GNU M4

This manual is for GNU M4 (version 1.4.6, 24 August 2006), a package containing an implementation of the m4 macro language.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software 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."

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.

GNU m4 was originally written by René Seindal, with subsequent changes by François Pinard and other volunteers on the Internet. All names and email addresses can be found in the files `AUTHORS' and `THANKS' from the GNU M4 distribution.

This is release 1.4.6. 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:

./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.


1. Introduction and preliminaries
2. Lexical and syntactic conventions
3. How to invoke macros
4. How to define new macros
5. Conditionals, loops, and recursion

6. How to debug macros and input

7. Input control
8. File inclusion
9. Diverting and undiverting output

10. Macros for text handling
11. Macros for doing arithmetic
12. Running shell commands		Macros for running shell commands
13. Miscellaneous builtin macros
14. Fast loading of frozen state

15. Compatibility with other versions of `m4`		Compatibility with other versions of m4
16. Correct version of some examples
A. Copying This Manual		How to make copies of this manual
B. Indices		Indices of concepts and macros
--- The Detailed Node Listing --- Introduction and preliminaries
1.1 Introduction to `m4`
1.2 Historical references
1.3 Invoking `m4`
1.4 Problems and bugs
1.5 Using this manual
Lexical and syntactic conventions
2.1 Names		Macro names
2.2 Quoted strings		Quoting input to m4
2.3 Comments		Comments in m4 input
2.4 Other tokens		Other kinds of input tokens
2.5 Input Processing		How m4 copies input to output
How to invoke macros
3.1 Macro invocation
3.2 Preventing macro invocation
3.3 Macro arguments
3.4 Quoting macro arguments		On Quoting Arguments to macros
3.5 Macro expansion		Expanding macros
How to define new macros
4.1 Defining a macro		Defining a new macro
4.2 Arguments to macros
4.3 Special arguments to macros		Pseudo arguments to macros
4.4 Deleting a macro
4.5 Renaming macros
4.6 Temporarily redefining macros

4.7 Indirect call of macros
4.8 Indirect call of builtins
Conditionals, loops, and recursion
5.1 Testing macro definitions		Testing if a macro is defined
5.2 Comparing strings		If-else construct, or multibranch
5.3 Loops and recursion		Loops and recursion in m4
How to debug macros and input
6.1 Displaying macro definitions
6.2 Tracing macro calls
6.3 Controlling debugging output
6.4 Saving debugging output
Input control
7.1 Deleting whitespace in input
7.2 Changing the quote characters
7.3 Changing comment delimiters		Changing the comment delimiters
7.4 Changing the lexical structure of words
7.5 Saving input		Saving input until end of input
File inclusion
8.1 Including named files
8.2 Searching for include files
Diverting and undiverting output
9.1 Diverting output
9.2 Undiverting output
9.3 Diversion numbers
9.4 Discarding diverted text
Macros for text handling
10.1 Calculating length of strings
10.2 Searching for substrings
10.3 Searching for regular expressions
10.4 Extracting substrings
10.5 Translating characters
10.6 Substituting text by regular expression
10.7 Formatted output		Formatting strings (printf-like)
Macros for doing arithmetic
11.1 Decrement and increment operators
11.2 Evaluating integer expressions
Running shell commands
12.1 Determining the platform
12.2 Executing simple commands
12.3 Reading the output of commands
12.4 Exit status
12.5 Making names for temporary files
Miscellaneous builtin macros
13.1 Printing error messages
13.2 Printing current location
13.3 Exiting from `m4`		Exiting from m4
Fast loading of frozen state
14.1 Using frozen files
14.2 Frozen file format
Compatibility with other versions of `m4`
15.1 Extensions in GNU `m4`		Extensions in GNU M4
15.2 Facilities in System V `m4` not in GNU `m4`		Facilities in System V m4 not in GNU M4
15.3 Other incompatibilities
Copying This Manual
A.1 GNU Free Documentation License		License for copying this manual
Indices
B.1 Concept index		Index for many concepts
B.2 Macro index		Index for all m4 macros

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