27.1.1 Background: distributed generated files

Packages made with Autoconf and Automake ship with some generated files like ‘configure’ or ‘Makefile.in’. These files were generated on the developer's host and are distributed so that end-users do not have to install the maintainer tools required to rebuild them. Other generated files like Lex scanners, Yacc parsers, or Info documentation, are usually distributed on similar grounds.

Automake outputs rules in ‘Makefile’s to rebuild these files. For instance, make will run autoconf to rebuild ‘configure’ whenever ‘configure.ac’ is changed. This makes development safer by ensuring a ‘configure’ is never out-of-date with respect to ‘configure.ac’.

As generated files shipped in packages are up-to-date, and because tar preserves times-tamps, these rebuild rules are not triggered when a user unpacks and builds a package.