'.
errprint(__program__:__file__:__line__: `input error
')
- error-->m4:stdin:1: input error
+ error->m4:stdin:1: input error
=>
Line numbers start at 1 for each file. If the file was found due to
-the `-I' option or `M4PATH' environment variable, that is reflected in
-the file name. The syncline option (`-s', *note Invoking m4:
-Preprocessor features.), and the `f' and `l' flags of `debugmode'
-(*note Debug Levels::), also use this notion of current file and line.
+the '-I' option or 'M4PATH' environment variable, that is reflected in
+the file name. The syncline option ('-s', *note Invoking m4:
+Preprocessor features.), and the 'f' and 'l' flags of 'debugmode' (*note
+Debug Levels::), also use this notion of current file and line.
Redefining the three location macros has no effect on syncline, debug,
warning, or error message output.
- This example reuses the file `incl.m4' mentioned earlier (*note
+ This example reuses the file 'incl.m4' mentioned earlier (*note
Include::):
$ m4 -I examples
expansion text corresponds to the location in the file where the
expansion was triggered, regardless of how many newline characters the
expansion text contains. As of GNU M4 1.4.8, the location of text
-wrapped with `m4wrap' (*note M4wrap::) is the point at which the
-`m4wrap' was invoked. Previous versions, however, behaved as though
+wrapped with 'm4wrap' (*note M4wrap::) is the point at which the
+'m4wrap' was invoked. Previous versions, however, behaved as though
wrapped text came from line 0 of the file "".
define(`echo', `$@')
foo(errprint(__line__
__line__
))
- error-->8
- error-->9
+ error->8
+ error->9
=>8
=>8
__line__
=>6
=>6
- The `__program__' macro behaves like `$0' in shell terminology. If
-you invoke `m4' through an absolute path or a link with a different
-spelling, rather than by relying on a `PATH' search for plain `m4', it
-will affect how `__program__' expands. The intent is that you can use
-it to produce error messages with the same formatting that `m4'
-produces internally. It can also be used within `syscmd' (*note
-Syscmd::) to pick the same version of `m4' that is currently running,
-rather than whatever version of `m4' happens to be first in `PATH'. It
-was first introduced in GNU M4 1.4.6.
+ The '__program__' macro behaves like '$0' in shell terminology. If
+you invoke 'm4' through an absolute path or a link with a different
+spelling, rather than by relying on a 'PATH' search for plain 'm4', it
+will affect how '__program__' expands. The intent is that you can use
+it to produce error messages with the same formatting that 'm4' produces
+internally. It can also be used within 'syscmd' (*note Syscmd::) to
+pick the same version of 'm4' that is currently running, rather than
+whatever version of 'm4' happens to be first in 'PATH'. It was first
+introduced in GNU M4 1.4.6.
\1f
File: m4.info, Node: M4exit, Prev: Location, Up: Miscellaneous
-14.3 Exiting from `m4'
+14.3 Exiting from 'm4'
======================
-If you need to exit from `m4' before the entire input has been read,
-you can use `m4exit':
+If you need to exit from 'm4' before the entire input has been read, you
+can use 'm4exit':
- -- Builtin: m4exit ([CODE = `0'])
- Causes `m4' to exit, with exit status CODE. If CODE is left out,
+ -- Builtin: m4exit ([CODE = '0']
+ Causes 'm4' to exit, with exit status CODE. If CODE is left out,
the exit status is zero. If CODE cannot be parsed, or is outside
- the range of 0 to 255, the exit status is one. No further input
- is read, and all wrapped and diverted text is discarded.
+ the range of 0 to 255, the exit status is one. No further input is
+ read, and all wrapped and diverted text is discarded.
m4wrap(`This text is lost due to `m4exit'.')
=>
')m4exit(`1')')
=>
fatal_error(`this is a BAD one, buster')
- error-->m4:stdin:4: fatal error: this is a BAD one, buster
+ error->m4:stdin:4: fatal error: this is a BAD one, buster
- After this macro call, `m4' will exit with exit status 1. This macro
+ After this macro call, 'm4' will exit with exit status 1. This macro
is only intended for error exits, since the normal exit procedures are
not followed, i.e., diverted text is not undiverted, and saved text
(*note M4wrap::) is not reread. (This macro could be made more robust
-to earlier versions of `m4'. You should try to see if you can find
+to earlier versions of 'm4'. You should try to see if you can find
weaknesses and correct them; or *note Answers: Improved fatal_error.).
Note that it is still possible for the exit status to be different
-than what was requested by `m4exit'. If `m4' detects some other error,
+than what was requested by 'm4exit'. If 'm4' detects some other error,
such as a write error on standard output, the exit status will be
-non-zero even if `m4exit' requested zero.
+non-zero even if 'm4exit' requested zero.
If standard input is seekable, then the file will be positioned at
the next unread character. If it is a pipe or other non-seekable file,
-then there are no guarantees how much data `m4' might have read into
+then there are no guarantees how much data 'm4' might have read into
buffers, and thus discarded.
\1f
15 Fast loading of frozen state
*******************************
-Some bigger `m4' applications may be built over a common base
-containing hundreds of definitions and other costly initializations.
-Usually, the common base is kept in one or more declarative files,
-which files are listed on each `m4' invocation prior to the user's
-input file, or else each input file uses `include'.
+Some bigger 'm4' applications may be built over a common base containing
+hundreds of definitions and other costly initializations. Usually, the
+common base is kept in one or more declarative files, which files are
+listed on each 'm4' invocation prior to the user's input file, or else
+each input file uses 'include'.
Reading the common base of a big application, over and over again,
-may be time consuming. GNU `m4' offers some machinery to speed up the
+may be time consuming. GNU 'm4' offers some machinery to speed up the
start of an application using lengthy common bases.
* Menu:
15.1 Using frozen files
=======================
-Suppose a user has a library of `m4' initializations in `base.m4',
-which is then used with multiple input files:
+Suppose a user has a library of 'm4' initializations in 'base.m4', which
+is then used with multiple input files:
$ m4 base.m4 input1.m4
$ m4 base.m4 input2.m4
$ m4 base.m4 input3.m4
- Rather than spending time parsing the fixed contents of `base.m4'
+ Rather than spending time parsing the fixed contents of 'base.m4'
every time, the user might rather execute:
$ m4 -F base.m4f base.m4
$ m4 -R base.m4f input2.m4
$ m4 -R base.m4f input3.m4
-with the varying input. The first call, containing the `-F' option,
-only reads and executes file `base.m4', defining various application
+with the varying input. The first call, containing the '-F' option,
+only reads and executes file 'base.m4', defining various application
macros and computing other initializations. Once the input file
-`base.m4' has been completely processed, GNU `m4' produces in
-`base.m4f' a "frozen" file, that is, a file which contains a kind of
-snapshot of the `m4' internal state.
-
- Later calls, containing the `-R' option, are able to reload the
-internal state of `m4', from `base.m4f', _prior_ to reading any other
-input files. This means instead of starting with a virgin copy of
-`m4', input will be read after having effectively recovered the effect
-of a prior run. In our example, the effect is the same as if file
-`base.m4' has been read anew. However, this effect is achieved a lot
-faster.
-
- Only one frozen file may be created or read in any one `m4'
+'base.m4' has been completely processed, GNU 'm4' produces in 'base.m4f'
+a "frozen" file, that is, a file which contains a kind of snapshot of
+the 'm4' internal state.
+
+ Later calls, containing the '-R' option, are able to reload the
+internal state of 'm4', from 'base.m4f', _prior_ to reading any other
+input files. This means instead of starting with a virgin copy of 'm4',
+input will be read after having effectively recovered the effect of a
+prior run. In our example, the effect is the same as if file 'base.m4'
+has been read anew. However, this effect is achieved a lot faster.
+
+ Only one frozen file may be created or read in any one 'm4'
invocation. It is not possible to recover two frozen files at once.
-However, frozen files may be updated incrementally, through using `-R'
-and `-F' options simultaneously. For example, if some care is taken,
+However, frozen files may be updated incrementally, through using '-R'
+and '-F' options simultaneously. For example, if some care is taken,
the command:
$ m4 file1.m4 file2.m4 file3.m4 file4.m4
$ m4 -R file3.m4f file4.m4
Some care is necessary because not every effort has been made for
-this to work in all cases. In particular, the trace attribute of
-macros is not handled, nor the current setting of `changeword'.
-Currently, `m4wrap' and `sysval' also have problems. Also,
-interactions for some options of `m4', being used in one call and not
-in the next, have not been fully analyzed yet. On the other end, you
-may be confident that stacks of `pushdef' definitions are handled
-correctly, as well as undefined or renamed builtins, and changed
-strings for quotes or comments. And future releases of GNU M4 will
-improve on the utility of frozen files.
-
- When an `m4' run is to be frozen, the automatic undiversion which
+this to work in all cases. In particular, the trace attribute of macros
+is not handled, nor the current setting of 'changeword'. Currently,
+'m4wrap' and 'sysval' also have problems. Also, interactions for some
+options of 'm4', being used in one call and not in the next, have not
+been fully analyzed yet. On the other end, you may be confident that
+stacks of 'pushdef' definitions are handled correctly, as well as
+undefined or renamed builtins, and changed strings for quotes or
+comments. And future releases of GNU M4 will improve on the utility of
+frozen files.
+
+ When an 'm4' run is to be frozen, the automatic undiversion which
takes place at end of execution is inhibited. Instead, all positively
numbered diversions are saved into the frozen file. The active
diversion number is also transmitted.
A frozen file to be reloaded need not reside in the current
-directory. It is looked up the same way as an `include' file (*note
+directory. It is looked up the same way as an 'include' file (*note
Search Path::).
