#! perl -slw
use strict;
use Win32::Semaphore;

( my $semName = $0 ) =~s[\\][/]g;
die 'Program already running' if Win32::Semaphore->open( $semName );
my $sem = Win32::Semaphore->new( 1, 1, $semName ) or die $^E;
sleep 1000;
__END__
c:\test>start /b loner.pl

c:\test>loner.pl
Program already running at c:\test\loner.pl line 6.