12.1 Working With External Software

Some packages require, or can optionally use, other software packages that are already installed. The user can give configure command line options to specify which such external software to use. The options have one of these forms:

--with-package[=arg] --without-package

For example, `--with-gnu-ld' means work with the GNU linker instead of some other linker. `--with-x' means work with The X Window System.

The user can give an argument by following the package name with `=' and the argument. Giving an argument of `no' is for packages that are used by default; it says to not use the package. An argument that is neither `yes' nor `no' could include a name or number of a version of the other package, to specify more precisely which other package this program is supposed to work with. If no argument is given, it defaults to `yes'. `--without-package' is equivalent to `--with-package=no'.

configure scripts do not complain about `--with-package' options that they do not support. This behavior permits configuring a source tree containing multiple packages with a top-level configure script when the packages support different options, without spurious error messages about options that some of the packages support. An unfortunate side effect is that option spelling errors are not diagnosed. No better approach to this problem has been suggested so far.

For each external software package that may be used, `configure.ac' should call AC_ARG_WITH to detect whether the configure user asked to use it. Whether each package is used or not by default, and which arguments are valid, is up to you.

Macro: AC_ARG_WITH (package, help-string, [action-if-given], [action-if-not-given])

If the user gave configure the option `--with-package' or `--without-package', run shell commands action-if-given. If neither option was given, run shell commands action-if-not-given. The name package indicates another software package that this program should work with. It should consist only of alphanumeric characters and dashes.

The option's argument is available to the shell commands action-if-given in the shell variable withval, which is actually just the value of the shell variable with_package, with any `-' characters changed into `_'. You may use that variable instead, if you wish.

The argument help-string is a description of the option that looks like this:

--with-readline support fancy command line editing

help-string may be more than one line long, if more detail is needed. Just make sure the columns line up in `configure --help'. Avoid tabs in the help string. You'll need to enclose the help string in `[' and `]' in order to produce the leading spaces.

You should format your help-string with the macro AC_HELP_STRING (see section 12.3 Making Your Help Strings Look Pretty).

Macro: AC_WITH (package, action-if-given, [action-if-not-given])

This is an obsolete version of AC_ARG_WITH that does not support providing a help string.