#!/usr/bin/perl --

use strict;
use warnings;

use threads;
use threads::shared;

Main(@ARGV);
exit(0);

sub Main {
  local $SIG{'HUP'} = 'switchFlag';
  share($::flag);
  $::flag = !!undef;    # false

  my $thr = threads->new( \&printer );
  $thr->detach();
  sleep 10000;
  print threads->tid, " is here\n";
} ## end sub Main

sub printer {
  while (1) {
    sleep 1;
    print threads->tid, " Shared: $::flag\n";
  }
} ## end sub printer

sub switchFlag {
  $::flag = !$::flag;
  print threads->tid, " caught signal\n";
  $SIG{'HUP'} = 'switchFlag';
}
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Nice one...Output from my box... 0 caught signal 0 is here ;-)