- If the frozen file was generated with a newer version of `m4', and
-contains directives that an older `m4' cannot parse, attempting to load
-the frozen file with option `-R' will cause `m4' to exit with status 63
+ If the frozen file was generated with a newer version of 'm4', and
+contains directives that an older 'm4' cannot parse, attempting to load
+the frozen file with option '-R' will cause 'm4' to exit with status 63
to indicate version mismatch.
\1f
=======================
Frozen files are sharable across architectures. It is safe to write a
-frozen file on one machine and read it on another, given that the
-second machine uses the same or newer version of GNU `m4'. It is
-conventional, but not required, to give a frozen file the suffix of
-`.m4f'.
+frozen file on one machine and read it on another, given that the second
+machine uses the same or newer version of GNU 'm4'. It is conventional,
+but not required, to give a frozen file the suffix of '.m4f'.
These are simple (editable) text files, made up of directives, each
starting with a capital letter and ending with a newline (<NL>).
-Wherever a directive is expected, the character `#' introduces a
-comment line; empty lines are also ignored if they are not part of an
-embedded string. In the following descriptions, each LEN refers to the
-length of the corresponding strings STR in the next line of input.
-Numbers are always expressed in decimal. There are no escape
-characters. The directives are:
-
-`C LEN1 , LEN2 <NL> STR1 STR2 <NL>'
+Wherever a directive is expected, the character '#' introduces a comment
+line; empty lines are also ignored if they are not part of an embedded
+string. In the following descriptions, each LEN refers to the length of
+the corresponding strings STR in the next line of input. Numbers are
+always expressed in decimal. There are no escape characters. The
+directives are:
+
+'C LEN1 , LEN2 <NL> STR1 STR2 <NL>'
Uses STR1 and STR2 as the begin-comment and end-comment strings.
- If omitted, then `#' and <NL> are the comment delimiters.
+ If omitted, then '#' and <NL> are the comment delimiters.
-`D NUMBER, LEN <NL> STR <NL>'
+'D NUMBER, LEN <NL> STR <NL>'
Selects diversion NUMBER, making it current, then copy STR in the
current diversion. NUMBER may be a negative number for a
- non-existing diversion. To merely specify an active selection,
- use this command with an empty STR. With 0 as the diversion
- NUMBER, STR will be issued on standard output at reload time. GNU
- `m4' will not produce the `D' directive with non-zero length for
+ non-existing diversion. To merely specify an active selection, use
+ this command with an empty STR. With 0 as the diversion NUMBER,
+ STR will be issued on standard output at reload time. GNU 'm4'
+ will not produce the 'D' directive with non-zero length for
diversion 0, but this can be done with manual edits. This
directive may appear more than once for the same diversion, in
which case the diversion is the concatenation of the various uses.
If omitted, then diversion 0 is current.
-`F LEN1 , LEN2 <NL> STR1 STR2 <NL>'
- Defines, through `pushdef', a definition for STR1 expanding to the
- function whose builtin name is STR2. If the builtin does not
- exist (for example, if the frozen file was produced by a copy of
- `m4' compiled with changeword support, but the version of `m4'
- reloading was compiled without it), the reload is silent, but any
- subsequent use of the definition of STR1 will result in a warning.
- This directive may appear more than once for the same name, and
- its order, along with `T', is important. If omitted, you will
- have no access to any builtins.
-
-`Q LEN1 , LEN2 <NL> STR1 STR2 <NL>'
+'F LEN1 , LEN2 <NL> STR1 STR2 <NL>'
+ Defines, through 'pushdef', a definition for STR1 expanding to the
+ function whose builtin name is STR2. If the builtin does not exist
+ (for example, if the frozen file was produced by a copy of 'm4'
+ compiled with changeword support, but the version of 'm4' reloading
+ was compiled without it), the reload is silent, but any subsequent
+ use of the definition of STR1 will result in a warning. This
+ directive may appear more than once for the same name, and its
+ order, along with 'T', is important. If omitted, you will have no
+ access to any builtins.
+
+'Q LEN1 , LEN2 <NL> STR1 STR2 <NL>'
Uses STR1 and STR2 as the begin-quote and end-quote strings. If
- omitted, then ``' and `'' are the quote delimiters.
+ omitted, then '`' and ''' are the quote delimiters.
-`T LEN1 , LEN2 <NL> STR1 STR2 <NL>'
- Defines, though `pushdef', a definition for STR1 expanding to the
+'T LEN1 , LEN2 <NL> STR1 STR2 <NL>'
+ Defines, though 'pushdef', a definition for STR1 expanding to the
text given by STR2. This directive may appear more than once for
- the same name, and its order, along with `F', is important.
+ the same name, and its order, along with 'F', is important.
-`V NUMBER <NL>'
- Confirms the format of the file. `m4' 1.4.16 only creates and
- understands frozen files where NUMBER is 1. This directive must
- be the first non-comment in the file, and may not appear more than
+'V NUMBER <NL>'
+ Confirms the format of the file. 'm4' 1.4.17 only creates and
+ understands frozen files where NUMBER is 1. This directive must be
+ the first non-comment in the file, and may not appear more than
once.
\1f
File: m4.info, Node: Compatibility, Next: Answers, Prev: Frozen files, Up: Top
-16 Compatibility with other versions of `m4'
+16 Compatibility with other versions of 'm4'
********************************************
This chapter describes the many of the differences between this
-implementation of `m4', and of other implementations found under UNIX,
-such as System V Release 3, Solaris, and BSD flavors. In particular,
-it lists the known differences and extensions to POSIX. However, the
-list is not necessarily comprehensive.
+implementation of 'm4', and of other implementations found under UNIX,
+such as System V Release 4, Solaris, and BSD flavors. In particular, it
+lists the known differences and extensions to POSIX. However, the list
+is not necessarily comprehensive.
At the time of this writing, POSIX 2001 (also known as IEEE Std
1003.1-2001) is the latest standard, although a new version of POSIX is
-under development and includes several proposals for modifying what
-`m4' is required to do. The requirements for `m4' are shared between
-SUSv3 and POSIX, and can be viewed at
-`http://www.opengroup.org/onlinepubs/000095399/utilities/m4.html'.
+under development and includes several proposals for modifying what 'm4'
+is required to do. The requirements for 'm4' are shared between SUSv3
+and POSIX, and can be viewed at
+<http://www.opengroup.org/onlinepubs/000095399/utilities/m4.html>.
* Menu:
16.1 Extensions in GNU M4
=========================
-This version of `m4' contains a few facilities that do not exist in
-System V `m4'. These extra facilities are all suppressed by using the
-`-G' command line option (*note Invoking m4: Limits control.), unless
+This version of 'm4' contains a few facilities that do not exist in
+System V 'm4'. These extra facilities are all suppressed by using the
+'-G' command line option (*note Invoking m4: Limits control.), unless
overridden by other command line options.
- * In the `$N' notation for macro arguments, N can contain several
- digits, while the System V `m4' only accepts one digit. This
- allows macros in GNU `m4' to take any number of arguments, and not
+ * In the '$N' notation for macro arguments, N can contain several
+ digits, while the System V 'm4' only accepts one digit. This
+ allows macros in GNU 'm4' to take any number of arguments, and not
only nine (*note Arguments::).
- This means that `define(`foo', `$11')' is ambiguous between
+ This means that 'define(`foo', `$11')' is ambiguous between
implementations. To portably choose between grabbing the first
parameter and appending 1 to the expansion, or grabbing the
eleventh parameter, you can do the following:
Eleventh(`a', `b', `c', `d', `e', `f', `g', `h', `i', `j', `k')
=>k
- Also see the `argn' macro (*note Shift::).
+ Also see the 'argn' macro (*note Shift::).
- * The `divert' (*note Divert::) macro can manage more than 9
- diversions. GNU `m4' treats all positive numbers as valid
+ * The 'divert' (*note Divert::) macro can manage more than 9
+ diversions. GNU 'm4' treats all positive numbers as valid
diversions, rather than discarding diversions greater than 9.
- * Files included with `include' and `sinclude' are sought in a user
+ * Files included with 'include' and 'sinclude' are sought in a user
specified search path, if they are not found in the working
- directory. The search path is specified by the `-I' option and the
- `M4PATH' environment variable (*note Search Path::).
+ directory. The search path is specified by the '-I' option and the
+ 'M4PATH' environment variable (*note Search Path::).
- * Arguments to `undivert' can be non-numeric, in which case the named
+ * Arguments to 'undivert' can be non-numeric, in which case the named
file will be included uninterpreted in the output (*note
Undivert::).
- * Formatted output is supported through the `format' builtin, which
- is modeled after the C library function `printf' (*note Format::).
+ * Formatted output is supported through the 'format' builtin, which
+ is modeled after the C library function 'printf' (*note Format::).
* Searches and text substitution through basic regular expressions
- are supported by the `regexp' (*note Regexp::) and `patsubst'
- (*note Patsubst::) builtins. Some BSD implementations use
- extended regular expressions instead.
+ are supported by the 'regexp' (*note Regexp::) and 'patsubst'
+ (*note Patsubst::) builtins. Some BSD implementations use extended
+ regular expressions instead.
- * The output of shell commands can be read into `m4' with `esyscmd'
+ * The output of shell commands can be read into 'm4' with 'esyscmd'
(*note Esyscmd::).
- * There is indirect access to any builtin macro with `builtin'
- (*note Builtin::).
+ * There is indirect access to any builtin macro with 'builtin' (*note
+ Builtin::).
- * Macros can be called indirectly through `indir' (*note Indir::).
