Perl: Reference

1. Hash reference

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

my $hash_ref = {}; # make a hash reference;

while (<DATA>) {
    chomp;
    my ($key, $value) = split;
    $hash_ref->{$key} += $value; # dereference: $hash_ref->{$key} = ${$hash_ref}{$key};
}

for my $key (sort {$a cmp $b} keys %$hash_ref) { # %$hash_ref = %{$hash_ref};
    print "$key\t$hash_ref->{$key}\n";
}


__DATA__
bb  1
bb  8
aa  2
aa  4
cc  6 

Output:

aa  6
bb  9
cc  6