I'm afraid you will have to test the value of $^O and load some OS specific modules or define some subroutines. I can't comment on the Unix side, but you might end up with something like:

BEGIN {
  if ($^O eq 'MSWin32') {
    eval <<'*END*';
      use Win32::Daemon::Simple 
        Service => 'SERVICENAME',
        Name => 'SERVICE NAME',
        Version => 'x.x',
        Info => {
          display =>  'SERVICEDISPLAYNAME',
          description => 'SERVICEDESCRIPTION',
        },
        Params => {};
*END*
    die $@ if $@;
  } else {
    eval <<'*END*';
      # do whatever you need to make it a daemon under Unix

      sub DoEvents {
        # check the value of the variable you set in $SIG{...} handler
+s 
        # and stop if asked to
      }
*END*
    die $@ if $@;
  }
}

while (1) {
  # do something
  sleep(60);
  DoEvents();
}
__END__
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Jenda
Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.
   -- Rick Osborne

Edit by castaway: Closed small tag in signature