Re: M4 syntax $11 vs. ${11}

[Paul Eggert]

Eric Blake <address@hidden> writes:

> +fatal "need GNU m4 1.4.5 or later: $m4"
> +  unless system "echo 'ifdef(mac,bug)dnl' | $m4 --trace=mac 2>&1 | grep bug 
> >/dev/null";
> +
> +# Detect if we can use feature added in M4 1.4.9 to warn user about $10.
> +# Override the user's choice of --warn-macro-sequence, since the default
> +# macro sequence rejects ${1} even though we guarantee it is safe.
> +$m4 .= " --warn-macro-sequence='\\\$\\([0-9][0-9]+\\|{{\\)'"
> +  if ! system "$m4 --help | grep warn-macro-sequence >/dev/null";

Can you please rewrite this so that it invokes m4 once instead of
twice, and doesn't use grep at all?  You can use Perl's pattern
matching instead of grep.  And I think you can test for both features
by a single call to 'm4'.  This will help autom4te start up a bit
faster.

Perhaps it would be even better to test for these things at
configure-time: that way, we won't have to invoke 'm4' at all, at
run-time.

A nit: the "+" isn't needed.  Once you see two digits, you don't need
to look for more.