+ * Macros can be called indirectly through 'indir' (*note Indir::).
* The name of the program, the current input file, and the current
input line number are accessible through the builtins
- `__program__', `__file__', and `__line__' (*note Location::).
+ '__program__', '__file__', and '__line__' (*note Location::).
- * The format of the output from `dumpdef' and macro tracing can be
- controlled with `debugmode' (*note Debug Levels::).
+ * The format of the output from 'dumpdef' and macro tracing can be
+ controlled with 'debugmode' (*note Debug Levels::).
* The destination of trace and debug output can be controlled with
- `debugfile' (*note Debug Output::).
+ 'debugfile' (*note Debug Output::).
- * The `maketemp' (*note Mkstemp::) macro behaves like `mkstemp',
+ * The 'maketemp' (*note Mkstemp::) macro behaves like 'mkstemp',
creating a new file with a unique name on every invocation, rather
- than following the insecure behavior of replacing the trailing `X'
- characters with the `m4' process id.
+ than following the insecure behavior of replacing the trailing 'X'
+ characters with the 'm4' process id.
- * POSIX only requires support for the command line options `-s',
- `-D', and `-U', so all other options accepted by GNU M4 are
+ * POSIX only requires support for the command line options '-s',
+ '-D', and '-U', so all other options accepted by GNU M4 are
extensions. *Note Invoking m4::, for a description of these
options.
- The debugging and tracing facilities in GNU `m4' are much more
- extensive than in most other versions of `m4'.
+ The debugging and tracing facilities in GNU 'm4' are much more
+ extensive than in most other versions of 'm4'.
\1f
File: m4.info, Node: Incompatibilities, Next: Other Incompatibilities, Prev: Extensions, Up: Compatibility
-16.2 Facilities in System V `m4' not in GNU `m4'
+16.2 Facilities in System V 'm4' not in GNU 'm4'
================================================
-The version of `m4' from System V contains a few facilities that have
-not been implemented in GNU `m4' yet. Additionally, POSIX requires
-some behaviors that GNU `m4' has not implemented yet. Relying on these
-behaviors is non-portable, as a future release of GNU `m4' may change.
+The version of 'm4' from System V contains a few facilities that have
+not been implemented in GNU 'm4' yet. Additionally, POSIX requires some
+behaviors that GNU 'm4' has not implemented yet. Relying on these
+behaviors is non-portable, as a future release of GNU 'm4' may change.
- * POSIX requires support for multiple arguments to `defn', without
- any clarification on how `defn' behaves when one of the multiple
- arguments names a builtin. System V `m4' and some other
+ * POSIX requires support for multiple arguments to 'defn', without
+ any clarification on how 'defn' behaves when one of the multiple
+ arguments names a builtin. System V 'm4' and some other
implementations allow mixing builtins and text macros into a single
- macro. GNU `m4' only supports joining multiple text arguments,
+ macro. GNU 'm4' only supports joining multiple text arguments,
although a future implementation may lift this restriction to
behave more like System V. The only portable way to join text
macros with builtins is via helper macros and implicit
* POSIX requires an application to exit with non-zero status if it
wrote an error message to stderr. This has not yet been
- consistently implemented for the various builtins that are
- required to issue an error (such as `eval' (*note Eval::) when an
- argument cannot be parsed).
+ consistently implemented for the various builtins that are required
+ to issue an error (such as 'eval' (*note Eval::) when an argument
+ cannot be parsed).
* Some traditional implementations only allow reading standard input
- once, but GNU `m4' correctly handles multiple instances of `-' on
+ once, but GNU 'm4' correctly handles multiple instances of '-' on
the command line.
- * POSIX requires `m4wrap' (*note M4wrap::) to act in FIFO (first-in,
- first-out) order, but GNU `m4' currently uses LIFO order.
- Furthermore, POSIX states that only the first argument to `m4wrap'
- is saved for later evaluation, but GNU `m4' saves and processes
- all arguments, with output separated by spaces.
+ * POSIX requires 'm4wrap' (*note M4wrap::) to act in FIFO (first-in,
+ first-out) order, but GNU 'm4' currently uses LIFO order.
+ Furthermore, POSIX states that only the first argument to 'm4wrap'
+ is saved for later evaluation, but GNU 'm4' saves and processes all
+ arguments, with output separated by spaces.
* POSIX states that builtins that require arguments, but are called
without arguments, have undefined behavior. Traditional
implementations simply behave as though empty strings had been
- passed. For example, `a`'define`'b' would expand to `ab'. But
- GNU `m4' ignores certain builtins if they have missing arguments,
- giving `adefineb' for the above example.
+ passed. For example, 'a`'define`'b' would expand to 'ab'. But GNU
+ 'm4' ignores certain builtins if they have missing arguments,
+ giving 'adefineb' for the above example.
- * Traditional implementations handle `define(`f',`1')' (*note
+ * Traditional implementations handle 'define(`f',`1')' (*note
Define::) by undefining the entire stack of previous definitions,
- and if doing `undefine(`f')' first. GNU `m4' replaces just the top
- definition on the stack, as if doing `popdef(`f')' followed by
- `pushdef(`f',`1')'. POSIX allows either behavior.
+ and if doing 'undefine(`f')' first. GNU 'm4' replaces just the top
+ definition on the stack, as if doing 'popdef(`f')' followed by
+ 'pushdef(`f',`1')'. POSIX allows either behavior.
- * POSIX 2001 requires `syscmd' (*note Syscmd::) to evaluate command
+ * POSIX 2001 requires 'syscmd' (*note Syscmd::) to evaluate command
output for macro expansion, but this was a mistake that is
- anticipated to be corrected in the next version of POSIX. GNU
- `m4' follows traditional behavior in `syscmd' where output is not
- rescanned, and provides the extension `esyscmd' that does scan the
+ anticipated to be corrected in the next version of POSIX. GNU 'm4'
+ follows traditional behavior in 'syscmd' where output is not
+ rescanned, and provides the extension 'esyscmd' that does scan the
output.
- * At one point, POSIX required `changequote(ARG)' (*note
+ * At one point, POSIX required 'changequote(ARG)' (*note
Changequote::) to use newline as the close quote, but this was a
bug, and the next version of POSIX is anticipated to state that
using empty strings or just one argument is unspecified.
- Meanwhile, the GNU `m4' behavior of treating an empty end-quote
- delimiter as `'' is not portable, as Solaris treats it as
- repeating the start-quote delimiter, and BSD treats it as leaving
- the previous end-quote delimiter unchanged. For predictable
- results, never call changequote with just one argument, or with
- empty strings for arguments.
-
- * At one point, POSIX required `changecom(ARG,)' (*note Changecom::)
+ Meanwhile, the GNU 'm4' behavior of treating an empty end-quote
+ delimiter as ''' is not portable, as Solaris treats it as repeating
+ the start-quote delimiter, and BSD treats it as leaving the
+ previous end-quote delimiter unchanged. For predictable results,
+ never call changequote with just one argument, or with empty
+ strings for arguments.
+
+ * At one point, POSIX required 'changecom(ARG,)' (*note Changecom::)
to make it impossible to end a comment, but this is a bug, and the
next version of POSIX is anticipated to state that using empty
- strings is unspecified. Meanwhile, the GNU `m4' behavior of
- treating an empty end-comment delimiter as newline is not
- portable, as BSD treats it as leaving the previous end-comment
- delimiter unchanged. It is also impossible in BSD implementations
- to disable comments, even though that is required by POSIX. For
- predictable results, never call changecom with empty strings for
- arguments.
-
- * Most implementations of `m4' give macros a higher precedence than
+ strings is unspecified. Meanwhile, the GNU 'm4' behavior of
+ treating an empty end-comment delimiter as newline is not portable,
+ as BSD treats it as leaving the previous end-comment delimiter
+ unchanged. It is also impossible in BSD implementations to disable
+ comments, even though that is required by POSIX. For predictable
+ results, never call changecom with empty strings for arguments.
+
+ * Most implementations of 'm4' give macros a higher precedence than
comments when parsing, meaning that if the start delimiter given to
- `changecom' (*note Changecom::) starts with a macro name, comments
+ 'changecom' (*note Changecom::) starts with a macro name, comments
are effectively disabled. POSIX does not specify what the
- precedence is, so this version of GNU `m4' parser recognizes
+ precedence is, so this version of GNU 'm4' parser recognizes
comments, then macros, then quoted strings.
* Traditional implementations allow argument collection, but not
string and comment processing, to span file boundaries. Thus, if
- `a.m4' contains `len(', and `b.m4' contains `abc)', `m4 a.m4 b.m4'
- outputs `3' with traditional `m4', but gives an error message that
- the end of file was encountered inside a macro with GNU `m4'. On
+ 'a.m4' contains 'len(', and 'b.m4' contains 'abc)', 'm4 a.m4 b.m4'
+ outputs '3' with traditional 'm4', but gives an error message that
+ the end of file was encountered inside a macro with GNU 'm4'. On
the other hand, traditional implementations do end of file
- processing for files included with `include' or `sinclude' (*note
- Include::), while GNU `m4' seamlessly integrates the content of
- those files. Thus `include(`a.m4')include(`b.m4')' will output
- `3' instead of giving an error.
-
- * Traditional `m4' treats `traceon' (*note Trace::) without
- arguments as a global variable, independent of named macro tracing.
- Also, once a macro is undefined, named tracing of that macro is
- lost. On the other hand, when GNU `m4' encounters `traceon'
- without arguments, it turns tracing on for all existing
- definitions at the time, but does not trace future definitions;
- `traceoff' without arguments turns tracing off for all definitions
- regardless of whether they were also traced by name; and tracing
- by name, such as with `-tfoo' at the command line or
- `traceon(`foo')' in the input, is an attribute that is preserved
- even if the macro is currently undefined.
+ processing for files included with 'include' or 'sinclude' (*note
+ Include::), while GNU 'm4' seamlessly integrates the content of
+ those files. Thus 'include(`a.m4')include(`b.m4')' will output '3'
+ instead of giving an error.
+
+ * Traditional 'm4' treats 'traceon' (*note Trace::) without arguments
+ as a global variable, independent of named macro tracing. Also,
+ once a macro is undefined, named tracing of that macro is lost. On
+ the other hand, when GNU 'm4' encounters 'traceon' without
+ arguments, it turns tracing on for all existing definitions at the
+ time, but does not trace future definitions; 'traceoff' without
+ arguments turns tracing off for all definitions regardless of
+ whether they were also traced by name; and tracing by name, such as
+ with '-tfoo' at the command line or 'traceon(`foo')' in the input,
+ is an attribute that is preserved even if the macro is currently
+ undefined.
Additionally, while POSIX requires trace output, it makes no
demands on the formatting of that output. Parsing trace output is
not guaranteed to be reliable, even between different releases of
GNU M4; however, the intent is that any future changes in trace
output will only occur under the direction of additional
- `debugmode' flags (*note Debug Levels::).
+ 'debugmode' flags (*note Debug Levels::).
- * POSIX requires `eval' (*note Eval::) to treat all operators with
- the same precedence as C. However, earlier versions of GNU `m4'
- followed the traditional behavior of other `m4' implementations,
- where bitwise and logical negation (`~' and `!') have lower
+ * POSIX requires 'eval' (*note Eval::) to treat all operators with
+ the same precedence as C. However, earlier versions of GNU 'm4'
+ followed the traditional behavior of other 'm4' implementations,
+ where bitwise and logical negation ('~' and '!') have lower
precedence than equality operators; and where equality operators
- (`==' and `!=') had the same precedence as relational operators
- (such as `<'). Use explicit parentheses to ensure proper
- precedence. As extensions to POSIX, GNU `m4' gives well-defined
+ ('==' and '!=') had the same precedence as relational operators
+ (such as '<'). Use explicit parentheses to ensure proper
+ precedence. As extensions to POSIX, GNU 'm4' gives well-defined
semantics to operations that C leaves undefined, such as when
- overflow occurs, when shifting negative numbers, or when
- performing division by zero. POSIX also requires `=' to cause an
- error, but many traditional implementations allowed it as an alias
- for `=='.
+ overflow occurs, when shifting negative numbers, or when performing
+ division by zero. POSIX also requires '=' to cause an error, but
+ many traditional implementations allowed it as an alias for '=='.
- * POSIX 2001 requires `translit' (*note Translit::) to treat each
- character of the second and third arguments literally. However,
- it is anticipated that the next version of POSIX will allow the
- GNU `m4' behavior of treating `-' as a range operator.
+ * POSIX 2001 requires 'translit' (*note Translit::) to treat each
+ character of the second and third arguments literally. However, it
+ is anticipated that the next version of POSIX will allow the GNU
+ 'm4' behavior of treating '-' as a range operator.
- * POSIX requires `m4' to honor the locale environment variables of
- `LANG', `LC_ALL', `LC_CTYPE', `LC_MESSAGES', and `NLSPATH', but
- this has not yet been implemented in GNU `m4'.
+ * POSIX requires 'm4' to honor the locale environment variables of
+ 'LANG', 'LC_ALL', 'LC_CTYPE', 'LC_MESSAGES', and 'NLSPATH', but
+ this has not yet been implemented in GNU 'm4'.
* POSIX states that only unquoted leading newlines and blanks (that
is, space and tab) are ignored when collecting macro arguments.
However, this appears to be a bug in POSIX, since most traditional
implementations also ignore all whitespace (formfeed, carriage
- return, and vertical tab). GNU `m4' follows tradition and ignores
+ return, and vertical tab). GNU 'm4' follows tradition and ignores
all leading unquoted whitespace.
* A strictly-compliant POSIX client is not allowed to use
- command-line arguments not specified by POSIX. However, since
- this version of M4 ignores `POSIXLY_CORRECT' and enables the option
- `--gnu' by default (*note Invoking m4: Limits control.), a client
+ command-line arguments not specified by POSIX. However, since this
+ version of M4 ignores 'POSIXLY_CORRECT' and enables the option
+ '--gnu' by default (*note Invoking m4: Limits control.), a client
desiring to be strictly compliant has no way to disable GNU
extensions that conflict with POSIX when directly invoking the
- compiled `m4'. A future version of `GNU' M4 will honor the
- environment variable `POSIXLY_CORRECT', implicitly enabling
- `--traditional' if it is set, in order to allow a
+ compiled 'm4'. A future version of 'GNU' M4 will honor the
+ environment variable 'POSIXLY_CORRECT', implicitly enabling
+ '--traditional' if it is set, in order to allow a
strictly-compliant client. In the meantime, a client needing
strict POSIX compliance can use the workaround of invoking a shell
- script wrapper, where the wrapper then adds `--traditional' to the
- arguments passed to the compiled `m4'.
+ script wrapper, where the wrapper then adds '--traditional' to the
+ arguments passed to the compiled 'm4'.
\1f
File: m4.info, Node: Other Incompatibilities, Prev: Incompatibilities, Up: Compatibility
============================
There are a few other incompatibilities between this implementation of
-`m4', and the System V version.
+'m4', and the System V version.
- * GNU `m4' implements sync lines differently from System V `m4',
- when text is being diverted. GNU `m4' outputs the sync lines when
- the text is being diverted, and System V `m4' when the diverted
- text is being brought back.
+ * GNU 'm4' implements sync lines differently from System V 'm4', when
+ text is being diverted. GNU 'm4' outputs the sync lines when the
+ text is being diverted, and System V 'm4' when the diverted text is
+ being brought back.
The problem is which lines and file names should be attached to
- text that is being, or has been, diverted. System V `m4' regards
+ text that is being, or has been, diverted. System V 'm4' regards
all the diverted text as being generated by the source line
- containing the `undivert' call, whereas GNU `m4' regards the
+ containing the 'undivert' call, whereas GNU 'm4' regards the
diverted text as being generated at the time it is diverted.
- The sync line option is used mostly when using `m4' as a front end
+ The sync line option is used mostly when using 'm4' as a front end
to a compiler. If a diverted line causes a compiler error, the
error messages should most probably refer to the place where the
diversion was made, and not where it was inserted again.
=>#line 1 "stdin"
=>2
- The current `m4' implementation has a limitation that the syncline
+ The current 'm4' implementation has a limitation that the syncline
output at the start of each diversion occurs no matter what, even
if the previous diversion did not end with a newline. This goes
contrary to the claim that synclines appear on a line by
- themselves, so this limitation may be corrected in a future
- version of `m4'. In the meantime, when using `-s', it is wisest
- to make sure all diversions end with newline.
+ themselves, so this limitation may be corrected in a future version
+ of 'm4'. In the meantime, when using '-s', it is wisest to make
+ sure all diversions end with newline.
- * GNU `m4' makes no attempt at prohibiting self-referential
+ * GNU 'm4' makes no attempt at prohibiting self-referential
definitions like:
define(`x', `x')
define(`x', `x ')
=>
- There is nothing inherently wrong with defining `x' to return `x'.
- The wrong thing is to expand `x' unquoted, because that would
- cause an infinite rescan loop. In `m4', one might use macros to
- hold strings, as we do for variables in other programming
- languages, further checking them with:
+ There is nothing inherently wrong with defining 'x' to return 'x'.
+ The wrong thing is to expand 'x' unquoted, because that would cause
+ an infinite rescan loop. In 'm4', one might use macros to hold
+ strings, as we do for variables in other programming languages,
+ further checking them with:
ifelse(defn(`HOLDER'), `VALUE', ...)
- In cases like this one, an interdiction for a macro to hold its
- own name would be a useless limitation. Of course, this leaves
- more rope for the GNU `m4' user to hang himself! Rescanning hangs
- may be avoided through careful programming, a little like for
- endless loops in traditional programming languages.
+ In cases like this one, an interdiction for a macro to hold its own
+ name would be a useless limitation. Of course, this leaves more
+ rope for the GNU 'm4' user to hang himself! Rescanning hangs may
+ be avoided through careful programming, a little like for endless
+ loops in traditional programming languages.
