#!/usr/bin/perl

use warnings;
use strict;

use Data::Dumper;

{
        my %hash = ( 1 => 5, 3 => 12, 7 => 19, 9 => 44 );
        print 'At '
          . __LINE__
          . ' there are '
          . ( scalar keys %hash )
          . " keys: ";
        print Dumper(\%hash);

        my %hash2 = ( 1 => 5, 9 => 22 );
        print "This should delete one of the keys, using this hash ..\n";
        print Dumper ( \%hash2 );

        foreach my $key ( keys %hash2 ) { 

                if ( exists $hash{ $key } ) { 

                        $hash{ $key } -= $hash2{ $key };
                        if ( $hash{ $key } <= 0 ) { 

                                delete $hash{ $key };
                        }
                }
        }
        print 'At '
          . __LINE__
          . ' there are '
          . ( scalar keys %hash )
          . " keys: ";
        print Dumper(\%hash);
}

##</code><code>##

tab@music4:~/Pianoforte/Development/Perlmonks/11113721 $ perl hashkeys.pl
At 11 there are 4 keys: $VAR1 = {
          '9' => 44,
          '1' => 5,
          '3' => 12,
          '7' => 19
        };
This should delete one of the keys, using this hash ..
$VAR1 = {
          '1' => 5,
          '9' => 22
        };
At 33 there are 3 keys: $VAR1 = {
          '9' => 22,
          '3' => 12,
          '7' => 19
        };
tab@music4:~/Pianoforte/Development/Perlmonks/11113721 $