Do you know about the ref function? You can use it to tell what kind of data is referenced, affecting how you handle it.

Here's a very quick-and-dirty subroutine show_this() that uses ref to recursively inspect the contents of your hash. As such, it's a primitive replacement for Data::Dumper:

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

my %singleLevelHash = ();

my %multiLevelHash = (
    'firstSampleKey' => 'SampleValue',
    'secondSampleKey' => {
    'secondLevelSampleKey' => { 
        'thirdLevelSampleKeyOne'   => 'thirdLevelSampleValue',
        'thirdLevelSampleKeyTwo'   => 'thirdLevelSampleValue',
        'thirdLevelSampleKeyThree' => 'thirdLevelSampleValue',
    }
    }
);

# print Dumper \%multiLevelHash;
show_this(\%multiLevelHash);

# foreach my $firstSampleKey ( sort keys %multiLevelHash ) {
#     print $firstSampleKey . "\n";
#     foreach my $secondLevelSampleKey ( sort keys $multiLevelHash{$fi
+rstSampleKey} ) {
#     print $secondLevelSampleKey . "\n";
#     }
# }


sub show_this {
    my ($x) = @_;

    if (ref $x eq "") {
        printf "  Value: '%s'\n", $x;
    } elsif (ref $x eq 'SCALAR') {
        printf "  SCALAR ref:  '%s'\n", $$x;
    } elsif (ref $x eq 'HASH') {
        print "  HASH ref '$x':\n";
        foreach my $key (keys %$x) {
            my $val = $x->{$key};
            print "  $key:  ";
            show_this($val);
        }
    } elsif (ref $x eq 'ARRAY') {
        print "  ARRAY re '$x':\n";
        foreach my $val (@$x) {
            show_this($val);
        }
    }
}
[download]

Hopefully that gives you an idea how to interpret a HASH ref, differently from a scalar value. Hint -- the solution is in the block:

    foreach my $key (keys %$x) {
        ...
    }
[download]