On Unix systems you can use this:

use POSIX;

sub daemon {
   if($pid = fork) {
       # Parent
       exit 0;
   } elsif (defined $pid) {
       # Child
       setsid();     # detach session
       do_stuff();   # do some usefull stuff
   } else {
       die "Cannot fork: $!\n"; 
   }
}
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