my @keys = grep { $hash{$_} eq 'value' }keys %hash; 

##</code><code>##

my %value;
push @{ $value{ $hash{$_} } }, $_ for keys %hash;
for ( keys %value ) {
    if ( @{ $value{$_} } > 1 ) {
        print "$_ :\n";
        print "\t$_\n" for @{ $value{$_} };
    }
}