\1f
File: m4.info, Node: Answers, Next: Copying This Package, Prev: Compatibility, Up: Top
* Menu:
-* Improved exch:: Solution for `exch'
-* Improved forloop:: Solution for `forloop'
-* Improved foreach:: Solution for `foreach'
-* Improved copy:: Solution for `copy'
-* Improved m4wrap:: Solution for `m4wrap'
-* Improved cleardivert:: Solution for `cleardivert'
-* Improved capitalize:: Solution for `capitalize'
-* Improved fatal_error:: Solution for `fatal_error'
+* Improved exch:: Solution for 'exch'
+* Improved forloop:: Solution for 'forloop'
+* Improved foreach:: Solution for 'foreach'
+* Improved copy:: Solution for 'copy'
+* Improved m4wrap:: Solution for 'm4wrap'
+* Improved cleardivert:: Solution for 'cleardivert'
+* Improved capitalize:: Solution for 'capitalize'
+* Improved fatal_error:: Solution for 'fatal_error'
\1f
File: m4.info, Node: Improved exch, Next: Improved forloop, Up: Answers
-17.1 Solution for `exch'
+17.1 Solution for 'exch'
========================
-The `exch' macro (*note Arguments::) as presented requires clients to
+The 'exch' macro (*note Arguments::) as presented requires clients to
double quote their arguments. A nicer definition, which lets clients
follow the rule of thumb of one level of quoting per level of
-parentheses, involves adding quotes in the definition of `exch', as
+parentheses, involves adding quotes in the definition of 'exch', as
follows:
define(`exch', ``$2', `$1'')
\1f
File: m4.info, Node: Improved forloop, Next: Improved foreach, Prev: Improved exch, Up: Answers
-17.2 Solution for `forloop'
+17.2 Solution for 'forloop'
===========================
-The `forloop' macro (*note Forloop::) as presented earlier can go into
+The 'forloop' macro (*note Forloop::) as presented earlier can go into
an infinite loop if given an iterator that is not parsed as a macro
name. It does not do any sanity checking on its numeric bounds, and
only permits decimal numbers for bounds. Here is an improved version,
-shipped as `m4-1.4.16/examples/forloop2.m4'; this version also
-optimizes overhead by calling four macros instead of six per iteration
-(excluding those in TEXT), by not dereferencing the ITERATOR in the
-helper `_forloop'.
+shipped as 'm4-1.4.17/examples/forloop2.m4'; this version also optimizes
+overhead by calling four macros instead of six per iteration (excluding
+those in TEXT), by not dereferencing the ITERATOR in the helper
+'_forloop'.
$ m4 -d -I examples
undivert(`forloop2.m4')dnl
forloop(`i', `5 + 5', `0xc', ` 0x`'eval(i, `16')')
=> 0xa 0xb 0xc
forloop(`i', `a', `b', `non-numeric bounds')
- error-->m4:stdin:6: bad expression in eval (bad input): (a) <= (b)
+ error->m4:stdin:6: bad expression in eval (bad input): (a) <= (b)
=>
- One other change to notice is that the improved version used `_$0'
-rather than `_foreach' to invoke the helper routine. In general, this
+ One other change to notice is that the improved version used '_$0'
+rather than '_foreach' to invoke the helper routine. In general, this
is a good practice to follow, because then the set of macros can be
uniformly transformed. The following example shows a transformation
-that doubles the current quoting and appends a suffix `2' to each
-transformed macro. If `foreach' refers to the literal `_foreach', then
-`foreach2' invokes `_foreach' instead of the intended `_foreach2', and
+that doubles the current quoting and appends a suffix '2' to each
+transformed macro. If 'foreach' refers to the literal '_foreach', then
+'foreach2' invokes '_foreach' instead of the intended '_foreach2', and
the mixing of quoting paradigms leads to an infinite recursion loop in
this example.
changequote(`[', `]')changequote([``], [''])
=>
forloop2(i, 1, 5, ``ifelse('')forloop2(i, 1, 5, ``)'')
- error-->m4:stdin:12: recursion limit of 9 exceeded, use -L<N> to change it
+ error->m4:stdin:12: recursion limit of 9 exceeded, use -L<N> to change it
One more optimization is still possible. Instead of repeatedly
assigning a variable then invoking or dereferencing it, it is possible
to pass the current iterator value as a single argument. Coupled with
-`curry' if other arguments are needed (*note Composition::), or with
+'curry' if other arguments are needed (*note Composition::), or with
helper macros if the argument is needed in more than one place in the
expansion, the output can be generated with three, rather than four,
macros of overhead per iteration. Notice how the file
-`m4-1.4.16/examples/forloop3.m4' rearranges the arguments of the helper
-`_forloop' to take two arguments that are placed around the current
+'m4-1.4.17/examples/forloop3.m4' rearranges the arguments of the helper
+'_forloop' to take two arguments that are placed around the current
value. By splitting a balanced set of parantheses across multiple
-arguments, the helper macro can now be shared by `forloop' and the new
-`forloop_arg'.
+arguments, the helper macro can now be shared by 'forloop' and the new
+'forloop_arg'.
$ m4 -I examples
include(`forloop3.m4')
Of course, it is possible to make even more improvements, such as
adding an optional step argument, or allowing iteration through
descending sequences. GNU Autoconf provides some of these additional
-bells and whistles in its `m4_for' macro.
+bells and whistles in its 'm4_for' macro.
\1f
File: m4.info, Node: Improved foreach, Next: Improved copy, Prev: Improved forloop, Up: Answers
-17.3 Solution for `foreach'
+17.3 Solution for 'foreach'
===========================
-The `foreach' and `foreachq' macros (*note Foreach::) as presented
+The 'foreach' and 'foreachq' macros (*note Foreach::) as presented
earlier each have flaws. First, we will examine and fix the quadratic
-behavior of `foreachq':
+behavior of 'foreachq':
$ m4 -I examples
include(`foreachq.m4')
foreachq(`x', ``1', `2', `3', `4'', `x
')dnl
=>1
- error-->m4trace: -3- shift(`1', `2', `3', `4')
- error-->m4trace: -2- shift(`1', `2', `3', `4')
+ error->m4trace: -3- shift(`1', `2', `3', `4')
+ error->m4trace: -2- shift(`1', `2', `3', `4')
=>2
- error-->m4trace: -4- shift(`1', `2', `3', `4')
- error-->m4trace: -3- shift(`2', `3', `4')
- error-->m4trace: -3- shift(`1', `2', `3', `4')
- error-->m4trace: -2- shift(`2', `3', `4')
+ error->m4trace: -4- shift(`1', `2', `3', `4')
+ error->m4trace: -3- shift(`2', `3', `4')
+ error->m4trace: -3- shift(`1', `2', `3', `4')
+ error->m4trace: -2- shift(`2', `3', `4')
=>3
- error-->m4trace: -5- shift(`1', `2', `3', `4')
- error-->m4trace: -4- shift(`2', `3', `4')
- error-->m4trace: -3- shift(`3', `4')
- error-->m4trace: -4- shift(`1', `2', `3', `4')
- error-->m4trace: -3- shift(`2', `3', `4')
- error-->m4trace: -2- shift(`3', `4')
+ error->m4trace: -5- shift(`1', `2', `3', `4')
+ error->m4trace: -4- shift(`2', `3', `4')
+ error->m4trace: -3- shift(`3', `4')
+ error->m4trace: -4- shift(`1', `2', `3', `4')
+ error->m4trace: -3- shift(`2', `3', `4')
+ error->m4trace: -2- shift(`3', `4')
=>4
- error-->m4trace: -6- shift(`1', `2', `3', `4')
- error-->m4trace: -5- shift(`2', `3', `4')
- error-->m4trace: -4- shift(`3', `4')
- error-->m4trace: -3- shift(`4')
-
- Each successive iteration was adding more quoted `shift'
-invocations, and the entire list contents were passing through every
-iteration. In general, when recursing, it is a good idea to make the
-recursion use fewer arguments, rather than adding additional quoted
-uses of `shift'. By doing so, `m4' uses less memory, invokes fewer
-macros, is less likely to run into machine limits, and most
-importantly, performs faster. The fixed version of `foreachq' can be
-found in `m4-1.4.16/examples/foreachq2.m4':
+ error->m4trace: -6- shift(`1', `2', `3', `4')
+ error->m4trace: -5- shift(`2', `3', `4')
+ error->m4trace: -4- shift(`3', `4')
+ error->m4trace: -3- shift(`4')
+
+ Each successive iteration was adding more quoted 'shift' invocations,
+and the entire list contents were passing through every iteration. In
+general, when recursing, it is a good idea to make the recursion use
+fewer arguments, rather than adding additional quoted uses of 'shift'.
+By doing so, 'm4' uses less memory, invokes fewer macros, is less likely
+to run into machine limits, and most importantly, performs faster. The
+fixed version of 'foreachq' can be found in
+'m4-1.4.17/examples/foreachq2.m4':
$ m4 -I examples
include(`foreachq2.m4')
foreachq(`x', ``1', `2', `3', `4'', `x
')dnl
=>1
- error-->m4trace: -3- shift(`1', `2', `3', `4')
+ error->m4trace: -3- shift(`1', `2', `3', `4')
=>2
- error-->m4trace: -3- shift(`2', `3', `4')
+ error->m4trace: -3- shift(`2', `3', `4')
=>3
- error-->m4trace: -3- shift(`3', `4')
+ error->m4trace: -3- shift(`3', `4')
=>4
Note that the fixed version calls unquoted helper macros in
-`_foreachq' to trim elements immediately; those helper macros in turn
+'_foreachq' to trim elements immediately; those helper macros in turn
must re-supply the layer of quotes lost in the macro invocation.
-Contrast the use of `_arg1q', which quotes the first list element, with
-`_arg1' of the earlier implementation that returned the first list
+Contrast the use of '_arg1q', which quotes the first list element, with
+'_arg1' of the earlier implementation that returned the first list
element directly. Additionally, by calling the helper method
-immediately, the `defn(`ITERATOR')' no longer contains unexpanded
+immediately, the 'defn(`ITERATOR')' no longer contains unexpanded
macros.
