You can do it using the register_handler function that Net::SSH::Perl provides.

For example

#!/usr/bin/perl -w

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

my $host = "localhost";
my $username = "anthski";
my $password = "somepassword";

my $ssh = Net::SSH::Perl->new($host, debug => 0, protocol => '2');

my $command = "tail -f /var/log/messages";
my $loginStatus = $ssh->login($username,$password);

my $stdout;
my $stderr;
my $exit;

$ssh->register_handler("stdout", sub {
        # This will match any packets which are stdout and print them 
+to the screen
        # You could do something smarter with them if you wanted
        my($channel, $buffer) = @_;
        my $str = $buffer->bytes;
        print "$str\n";
});

($stdout,$stderr,$exit) = $ssh->cmd($command);
[download]

As per my comment in the code, you can then do whatever you want with the output of your command.

cheers,
Anth