Makefile.PL

#!/usr/bin/perl -w

use strict;
use warnings;
use Config;
use File::Copy;

my $old = 'Makefile.in';
my $new = 'Makefile';

open OLD, "<", $old or die "Unable to open $old: $!\n";
open NEW, ">", $new or die "Unable to open $new: $!\n";
my $flag;
while (<OLD>) {
    if ($flag) {
        print NEW;
        next;
    } elsif (/^PERL\s*=\s*/) {
        print NEW "PERL = $Config{perlpath}\n";
    } else {
        print NEW;
    }
}

close OLD;
close NEW;