The astute m4 programmer might notice that the solution above still
uses more memory and macro invocations, and thus more time, than
-strictly necessary. Note that `$2', which contains an arbitrarily long
+strictly necessary. Note that '$2', which contains an arbitrarily long
quoted list, is expanded and rescanned three times per iteration of
-`_foreachq'. Furthermore, every iteration of the algorithm effectively
+'_foreachq'. Furthermore, every iteration of the algorithm effectively
unboxes then reboxes the list, which costs a couple of macro
invocations. It is possible to rewrite the algorithm for a bit more
-speed by swapping the order of the arguments to `_foreachq' in order to
+speed by swapping the order of the arguments to '_foreachq' in order to
operate on an unboxed list in the first place, and by using the
-fixed-length `$#' instead of an arbitrary length list as the key to end
+fixed-length '$#' instead of an arbitrary length list as the key to end
recursion. The result is an overhead of six macro invocations per loop
(excluding any macros in TEXT), instead of eight. This alternative
-approach is available as `m4-1.4.16/examples/foreach3.m4':
+approach is available as 'm4-1.4.17/examples/foreach3.m4':
$ m4 -I examples
include(`foreachq3.m4')
foreachq(`x', ``1', `2', `3', `4'', `x
')dnl
=>1
- error-->m4trace: -4- shift(`x', `x
- error-->', `', `1', `2', `3', `4')
- error-->m4trace: -3- shift(`x
- error-->', `', `1', `2', `3', `4')
- error-->m4trace: -2- shift(`', `1', `2', `3', `4')
+ error->m4trace: -4- shift(`x', `x
+ error->', `', `1', `2', `3', `4')
+ error->m4trace: -3- shift(`x
+ error->', `', `1', `2', `3', `4')
+ error->m4trace: -2- shift(`', `1', `2', `3', `4')
=>2
- error-->m4trace: -4- shift(`x', `x
- error-->', `1', `2', `3', `4')
- error-->m4trace: -3- shift(`x
- error-->', `1', `2', `3', `4')
- error-->m4trace: -2- shift(`1', `2', `3', `4')
+ error->m4trace: -4- shift(`x', `x
+ error->', `1', `2', `3', `4')
+ error->m4trace: -3- shift(`x
+ error->', `1', `2', `3', `4')
+ error->m4trace: -2- shift(`1', `2', `3', `4')
=>3
- error-->m4trace: -4- shift(`x', `x
- error-->', `2', `3', `4')
- error-->m4trace: -3- shift(`x
- error-->', `2', `3', `4')
- error-->m4trace: -2- shift(`2', `3', `4')
+ error->m4trace: -4- shift(`x', `x
+ error->', `2', `3', `4')
+ error->m4trace: -3- shift(`x
+ error->', `2', `3', `4')
+ error->m4trace: -2- shift(`2', `3', `4')
=>4
- error-->m4trace: -4- shift(`x', `x
- error-->', `3', `4')
- error-->m4trace: -3- shift(`x
- error-->', `3', `4')
- error-->m4trace: -2- shift(`3', `4')
-
- In the current version of M4, every instance of `$@' is rescanned as
-it is encountered. Thus, the `foreachq3.m4' alternative uses much less
-memory than `foreachq2.m4', and executes as much as 10% faster, since
-each iteration encounters fewer `$@'. However, the implementation of
-rescanning every byte in `$@' is quadratic in the number of bytes
-scanned (for example, making the broken version in `foreachq.m4' cubic,
+ error->m4trace: -4- shift(`x', `x
+ error->', `3', `4')
+ error->m4trace: -3- shift(`x
+ error->', `3', `4')
+ error->m4trace: -2- shift(`3', `4')
+
+ In the current version of M4, every instance of '$@' is rescanned as
+it is encountered. Thus, the 'foreachq3.m4' alternative uses much less
+memory than 'foreachq2.m4', and executes as much as 10% faster, since
+each iteration encounters fewer '$@'. However, the implementation of
+rescanning every byte in '$@' is quadratic in the number of bytes
+scanned (for example, making the broken version in 'foreachq.m4' cubic,
rather than quadratic, in behavior). A future release of M4 will
improve the underlying implementation by reusing results of previous
-scans, so that both styles of `foreachq' can become linear in the
-number of bytes scanned. Notice how the implementation injects an
-empty argument prior to expanding `$2' within `foreachq'; the helper
-macro `_foreachq' then ignores the third argument altogether, and ends
+scans, so that both styles of 'foreachq' can become linear in the number
+of bytes scanned. Notice how the implementation injects an empty
+argument prior to expanding '$2' within 'foreachq'; the helper macro
+'_foreachq' then ignores the third argument altogether, and ends
recursion when there are three arguments left because there was nothing
-left to pass through `shift'. Thus, each iteration only needs one
-`ifelse', rather than the two conditionals used in the version from
-`foreachq2.m4'.
+left to pass through 'shift'. Thus, each iteration only needs one
+'ifelse', rather than the two conditionals used in the version from
+'foreachq2.m4'.
- So far, all of the implementations of `foreachq' presented have been
-quadratic with M4 1.4.x. But `forloop' is linear, because each
+ So far, all of the implementations of 'foreachq' presented have been
+quadratic with M4 1.4.x. But 'forloop' is linear, because each
iteration parses a constant amount of arguments. So, it is possible to
-design a variant that uses `forloop' to do the iteration, then uses
-`$@' only once at the end, giving a linear result even with older M4
+design a variant that uses 'forloop' to do the iteration, then uses '$@'
+only once at the end, giving a linear result even with older M4
implementations. This implementation relies on the GNU extension that
-`$10' expands to the tenth argument rather than the first argument
-concatenated with `0'. The trick is to define an intermediate macro
-that repeats the text `m4_define(`$1', `$N')$2`'', with `n' set to
+'$10' expands to the tenth argument rather than the first argument
+concatenated with '0'. The trick is to define an intermediate macro
+that repeats the text 'm4_define(`$1', `$N')$2`'', with 'n' set to
successive integers corresponding to each argument. The helper macro
-`_foreachq_' is needed in order to generate the literal sequences such
-as `$1' into the intermediate macro, rather than expanding them as the
-arguments of `_foreachq'. With this approach, no `shift' calls are
-even needed! Even though there are seven macros of overhead per
-iteration instead of six in `foreachq3.m4', the linear scaling is
-apparent at relatively small list sizes. However, this approach will
-need adjustment when a future version of M4 follows POSIX by no longer
-treating `$10' as the tenth argument; the anticipation is that `${10}'
+'_foreachq_' is needed in order to generate the literal sequences such
+as '$1' into the intermediate macro, rather than expanding them as the
+arguments of '_foreachq'. With this approach, no 'shift' calls are even
+needed! Even though there are seven macros of overhead per iteration
+instead of six in 'foreachq3.m4', the linear scaling is apparent at
+relatively small list sizes. However, this approach will need
+adjustment when a future version of M4 follows POSIX by no longer
+treating '$10' as the tenth argument; the anticipation is that '${10}'
can be used instead, although that alternative syntax is not yet
supported.
=>3
=>4
- For yet another approach, the improved version of `foreach',
-available in `m4-1.4.16/examples/foreach2.m4', simply overquotes the
-arguments to `_foreach' to begin with, using `dquote_elt'. Then
-`_foreach' can just use `_arg1' to remove the extra layer of quoting
+ For yet another approach, the improved version of 'foreach',
+available in 'm4-1.4.17/examples/foreach2.m4', simply overquotes the
+arguments to '_foreach' to begin with, using 'dquote_elt'. Then
+'_foreach' can just use '_arg1' to remove the extra layer of quoting
that was added up front:
$ m4 -I examples
=>
foreach(`x', `(`1', `2', `3', `4')', `x
')dnl
- error-->m4trace: -4- shift(`1', `2', `3', `4')
- error-->m4trace: -4- shift(`2', `3', `4')
- error-->m4trace: -4- shift(`3', `4')
+ error->m4trace: -4- shift(`1', `2', `3', `4')
+ error->m4trace: -4- shift(`2', `3', `4')
+ error->m4trace: -4- shift(`3', `4')
=>1
- error-->m4trace: -3- shift(``1'', ``2'', ``3'', ``4'')
+ error->m4trace: -3- shift(``1'', ``2'', ``3'', ``4'')
=>2
- error-->m4trace: -3- shift(``2'', ``3'', ``4'')
+ error->m4trace: -3- shift(``2'', ``3'', ``4'')
=>3
- error-->m4trace: -3- shift(``3'', ``4'')
+ error->m4trace: -3- shift(``3'', ``4'')
=>4
- error-->m4trace: -3- shift(``4'')
-
- It is likewise possible to write a variant of `foreach' that
-performs in linear time on M4 1.4.x; the easiest method is probably
-writing a version of `foreach' that unboxes its list, then invokes
-`_foreachq' as previously defined in `foreachq4.m4'.
-
- In summary, recursion over list elements is trickier than it
-appeared at first glance, but provides a powerful idiom within `m4'
-processing. As a final demonstration, both list styles are now able to
-handle several scenarios that would wreak havoc on one or both of the
-original implementations. This points out one other difference between
-the list styles. `foreach' evaluates unquoted list elements only once,
-in preparation for calling `_foreach', similary for `foreachq' as
-provided by `foreachq3.m4' or `foreachq4.m4'. But `foreachq', as
-provided by `foreachq2.m4', evaluates unquoted list elements twice
-while visiting the first list element, once in `_arg1q' and once in
-`_rest'. When deciding which list style to use, one must take into
-account whether repeating the side effects of unquoted list elements
-will have any detrimental effects.
+ error->m4trace: -3- shift(``4'')
+
+ It is likewise possible to write a variant of 'foreach' that performs
+in linear time on M4 1.4.x; the easiest method is probably writing a
+version of 'foreach' that unboxes its list, then invokes '_foreachq' as
+previously defined in 'foreachq4.m4'.
+
+ In summary, recursion over list elements is trickier than it appeared
+at first glance, but provides a powerful idiom within 'm4' processing.
