#!/usr/bin/perl -w
use strict;

my $start = time;    # let's see what time it is

our $gap ||= 1;      # how many seconds between prints

while (1) {          # and from now on
  local $|   = 1;
  my    $now = time;    # see what time it is now

  my ( $sec, $min, $hour ) = ( $now - $start, 0, 0 ); # seconds passed

  while ( $sec > 3600 ) { $sec -= 3600; $hour++ }     # hours
  while ( $sec > 60   ) { $sec -= 60  ; $min++ }      # minutes

  printf ("\r%02d:%02d:%02d",$hour,$min,$sec);        # print time
  sleep($gap);                                        # wait a while
}