#!/usr/bin/perl
#
use strict;
use warnings;
use Data::Dumper;

my %hash1;
my %hash2;
foreach my $line (<DATA>) {
    my ($key, $value) = split(/\s+/, $line);
    push(@{$hash1{$key}}, $value);
    push(@{$hash2{$value}}, $key);
}

print Dumper(\%hash1);
print Dumper(\%hash2);

print "Values for key a are @{$hash1{a}}\n";
print "Keys with value b are @{$hash2{b}}\n";
print "Keys with value h are @{$hash2{h}}\n";

__DATA__
key value
a   b
a   c
a   d
e   f
g   h
g   i
j   h