You probably want to split off the file writes into a child process:

use strict;

# Do lots of stuff

write_file();

sub write_file {

  if (defined (my $pid=fork)) {
    if ($pid) { 
      # Parent, let's just continue
      return;
    } else {
      # Child, do the file mod stuff.
      do_write_file();
      exit 0;
    }
  } else {
  die "Blerch: could not fork: $!\n";
  }
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Note that this code is quite unpolished (e.g. the if/else structure could be saner, and you definitely want to set a SIGCHLD handler in your parent to check the return value of the child), but it should get you on your way.

CU
Robartes-