3.1 Macro Format

Each macro in the Archive has an all-upper-case name with the prefix AX_. The macro is stored in a file with the same name, in lower case, and with the suffix .m4. Unless absolutely necessary, the file contents should be in ASCII. For example, use apostrophe (U+27) for quoting identifiers instead of Unicode quotation mark characters U+2018, U+2019.

The file should begin with a header comment containing three named sections: synopsis, description, and license.

The synopsis gives a summary of the macro usage and arguments. In this section, square brackets ([]) are used to indicate optional parameters, and may be nested.

The description contains a prose description of the macro. It should describe the function of the macro, and the meaning of any arguments given in the synopsis. The description should also identify:

• any default macro parameter values
• any new --with or --enable options, and their default values
• any argument variables consulted (AC_ARG_VAR)
• any substituted variables (AC_SUBST)
• any defined precompiler constants (AC_DEFINE)

Macros should be defined with AC_DEFUN, using correct quoting. Comments should be used liberally within the macro, with dnl used for comments at the m4sh level and # used for comments at the shell level.

If a macro is renamed, the AU_ALIAS macro should be used to guide users of the old name to the new name:

AU_ALIAS([OLD_NAME], [AX_NEW_NAME])

3.2 Submitting Macros

To submit updates to the Autoconf Archive, please create an issue in the patch tracker and attach a (preferably git-format-patch(1)-formatted) patch file. Users of github.com may prefer to create a pull request for the Autoconf Archive Mirror at Github. Please make sure your submission contains the following items:

• a synopsis that shows how the macro must be be called,
• a brief description of the macro’s purpose,
• the list of authors (optionally with e-mail addresses),
• licensing terms, and
• the m4 source code.

Macros can be submitted under any GPL-compatible free software license. The Free Software Foundation, however, recommends use of the all-permissive license for Autoconf macros.

3.3 Writing Highly Usable Macros

Autoconf macros are used in a surprising variety of ways, and a well-written macro should be flexible enough to suit all of these uses.

See the Autotools Mythbuster for suggestions on how to write well-encapsulated, portable macros.