#!/usr/bin/perl -w
use strict;

while (<DATA>) {
    next unless /^\s*s\//;    # Minimal checking
    chomp;
    my ($pat, $repl) = (split '/') [1, 2];
    my $s = "foo";
    eval "\$s =~ s/$pat/$repl/";
    warn "Warning: $@" if $@;
    print "$s\n";
}

__DATA__
s/foo/bar/
s/(fo)o/bar$1/