#!/usr/bin/perl -w

$regex = "s/foo/bar/g";
$compiled = qr/$regex/;   # program works the same 
                          # whether I do this or not

$string = "foo fru foodyfoo";

$string =~ $compiled;
print "$string\n";      # no substitution! $string is still
                        # "foo fru foodyfoo" instead of
                        # "bar fru bardybar".