%hash = (1=>2
2 =>3
3 =>4);

$hash{2} = 5;
$hash = 6;
%hash = reverse(%hash);

for ($i = 1; $i < 5; $i++)
{
delete($hash{$1});
}
print(%hash)

#!/usr/bin/perl

use strict;
use warnings;

my %hash = (1=>2
  ,2 =>3
  ,3 =>4);

$hash{2} = 5;
my($hash) = 6;
%hash = reverse(%hash);

for (my($i) = 1; $i < 5; $i++)
   {
  delete($hash{$1});
   };
print(%hash)

$str =~m/\s+         # one or more whitespaces
                        $1         # from the first regex (the first "cache"d result)
                        .           # any "sign", letter, digit or what ever
                        in          # the word "in" (it's literal)
                        \s          # one whitespace
                        a           # the letter "a"
                        \s          # one whitespace
                       [a-d]{1}  # one letter (a, b, c or d)
                       (\w{2})   # two alphanumerical signs and save these two signs in $1
/x;