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14.3 Choosing Package Options
If a software package has optional compile-time features, the user can
give `configure' command line options to specify whether to compile
them. The options have one of these forms:
These options allow users to choose which optional features to build
and install. `--enable-FEATURE' options should never make a feature
behave differently or cause one feature to replace another. They
should only cause parts of the program to be built rather than left out.
The user can give an argument by following the feature name with `='
and the argument. Giving an argument of `no' requests that the feature
_not_ be made available. A feature with an argument looks like
`--enable-debug=stabs'. If no argument is given, it defaults to `yes'.
`--disable-FEATURE' is equivalent to `--enable-FEATURE=no'.
Normally `configure' scripts complain about `--enable-PACKAGE'
options that they do not support. Note: Option Checking, for
details, and for how to override the defaults.
For each optional feature, `configure.ac' should call
`AC_ARG_ENABLE' to detect whether the `configure' user asked to include
it. Whether each feature is included or not by default, and which
arguments are valid, is up to you.
-- Macro: AC_ARG_ENABLE (FEATURE, HELP-STRING, [ACTION-IF-GIVEN],
If the user gave `configure' the option `--enable-FEATURE' or
`--disable-FEATURE', run shell commands ACTION-IF-GIVEN. If
neither option was given, run shell commands ACTION-IF-NOT-GIVEN.
The name FEATURE indicates an optional user-level facility. It
should consist only of alphanumeric characters, dashes, and dots.
The option's argument is available to the shell commands
ACTION-IF-GIVEN in the shell variable `enableval', which is
actually just the value of the shell variable named
`enable_FEATURE', with any non-alphanumeric characters in FEATURE
changed into `_'. You may use that variable instead, if you wish.
The HELP-STRING argument is like that of `AC_ARG_WITH' (*note
You should format your HELP-STRING with the macro `AS_HELP_STRING'
(Note: Pretty Help Strings).
See the examples suggested with the definition of `AC_ARG_WITH'
(Note: External Software) to get an idea of possible
applications of `AC_ARG_ENABLE'.
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