You need to quote macro names which you want Autoconf to pass through to the configure script without expanding. You should also quote a word that looks as if it may be a macro, in case a macro of that name is added at a later date. kAre they actually forbidden?) You must quote that text whether it is passed as a macro argument or not.
The macros that Autoconf makes available begin with ‘AC_’,
‘AU_’, ‘AH_’, ‘AS_’ or ‘m4_’. The names of macros
that Automake makes available begin with ‘AM_’. (There are also a
handful of others that don’t follow this pattern:
others not following this pattern:
For example, in order for the following to appear in configure
echo "Hard rock was here! --AC_DC"
you need to quote the ‘AC_DC’ part, to protect your script in case
Autoconf ever adds a macro
This will be achieved with either of these two approaches in
(quoting just the potential problems, or quoting the entire line):
echo "Hard rock was here! --[AC_DC]" [echo "Hard rock was here! --AC_DC"]
When you use the same text in a macro argument, you must have an extra quotation level (since one is stripped away by the macro substitution), either around just the problematic portions, or over the entire argument:
AC_MSG_WARN([[AC_DC] stinks --Iron Maiden]) AC_MSG_WARN([[AC_DC stinks --Iron Maiden]])
In general, then, it is a good idea to use double quoting for all literal string arguments.
To be really safe,
autoconf warning about a possibly
because it collides
with the namespace of macros reserved for the Autoconf language.
To achieve this, you can
either use creative shell constructs,
or use a quadrigraph:
echo "Hard rock was here! --AC""_DC" AC_MSG_WARN([[AC@&t@_DC stinks --Iron Maiden]])
If you need to pass through a macro name to the produced
configure script, you need to use
quote the occurence of the name, thus:
m4_pattern_allow([dnl]) echo fun fact: [dnl] stands for Discard to Next Line
dnl is a built-in M4 macro that leads to the rest of the line
being discarded, so the following line in configure.ac
echo fun fact: dnl stands for Discard to Next Line
will lead to the following being output when
configure is run: