What are Makefile.am and Makefile.in?

Question

These two files are mostly seen in open source projects.

What are they for, and how do they work?

Answer 1

Makefile.am is a programmer-defined file and is used by automake to generate the Makefile.in file (the .am stands for automake). The configure script typically seen in source tarballs will use the Makefile.in to generate a Makefile.

The configure script itself is generated from a programmer-defined file named either configure.ac or configure.in (deprecated). I prefer .ac (for autoconf) since it differentiates it from the generated Makefile.in files and that way I can have rules such as make dist-clean which runs rm -f *.in. Since it is a generated file, it is not typically stored in a revision system such as Git, SVN, Mercurial or CVS, rather the .ac file would be.

Read more on GNU Autotools. Read about make and Makefile first, then learn about automake, autoconf, libtool, etc.

Answer 2

Simple example

Shamelessly adapted from: http://www.gnu.org/software/automake/manual/html_node/Creating-amhello.html and tested on Ubuntu 14.04 Automake 1.14.1.

Makefile.am

SUBDIRS = src dist_doc_DATA = README.md 

README.md

Some doc. 

configure.ac

AC_INIT([automake_hello_world], [1.0], [[email protected]]) AM_INIT_AUTOMAKE([-Wall -Werror foreign]) AC_PROG_CC AC_CONFIG_HEADERS([config.h]) AC_CONFIG_FILES([  Makefile  src/Makefile ]) AC_OUTPUT 

src/Makefile.am

bin_PROGRAMS = autotools_hello_world autotools_hello_world_SOURCES = main.c 

src/main.c

#include <config.h> #include <stdio.h>  int main (void) {   puts ("Hello world from " PACKAGE_STRING);   return 0; } 

Usage

autoreconf --install mkdir build cd build ../configure make sudo make install autotools_hello_world sudo make uninstall 

This outputs:

Hello world from automake_hello_world 1.0 

Notes

• autoreconf --install generates several template files which should be tracked by Git, including Makefile.in. It only needs to be run the first time.

• make install installs:

  • the binary to /usr/local/bin
  • README.md to /usr/local/share/doc/automake_hello_world

On GitHub for you to try it out.