aclocal

aclocal is a script in the GNU Autotools suite that generates or updates a local macro definitions file named aclocal.m4. It collects macro definitions from installed macro packages and any project-specific macros so that configure scripts can use the macros defined by those packages.

Aclocal searches standard macro directories such as /usr/share/aclocal and other site-wide locations, as well as any m4 directory within the project. The resulting aclocal.m4 contains the definitions of macros available to autoconf, enabling macros used in configure.ac to be expanded correctly. The search path can be augmented with the ACLOCAL_PATH environment variable or with the -I option to aclocal.

Aclocal is typically invoked as part of the autotools workflow, most commonly through autoreconf -i, which regenerates aclocal.m4 along with other autotools-generated files. It can also be run directly, for example aclocal -I m4, to update aclocal.m4 so that macros from a local directory are included before proceeding with the rest of the autotools steps.

The tool supports integration with other Autotools components such as automake and libtool, and helps ensure that a project has access to the necessary macros without depending solely on system-wide installations. This contributes to more portable builds across different environments and distributions, by capturing the required macro definitions locally within the project.