Not all platforms automatically reinstall their (native) signal handlers after a signal delivery. This means that the handler works only the first time the signal is sent. The solution to this problem is to use "POSIX" signal handlers if available, their behaviour is well-defined.

So to rework your example with the one from perlipc:

!/usr/bin/perl -w

use POSIX ();
use FindBin ();
use File::Basename ();
use File::Spec::Functions;

$|=1;

# make the daemon cross-platform, so exec always calls the script
# itself with the right path, no matter how the script was invoked.

my $script = File::Basename::basename($0);
my $SELF = catfile $FindBin::Bin, $script;

# POSIX unmasks the sigprocmask properly
my $sigset = POSIX::SigSet->new();
my $action = POSIX::SigAction->new('sigHUP_handler',
                                   $sigset,
                                   &POSIX::SA_NODEFER);
POSIX::sigaction(&POSIX::SIGINT, $action);

sub sigHUP_handler {
  print "got SIGINT\n";
  exec($SELF) or die "Couldn't restart: $!\n";
}

code();

sub code {
  my $c = 0;
  while (++$c) {
    sleep 2;
    print "$$ - $c\n";
  }
}
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#!/usr/bin/perl

use POSIX();

$|=1;

$sub = sub { exec "$0" };

# POSIX unmasks the sigprocmask properly
my $sigset = POSIX::SigSet->new();
my $action = POSIX::SigAction->new( 
                     $sub, $sigset, &POSIX::SA_NODEFER );
POSIX::sigaction(&POSIX::SIGINT, $action);

print (++$counter), sleep 1 while 1
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