The code is correct, but confusing with all the 'if not's. See RMGir's reply above for an explanation of what the code does. However, to make it less confusing, here's a fork()ing framework that uses straight ifs that are easier to understand (at least for me):

use strict;
if (defined(my $pid=fork()) {
  if ($pid) {
  # $pid is not 0, so this is the parent
  # Let's redirect the user (more extensive code in your example).
  redirect_user();
  } else {
  # $pid=0, so this is the child
  my $retval=do_child_code();
  exit $retval;
  }
} else {
# Oops, fork() returned undef - something is definitely wrong.
  DieNice("Unable to fork: $!\n");
}

sub do_child_code {

  # Do your time consuming stuff, setting $retval to
  # a useful number
  return $retval;
}
[download]

You could do without the else block calling do_child_code, and have the child just fall through down to the child code, but this way it's a lot easier to understand and maintain.

CU
Robartes-