5.3 Input files for projects with subdirectories

For simple projects that distribute all files in the same directory it is enough to have a single Makefile.am that builds everything in place.

In larger projects, it is common to organize files in different directories, in a tree. For example, there could be a directory for the program’s source, one for the testsuite, and one for the documentation; or, for very large projects, there could be one directory per program, per library or per module.

One approach is to build these subdirectories recursively, employing make recursion: each directory contains its own Makefile.am. The top-level directory has its own Makefile.am as well as a configure.ac that is used for all subdirectories. When make is run from the top-level directory, it enters each subdirectory in turn, and invokes there a new make instance to build the directory’s contents.

However, it is worth nothing that the use of make recursion has issues and drawbacks, and that it’s certainly possible to have packages with a multi-directory layout that make little or no use of such recursion (examples of such packages are GNU Bison and GNU Automake itself); see the Alternative section below.