#!/usr/bin/perl
use strict;
use warnings;

our $foo;

sub do_something {
  $foo++;
  print "$foo\n";
}

our $running;
if (!$running) {
  $foo = 0;
  $running = 1;
  $SIG{INT} = sub {do $0};
  for (;;) {
    sleep (1);
    do_something();
  }
}