#!/usr/bin/perl

use strict;

my $find = '(<!--\s*<control_link_address>push1\.mycompany\.com</control_link_address>\s*-->)';
my $rplc = '$1\n <control_link_address>mdp.travel.co.uk</control_link_address>\n';

open( IN, "<", "/tmp/ls.conf" ) or die "/tmp/ls.conf: $!";
$/ = undef;
$_ = <IN>;
eval "s{$find}{$rplc}";
open( OUT, ">", "/tmp/ls.conf.new" ) or die "/tmp/ls.conf.new: $!";
print OUT;