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.
Normally configure
scripts complain about
--with-package options that they do not support.
See Controlling Checking of configure
Options, for details, and for how to override the
defaults.
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.
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, dashes, plus signs, and dots.
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 named
with_package
, with any non-alphanumeric characters in
package changed into ‘_’. You may use that variable instead,
if you wish.
Note that action-if-not-given is not expanded until the point that
AC_ARG_WITH
was expanded. If you need the value of
with_package
set to a default value by the time argument
parsing is completed, use m4_divert_text
to the DEFAULTS
diversion (see m4_divert_text) (if done as an argument to
AC_ARG_WITH
, also provide non-diverted text to avoid a shell
syntax error).
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. The easiest way to provide the
proper leading whitespace is to format your help-string with the macro
AS_HELP_STRING
(see Making Your Help Strings Look Pretty).
The following example shows how to use the AC_ARG_WITH
macro in
a common situation. You want to let the user decide whether to enable
support for an external library (e.g., the readline library); if the user
specified neither --with-readline nor --without-readline,
you want to enable support for readline only if the library is available
on the system.
AC_ARG_WITH([readline], [AS_HELP_STRING([--with-readline], [support fancy command line editing @<:@default=check@:>@])], [], [: m4_divert_text([DEFAULTS], [with_readline=check])]) LIBREADLINE= AS_IF([test "x$with_readline" != xno], [AC_CHECK_LIB([readline], [main], [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) AC_DEFINE([HAVE_LIBREADLINE], [1], [Define if you have libreadline]) ], [if test "x$with_readline" != xcheck; then AC_MSG_FAILURE( [--with-readline was given, but test for readline failed]) fi ], -lncurses)])
The next example shows how to use AC_ARG_WITH
to give the user the
possibility to enable support for the readline library, in case it is still
experimental and not well tested, and is therefore disabled by default.
AC_ARG_WITH([readline], [AS_HELP_STRING([--with-readline], [enable experimental support for readline])], [], [with_readline=no]) LIBREADLINE= AS_IF([test "x$with_readline" != xno], [AC_CHECK_LIB([readline], [main], [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) AC_DEFINE([HAVE_LIBREADLINE], [1], [Define if you have libreadline]) ], [AC_MSG_FAILURE( [--with-readline was given, but test for readline failed])], [-lncurses])])
The last example shows how to use AC_ARG_WITH
to give the user the
possibility to disable support for the readline library, given that it is
an important feature and that it should be enabled by default.
AC_ARG_WITH([readline], [AS_HELP_STRING([--without-readline], [disable support for readline])], [], [with_readline=yes]) LIBREADLINE= AS_IF([test "x$with_readline" != xno], [AC_CHECK_LIB([readline], [main], [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) AC_DEFINE([HAVE_LIBREADLINE], [1], [Define if you have libreadline]) ], [AC_MSG_FAILURE( [readline test failed (--without-readline to disable)])], [-lncurses])])
These three examples can be easily adapted to the case where
AC_ARG_ENABLE
should be preferred to AC_ARG_WITH
(see
Choosing Package Options).