I needed to something similar. AS the other post mentions Proc::Background did the trick. Here is the sample code. I wanted to listen on specific ports and then run an nmap scan from external host to see if the ports are reachable. This was part of a larger tool.

#!/bin/perl -w

use strict;
use warnings;

use Proc::Background;
use Net::OpenSSH;



    my @ports = ("443","8080");
    my @threads = '';
    my $index = 0;
    foreach my $port(@ports){

        $threads[$index] = Proc::Background->new("/usr/bin/perl thread
+.pl $port");    
        $index++;
    }


    my $ssh = Net::OpenSSH->new("remote.host.net", user=>"me",passwd=>
+"******");
    $ssh->error and die "Can't ssh to host\n";

    my @output = $ssh->capture("nmap -p T:8080,443 my.host.name");

    print @output;

    foreach my $thread (@threads){
        print "Killing $thread\n";
        $thread->die;
    }
    print "Done ";
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