+As a final demonstration, both list styles are now able to handle
+several scenarios that would wreak havoc on one or both of the original
+implementations. This points out one other difference between the list
+styles. 'foreach' evaluates unquoted list elements only once, in
+preparation for calling '_foreach', similary for 'foreachq' as provided
+by 'foreachq3.m4' or 'foreachq4.m4'. But 'foreachq', as provided by
+'foreachq2.m4', evaluates unquoted list elements twice while visiting
+the first list element, once in '_arg1q' and once in '_rest'. When
+deciding which list style to use, one must take into account whether
+repeating the side effects of unquoted list elements will have any
+detrimental effects.
$ m4 -I examples
include(`foreach2.m4')
dnl list of unquoted macros; expansion occurs before recursion
foreach(`x', `(active, active)', `<x>
')dnl
- error-->m4trace: -4- active -> `ACT, IVE'
- error-->m4trace: -4- active -> `ACT, IVE'
+ error->m4trace: -4- active -> `ACT, IVE'
+ error->m4trace: -4- active -> `ACT, IVE'
=><ACT>
=><IVE>
=><ACT>
=><IVE>
foreachq(`x', `active, active', `<x>
')dnl
- error-->m4trace: -3- active -> `ACT, IVE'
- error-->m4trace: -3- active -> `ACT, IVE'
+ error->m4trace: -3- active -> `ACT, IVE'
+ error->m4trace: -3- active -> `ACT, IVE'
=><ACT>
- error-->m4trace: -3- active -> `ACT, IVE'
- error-->m4trace: -3- active -> `ACT, IVE'
+ error->m4trace: -3- active -> `ACT, IVE'
+ error->m4trace: -3- active -> `ACT, IVE'
=><IVE>
=><ACT>
=><IVE>
dnl list of quoted macros; expansion occurs during recursion
foreach(`x', `(`active', `active')', `<x>
')dnl
- error-->m4trace: -1- active -> `ACT, IVE'
+ error->m4trace: -1- active -> `ACT, IVE'
=><ACT, IVE>
- error-->m4trace: -1- active -> `ACT, IVE'
+ error->m4trace: -1- active -> `ACT, IVE'
=><ACT, IVE>
foreachq(`x', ``active', `active'', `<x>
')dnl
- error-->m4trace: -1- active -> `ACT, IVE'
+ error->m4trace: -1- active -> `ACT, IVE'
=><ACT, IVE>
- error-->m4trace: -1- active -> `ACT, IVE'
+ error->m4trace: -1- active -> `ACT, IVE'
=><ACT, IVE>
dnl list of double-quoted macro names; no expansion
foreach(`x', `(``active'', ``active'')', `<x>
\1f
File: m4.info, Node: Improved copy, Next: Improved m4wrap, Prev: Improved foreach, Up: Answers
-17.4 Solution for `copy'
+17.4 Solution for 'copy'
========================
-The macro `copy' presented above is unable to handle builtin tokens
-with M4 1.4.x, because it tries to pass the builtin token through the
-macro `curry', where it is silently flattened to an empty string (*note
-Composition::). Rather than using the problematic `curry' to work
-around the limitation that `stack_foreach' expects to invoke a macro
+The macro 'copy' presented above is unable to handle builtin tokens with
+M4 1.4.x, because it tries to pass the builtin token through the macro
+'curry', where it is silently flattened to an empty string (*note
+Composition::). Rather than using the problematic 'curry' to work
+around the limitation that 'stack_foreach' expects to invoke a macro
that takes exactly one argument, we can write a new macro that lets us
-form the exact two-argument `pushdef' call sequence needed, so that we
+form the exact two-argument 'pushdef' call sequence needed, so that we
are no longer passing a builtin token through a text macro.
-- Composite: stack_foreach_sep (MACRO, PRE, POST, SEP)
-- Composite: stack_foreach_sep_lifo (MACRO, PRE, POST, SEP)
- For each of the `pushdef' definitions associated with MACRO,
- expand the sequence `PRE`'definition`'POST'. Additionally, expand
- SEP between definitions. `stack_foreach_sep' visits the oldest
- definition first, while `stack_foreach_sep_lifo' visits the
- current definition first. The expansion may dereference MACRO,
- but should not modify it. There are a few special macros, such as
- `defn', which cannot be used as the MACRO parameter.
-
- Note that `stack_foreach(`MACRO', `ACTION')' is equivalent to
-`stack_foreach_sep(`MACRO', `ACTION(', `)')'. By supplying explicit
+ For each of the 'pushdef' definitions associated with MACRO, expand
+ the sequence 'PRE`'definition`'POST'. Additionally, expand SEP
+ between definitions. 'stack_foreach_sep' visits the oldest
+ definition first, while 'stack_foreach_sep_lifo' visits the current
+ definition first. The expansion may dereference MACRO, but should
+ not modify it. There are a few special macros, such as 'defn',
+ which cannot be used as the MACRO parameter.
+
+ Note that 'stack_foreach(`MACRO', `ACTION')' is equivalent to
+'stack_foreach_sep(`MACRO', `ACTION(', `)')'. By supplying explicit
parentheses, split among the PRE and POST arguments to
-`stack_foreach_sep', it is now possible to construct macro calls with
+'stack_foreach_sep', it is now possible to construct macro calls with
more than one argument, without passing builtin tokens through a macro
call. It is likewise possible to directly reference the stack
definitions without a macro call, by leaving PRE and POST empty. Thus,
-in addition to fixing `copy' on builtin tokens, it also executes with
+in addition to fixing 'copy' on builtin tokens, it also executes with
fewer macro invocations.
The new macro also adds a separator that is only output after the
-first iteration of the helper `_stack_reverse_sep', implemented by
+first iteration of the helper '_stack_reverse_sep', implemented by
prepending the original SEP to PRE and omitting a SEP argument in
subsequent iterations. Note that the empty string that separates SEP
from PRE is provided as part of the fourth argument when originally
-calling `_stack_reverse_sep', and not by writing `$4`'$3' as the third
+calling '_stack_reverse_sep', and not by writing '$4`'$3' as the third
argument in the recursive call; while the other approach would give the
same output, it does so at the expense of increasing the argument size
-on each iteration of `_stack_reverse_sep', which results in quadratic
-instead of linear execution time. The improved stack walking macros
-are available in `m4-1.4.16/examples/stack_sep.m4':
+on each iteration of '_stack_reverse_sep', which results in quadratic
+instead of linear execution time. The improved stack walking macros are
+available in 'm4-1.4.17/examples/stack_sep.m4':
$ m4 -I examples
include(`stack_sep.m4')
\1f
File: m4.info, Node: Improved m4wrap, Next: Improved cleardivert, Prev: Improved copy, Up: Answers
-17.5 Solution for `m4wrap'
+17.5 Solution for 'm4wrap'
==========================
-The replacement `m4wrap' versions presented above, designed to
-guarantee FIFO or LIFO order regardless of the underlying M4
-implementation, share a bug when dealing with wrapped text that looks
-like parameter expansion. Note how the invocation of `m4wrapN'
-interprets these parameters, while using the builtin preserves them for
-their intended use.
+The replacement 'm4wrap' versions presented above, designed to guarantee
+FIFO or LIFO order regardless of the underlying M4 implementation, share
+a bug when dealing with wrapped text that looks like parameter
+expansion. Note how the invocation of 'm4wrapN' interprets these
+parameters, while using the builtin preserves them for their intended
+use.
$ m4 -I examples
include(`wraplifo.m4')
=>bar:-a-a,b-2-
=>m4wrap0:---0-
- Additionally, the computation of `_m4wrap_level' and creation of
-multiple `m4wrapN' placeholders in the original examples is more
+ Additionally, the computation of '_m4wrap_level' and creation of
+multiple 'm4wrapN' placeholders in the original examples is more
expensive in time and memory than strictly necessary. Notice how the
-improved version grabs the wrapped text via `defn' to avoid parameter
-expansion, then undefines `_m4wrap_text', before stripping a level of
-quotes with `_arg1' to expand the text. That way, each level of
+improved version grabs the wrapped text via 'defn' to avoid parameter
+expansion, then undefines '_m4wrap_text', before stripping a level of
+quotes with '_arg1' to expand the text. That way, each level of
wrapping reuses the single placeholder, which starts each nesting level
in an undefined state.
Finally, it is worth emulating the GNU M4 extension of saving all
-arguments to `m4wrap', separated by a space, rather than saving just
-the first argument. This is done with the `join' macro documented
+arguments to 'm4wrap', separated by a space, rather than saving just the
+first argument. This is done with the 'join' macro documented
previously (*note Shift::). The improved LIFO example is shipped as
-`m4-1.4.16/examples/wraplifo2.m4', and can easily be converted to a
-FIFO solution by swapping the adjacent invocations of `joinall' and
-`defn'.
+'m4-1.4.17/examples/wraplifo2.m4', and can easily be converted to a FIFO
+solution by swapping the adjacent invocations of 'joinall' and 'defn'.
