Use an array (or a hash). What you're trying to do now smells like symbolic refrences, which are just yicky (to use the technical term ) and make your code harder to write and maintain.

You will also need to use the /e modifier (which causes Perl to eval the right-side as an expression).

use strict;
my @red;
$red[1]='black';
$red[2]='red';
$line =~ s/\$red(\d)/$red[$1]/ge;
[download]