#!/usr/bin/perl -w

use strict;
use Net::SSH::Perl;

my $rcmd = "
        perl -e 'use strict; open(FD, filetochange.txt) or die \"can not open FD: $!\";
        while (<FD>) {
                if (/mon/ &&  /messages/) {
                        print $_;
                        #change line here
                }
        }
        close(FD);
'";


my $ssh = Net::SSH::Perl->new('localhost', protocol=>('2,1'));

$ssh->login('joe1','blabla');

my($stdout, $stderr, $exit) = $ssh->cmd("$rcmd");

print $stdout;