#!/usr/bin/perl -w

use strict;
use English;

open(my $config_file, '<', 'configure.ac')
    or die "cannot open configure.ac: $!";

my $version = '';
my $found_init = 0;
while (<$config_file>)
{
  if(/^AC_INIT\(GNU Emacs,\s*(\d+\.\d+(\.\d+)?)\s*\,.*/o)
  {
    $found_init and die 'found duplicate AC_INIT() in configure.ac';
    $version = $1;
    $found_init = 1;
  }
}

$found_init or die 'no AC_INIT() found in configure.ac';
print "$version\n";