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Automake includes a number of Autoconf macros which can be used in
your package (see Autoconf macros supplied with Automake); some of them are actually required by
Automake in certain situations. These macros must be defined in your
aclocal.m4; otherwise they will not be seen by
autoconf.
The aclocal program will automatically generate
aclocal.m4 files based on the contents of configure.ac.
This provides a convenient way to get Automake-provided macros,
without having to search around. The aclocal mechanism
allows other packages to supply their own macros (see Writing your own aclocal macros). You can also use it to maintain your own set of custom
macros (see Handling Local Macros).
At startup, aclocal scans all the .m4 files it can
find, looking for macro definitions (see Macro search path). Then
it scans configure.ac. Any mention of one of the macros found
in the first step causes that macro, and any macros it in turn
requires, to be put into aclocal.m4.
Putting the file that contains the macro definition into
aclocal.m4 is usually done by copying the entire text of this
file, including unused macro definitions as well as both ‘#’ and
‘dnl’ comments. If you want to make a comment which will be
completely ignored by aclocal, use ‘##’ as the comment
leader.
When aclocal detects that the file containing the macro
definition is in a subdirectory of your package, it will use
m4_include instead of copying it; this makes the package
smaller and eases dependency tracking. This only works if the
subdirectory containing the macro was specified as a relative search
path with aclocal’s -I argument. (see Handling Local Macros for an example.) Any macro which is found in a system-wide
directory, or via an absolute search path will be copied.
The contents of acinclude.m4, if it exists, are also automatically included in aclocal.m4. We recommend against using acinclude.m4 in new packages (see Handling Local Macros).
While computing aclocal.m4, aclocal runs autom4te
(see Using Autom4te in The
Autoconf Manual) in order to trace the macros which are really used,
and omit from aclocal.m4 all macros which are mentioned but
otherwise unexpanded (this can happen when a macro is called
conditionally). autom4te is expected to be in the PATH,
just as autoconf. Its location can be overridden using the
AUTOM4TE environment variable.
Next: aclocal options, Previous: Other things Automake recognizes, Up: Scanning configure.ac [Contents][Index]