automake-1.16: aclocal Invocation
6.3 Auto-generating aclocal.m4
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Automake includes a number of Autoconf macros that can be used in your
package (⇒Macros); some of them are 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
(⇒Extending aclocal). You can also use it to maintain your own
set of custom macros (⇒Local Macros).
At startup, ‘aclocal’ scans all the ‘.m4’ files it can find, looking
for macro definitions (⇒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 that will be completely ignored
by ‘aclocal’, use ‘##’ as the comment leader.
When a file selected by ‘aclocal’ is located in a subdirectory
specified as a relative search path with ‘aclocal’’s ‘-I’ argument,
‘aclocal’ assumes the file belongs to the package and uses ‘m4_include’
instead of copying it into ‘aclocal.m4’. This makes the package
smaller, eases dependency tracking, and cause the file to be distributed
automatically. (⇒Local Macros, for an example.) Any macro that
is found in a system-wide directory or via an absolute search path will
be copied. So use ‘-I `pwd`/reldir’ instead of ‘-I reldir’ whenever
some relative directory should be considered outside the package.
The contents of ‘acinclude.m4’, if this file exists, are also
automatically included in ‘aclocal.m4’. We recommend against using
‘acinclude.m4’ in new packages (⇒Local Macros).
While computing ‘aclocal.m4’, ‘aclocal’ runs ‘autom4te’ (⇒Using
‘Autom4te’ (autoconf)Using autom4te.) in order to trace the macros that
are used, and omit from ‘aclocal.m4’ all macros that 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.
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