#!/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);
}