#!/usr/bin/perl 
 
# This is a script that will increment time by 30 minutes. 
 
use strict; 
use warnings; 
use POSIX qw/strftime/; 
 
 
my $Start = "17/12/2012 00:00:00"; 
my $End = "20/12/2012 23:00:00"; 
my $Now = $Start; 
 
while($Now > $End){ 
 
  $Now = Some code that will add 30 minutes. 
  
}

#!/usr/bin/perl 
 
use v5.10.1; 
use strict; 
use warnings; 
use POSIX qw(strftime); 
use Date::Calc qw(Mktime); 
use Data::Dumper; 
 
my $start = '17/12/2012 00:30:00'; 
my ($day,$mon,$yr,$hr,$min,$sec) = split(/[\/ :]/, $start); 
 
my $time = Mktime($yr,$mon,$day, $hr,$min,$sec); 
 
for (1..10) { 
    say scalar localtime($time); 
    $time += 60*30; 
}