in reply to shell execution question

Sometimes solving a problem is only fixing a symptom. If you are really wanting to automate some commands via ssh, you really should look into btrott's Net::SSH::Perl. Here's an example: 
use strict;
use warnings;
use Net::SSH::Perl;

my $user = '';
my $pass = '';
my @host = qw(host1 host2);

for my $host (@host) {
   my $ssh = Net::SSH::Perl->new($host, protocol => "2,1");
   $ssh->login($user,$pass);
   
   my ($stdout, $stderr, $exit) = $ssh->cmd('hostname');
   print STDOUT $stdout if $stdout;
   print STDERR $stderr if $stderr;
   print "remote command exited with [$exit]\n";
}

[download]
I don't think you need to ping each host first, but should you still want to, check out Net::Ping.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

In Section Seekers of Perl Wisdom