C:\test>start /b lsn.pl 25000

C:\test>Running with pid:12100

C:\test>lsn.pl 25000
Running with pid:11664
Only one usage of each socket address (protocol/network address/port) is normally permitted at C:\test\lsn.pl line 7.

C:\test>taskkill /f /pid 12100
SUCCESS: The process with PID 12100 has been terminated.

##</code><code>##

#! perl -slw
use strict;
use IO::Socket;

print "Running with pid:$$";

my $lsn = IO::Socket::INET->new(
    Listen => 1, LocalPort => $ARGV[0]
) or die $^E;

while( my $client = $lsn->accept ) {
    close $client;
}