$ m4 -I examples
include(`wraplifo2.m4')
\1f
File: m4.info, Node: Improved cleardivert, Next: Improved capitalize, Prev: Improved m4wrap, Up: Answers
-17.6 Solution for `cleardivert'
+17.6 Solution for 'cleardivert'
===============================
-The `cleardivert' macro (*note Cleardivert::) cannot, as it stands, be
+The 'cleardivert' macro (*note Cleardivert::) cannot, as it stands, be
called without arguments to clear all pending diversions. That is
because using undivert with an empty string for an argument is different
than using it with no arguments at all. Compare the earlier definition
\1f
File: m4.info, Node: Improved capitalize, Next: Improved fatal_error, Prev: Improved cleardivert, Up: Answers
-17.7 Solution for `capitalize'
+17.7 Solution for 'capitalize'
==============================
-The `capitalize' macro (*note Patsubst::) as presented earlier does not
+The 'capitalize' macro (*note Patsubst::) as presented earlier does not
allow clients to follow the quoting rule of thumb. Consider the three
-macros `active', `Active', and `ACTIVE', and the difference between
-calling `capitalize' with the expansion of a macro, expanding the
-result of a case change, and changing the case of a double-quoted
-string:
+macros 'active', 'Active', and 'ACTIVE', and the difference between
+calling 'capitalize' with the expansion of a macro, expanding the result
+of a case change, and changing the case of a double-quoted string:
$ m4 -I examples
include(`capitalize.m4')dnl
capitalize(`active')
=>OOPSctive
- First, when `capitalize' is called with more than one argument, it
-was throwing away later arguments, whereas `upcase' and `downcase' used
-`$*' to collect them all. The fix is simple: use `$*' consistently.
+ First, when 'capitalize' is called with more than one argument, it
+was throwing away later arguments, whereas 'upcase' and 'downcase' used
+'$*' to collect them all. The fix is simple: use '$*' consistently.
- Next, with single-quoting, `capitalize' outputs a single character,
-a set of quotes, then the rest of the characters, making it impossible
-to invoke `Active' after the fact, and allowing the alternate macro `A'
-to interfere. Here, the solution is to use additional quoting in the
+ Next, with single-quoting, 'capitalize' outputs a single character, a
+set of quotes, then the rest of the characters, making it impossible to
+invoke 'Active' after the fact, and allowing the alternate macro 'A' to
+interfere. Here, the solution is to use additional quoting in the
helper macros, then pass the final over-quoted output string through
-`_arg1' to remove the extra quoting and finally invoke the concatenated
+'_arg1' to remove the extra quoting and finally invoke the concatenated
portions as a single string.
Finally, when passed a double-quoted string, the nested macro
-`_capitalize' is never invoked because it ended up nested inside
-quotes. This one is the toughest to fix. In short, we have no idea how
-many levels of quotes are in effect on the substring being altered by
-`patsubst'. If the replacement string cannot be expressed entirely in
+'_capitalize' is never invoked because it ended up nested inside quotes.
+This one is the toughest to fix. In short, we have no idea how many
+levels of quotes are in effect on the substring being altered by
+'patsubst'. If the replacement string cannot be expressed entirely in
terms of literal text and backslash substitutions, then we need a
mechanism to guarantee that the helper macros are invoked outside of
-quotes. In other words, this sounds like a job for `changequote'
-(*note Changequote::). By changing the active quoting characters, we
-can guarantee that replacement text injected by `patsubst' always
-occurs in the middle of a string that has exactly one level of
-over-quoting using alternate quotes; so the replacement text closes the
-quoted string, invokes the helper macros, then reopens the quoted
-string. In turn, that means the replacement text has unbalanced quotes,
-necessitating another round of `changequote'.
+quotes. In other words, this sounds like a job for 'changequote' (*note
+Changequote::). By changing the active quoting characters, we can
+guarantee that replacement text injected by 'patsubst' always occurs in
+the middle of a string that has exactly one level of over-quoting using
+alternate quotes; so the replacement text closes the quoted string,
+invokes the helper macros, then reopens the quoted string. In turn,
+that means the replacement text has unbalanced quotes, necessitating
+another round of 'changequote'.
In the fixed version below, (also shipped as
-`m4-1.4.16/examples/capitalize2.m4'), `capitalize' uses the alternate
-quotes of `<<[' and `]>>' (the longer strings are chosen so as to be
+'m4-1.4.17/examples/capitalize2.m4'), 'capitalize' uses the alternate
+quotes of '<<[' and ']>>' (the longer strings are chosen so as to be
less likely to appear in the text being converted). The helpers
-`_to_alt' and `_from_alt' merely reduce the number of characters
-required to perform a `changequote', since the definition changes
-twice. The outermost pair means that `patsubst' and `_capitalize_alt'
-are invoked with alternate quoting; the innermost pair is used so that
-the third argument to `patsubst' can contain an unbalanced `]>>'/`<<['
-pair. Note that `upcase' and `downcase' must be redefined as
-`_upcase_alt' and `_downcase_alt', since they contain nested quotes but
-are invoked with the alternate quoting scheme in effect.
+'_to_alt' and '_from_alt' merely reduce the number of characters
+required to perform a 'changequote', since the definition changes twice.
+The outermost pair means that 'patsubst' and '_capitalize_alt' are
+invoked with alternate quoting; the innermost pair is used so that the
+third argument to 'patsubst' can contain an unbalanced ']>>'/'<<[' pair.
+Note that 'upcase' and 'downcase' must be redefined as '_upcase_alt' and
+'_downcase_alt', since they contain nested quotes but are invoked with
+the alternate quoting scheme in effect.
$ m4 -I examples
include(`capitalize2.m4')dnl
\1f
File: m4.info, Node: Improved fatal_error, Prev: Improved capitalize, Up: Answers
-17.8 Solution for `fatal_error'
+17.8 Solution for 'fatal_error'
===============================
-The `fatal_error' macro (*note M4exit::) is not robust to versions of
-GNU M4 earlier than 1.4.8, where invoking `__file__' (*note Location::)
-inside `m4wrap' would result in an empty string, and `__line__'
-resulted in `0' even though all files start at line 1. Furthermore,
-versions earlier than 1.4.6 did not support the `__program__' macro.
-If you want `fatal_error' to work across the entire 1.4.x release
-series, a better implementation would be:
+The 'fatal_error' macro (*note M4exit::) is not robust to versions of
+GNU M4 earlier than 1.4.8, where invoking '__file__' (*note Location::)
+inside 'm4wrap' would result in an empty string, and '__line__' resulted
+in '0' even though all files start at line 1. Furthermore, versions
+earlier than 1.4.6 did not support the '__program__' macro. If you want
+'fatal_error' to work across the entire 1.4.x release series, a better
+implementation would be:
define(`fatal_error',
`errprint(ifdef(`__program__', `__program__', ``m4'')'dnl
fatal_error(`inside wrapped text')')
=>
^D
- error-->m4:stdin:6: Warning: excess arguments to builtin `divnum' ignored
+ error->m4:stdin:6: Warning: excess arguments to builtin `divnum' ignored
=>0
- error-->m4:stdin:6: fatal error: inside wrapped text
+ error->m4:stdin:6: fatal error: inside wrapped text
\1f
File: m4.info, Node: Copying This Package, Next: Copying This Manual, Prev: Answers, Up: Top
Version 3, 29 June 2007
- Copyright (C) 2007 Free Software Foundation, Inc. `http://fsf.org/'
+ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
The licenses for most software and other practical works are designed
to take away your freedom to share and change the works. By contrast,
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-also to any other work released this way by its authors. You can apply
-it to your programs, too.
+share and change all versions of a program--to make sure it remains free
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+GNU General Public License for most of our software; it applies also to
+any other work released this way by its authors. You can apply it to
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When we speak of free software, we are referring to freedom, not
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The Free Software Foundation may publish revised and/or new
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later version.
- 15. Disclaimer of Warranty.
+ 15. Disclaimer of Warranty.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE
SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
NECESSARY SERVICING, REPAIR OR CORRECTION.
- 16. Limitation of Liability.
+ 16. Limitation of Liability.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
- AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU
- FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
+ AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR
+ DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA
BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
THE POSSIBILITY OF SUCH DAMAGES.
- 17. Interpretation of Sections 15 and 16.
+ 17. Interpretation of Sections 15 and 16.
If the disclaimer of warranty and limitation of liability provided
above cannot be given local legal effect according to their terms,
connection with the Program, unless a warranty or assumption of
liability accompanies a copy of the Program in return for a fee.
-
END OF TERMS AND CONDITIONS
===========================
General Public License for more details.
You should have received a copy of the GNU General Public License
- along with this program. If not, see `http://www.gnu.org/licenses/'.
+ along with this program. If not, see <http://www.gnu.org/licenses/>.
Also add information on how to contact you by electronic and paper
mail.
notice like this when it starts in an interactive mode:
PROGRAM Copyright (C) YEAR NAME OF AUTHOR
- This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This program comes with ABSOLUTELY NO WARRANTY; for details type 'show w'.
This is free software, and you are welcome to redistribute it
- under certain conditions; type `show c' for details.
+ under certain conditions; type 'show c' for details.
- The hypothetical commands `show w' and `show c' should show the
+ The hypothetical commands 'show w' and 'show c' should show the
appropriate parts of the General Public License. Of course, your
program's commands might be different; for a GUI interface, you would
use an "about box".
You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. For more information on this, and how to apply and follow
-the GNU GPL, see `http://www.gnu.org/licenses/'.
+the GNU GPL, see <http://www.gnu.org/licenses/>.
The GNU General Public License does not permit incorporating your
program into proprietary programs. If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library. If this is what you want to do, use the
GNU Lesser General Public License instead of this License. But first,
-please read `http://www.gnu.org/philosophy/why-not-lgpl.html'.
-
-\1f
-File: m4.info, Node: Copying This Manual, Next: Indices, Prev: Copying This Package, Up: Top
-
-Appendix B How to make copies of this manual
-********************************************
-
-This appendix covers the license for copying this manual. Note that
-some of the longer examples in this manual are also distributed in the
-directory `m4-1.4.16/examples/', where a more permissive license is in
-effect when copying just the examples.
-
-* Menu:
-
-* GNU Free Documentation License:: License for copying this manual
+please read <http://www.gnu.org/philosophy/why-not-lgpl.html>.
projects / platform / upstream / m4.git / blobdiff