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

my $prompt = "Enter the start date (mm/dd/yyyy hh:mm): ";

my $line;
while ( (print "$prompt"), $line =<STDIN>)
{
   next if $line =~ /^\s*$/; #simple reprompt on blank line
   
   my ($month, $day, $year, $hour, $minute) = 
       $line =~ m|^\s*(\d+)/(\d+)/(\d+)\s+(\d+):(\d+)\s*$|;
       
   if (!defined $minute) #regex failed initial "laugh test"
   {
      print "illegal format!\n";
      next;
   }
   
   if ($month <1 or $month>12)
   {
      print "got month of $month - must be 1-12\n";
      next;
   }
   
   if ($day <1 or $day>31)
   {
      print "got day of $day - must be 1-31\n";
      next; 
   }

   # more conditions here
   
   #finally try to convert the date to an epoch and see
   #if that works, eg  2/31/2012 should fail... 
   
   #all tests pass, you have a "good date time"

}
__END__
C:\TEMP>commandloop5.pl
Enter the start date (mm/dd/yyyy hh:mm): fjfjf 97609876 afadfa
illegal format!
Enter the start date (mm/dd/yyyy hh:mm): 0/0/2012 99:00
got month of 0 - must be 1-12
Enter the start date (mm/dd/yyyy hh:mm): 1/0/2012 99:00
got day of 0 - must be 1-31
Enter the start date (mm/dd/yyyy hh:mm): I stopped program