GNU macro processor

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 Franc,ois Pinard and other volunteers on the Internet. All names and email addresses can be found in the file `THANKS' from the GNU m4 distribution.

This is release 1.4.2. It is now to be considered stable, future releases 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. So, it might go away, do not count on it yet.


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		Conditionals and loops

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 UNIX commands		Macros for running UNIX commands
13. Miscellaneous builtin macros
14. Fast loading of frozen states

15. Compatibility with other versions of `m4`		Compatibility with other versions of m4
Concept index		Index for many concepts
Macro index		Index for all m4 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1.2 Historical references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 Other tokens		Other kinds of input tokens
2.4 Comments		Comments in m4 input

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 UNIX commands

12.1 Executing simple commands
12.2 Reading the output of commands
12.3 Exit codes
12.4 Making names for temporary files

Miscellaneous builtin macros

13.1 Printing error messages
13.2 Exiting from `m4`		Exiting from m4

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

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