17.1 Options generalities

Various features of Automake can be controlled by options. Except where noted otherwise, options can be specified in one of several ways. Most options can be applied on a per-Makefile basis when listed in a special Makefile variable named AUTOMAKE_OPTIONS. Some of these options only make sense when specified in the toplevel Makefile.am file. Options are applied globally to all processed Makefile files when listed in the first argument of AM_INIT_AUTOMAKE in configure.ac, and some options which require changes to the configure script can only be specified there. These are annotated below.

As a general rule, options specified in AUTOMAKE_OPTIONS take precedence over those specified in AM_INIT_AUTOMAKE, which in turn take precedence over those specified on the command line.

Also, some care must be taken about the interactions among strictness level and warning categories. As a general rule, strictness-implied warnings are overridden by those specified by explicit options. For example, even if ‘portability’ warnings are disabled by default in foreign strictness, an usage like this will end up enabling them:

AUTOMAKE_OPTIONS = -Wportability foreign

However, a strictness level specified in a higher-priority context will override all the explicit warnings specified in a lower-priority context. For example, if configure.ac contains:

AM_INIT_AUTOMAKE([-Wportability])

and Makefile.am contains:

AUTOMAKE_OPTIONS = foreign

then ‘portability’ warnings will be disabled in Makefile.am.