Autoconf generates shell scripts that probe the host system for compilers, headers, and libraries — producing a `config.h` and Makefiles that build on Linux, BSDBerkeley Software Distribution — a family of Unix-like operating systems originating from UC Berkeley., and Solaris alike. It paired with Automake and Libtool as the GNU build triad for decades. Example: `./configure --prefix=/usr/local && make && make install` adapts to whatever the machine provides.

Autoconf ended hand-editing dozens of `-D` compiler flags for every UnixAn influential multitasking OS from the 1970s — files, pipes, and C shaped Linux, macOS, and BSD. variant.

It became the standard way open-source C projects achieved portable builds before CMake dominated.