sub munge {
    my ($str, $pat, $repl) = @_;

    while ($str =~ /$pat/g) {
        my $temp = $repl;
        for (1..$#+) {
            while ( (my $x = index $temp, "\$$_") >= 0) {
                substr ($temp, $x, length($_)+1) = $$_;
            }
        }
        my $pos = pos $str;
        my $offset = $+[$#+]-$-[0];
        substr($str, $pos-$offset, $offset) = $temp;
        pos($str) = $pos - $offset + length($temp);
    }

    return $str;
}

# Here's an example:
print "#";
print munge('aaaababbaabbbbabab', '(a)(b+)', ' $2*$1 ');
print "#";