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Properly formatting the `help strings' which are used in
AC_ARG_WITH
(see External Software) and AC_ARG_ENABLE
(see Package Options) can be challenging. Specifically, you want
your own `help strings' to line up in the appropriate columns of
`configure --help' just like the standard Autoconf `help
strings' do. This is the purpose of the AS_HELP_STRING
macro.
Expands into an help string that looks pretty when the user executes `configure --help'. It is typically used in
AC_ARG_WITH
(see External Software) orAC_ARG_ENABLE
(see Package Options). The following example makes this clearer.AC_ARG_WITH([foo], [AS_HELP_STRING([--with-foo], [use foo (default is no)])], [use_foo=$withval], [use_foo=no])The second argument of
AS_HELP_STRING
is not a literal, and should not be double quoted. See Autoconf Language, for a more detailed explanation. Then the last few lines of `configure --help' appear like this:--enable and --with options recognized: --with-foo use foo (default is no)The
AS_HELP_STRING
macro is particularly helpful when the left-hand-side and/or right-hand-side are composed of macro arguments, as shown in the following example.AC_DEFUN([MY_ARG_WITH], [AC_ARG_WITH([$1], [AS_HELP_STRING([--with-$1], [use $1 (default is $2)])], [use_[]$1=$withval], [use_[]$1=$2])])