print "\"$topHash{$ryear}{$rmonth}{$rday}{$rhour}{$rminute}\"\n";

As you code stands now, you are literally passing the keys $ryear ("\$ryear"), $rmonth ("\$rmonth"), ... and you have not defined an entry for any of those keys. This is demonstrated in the following script:

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

my %hash = (1 => {1 => 1});
my $key = '1';

print "$hash{'$key'}{'$key'}\n";
print Dumper(\%hash);
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with output

Use of uninitialized value in concatenation (.) or string at junk.pl l
+ine 9.

$VAR1 = {
          '1' => {
                   '1' => 1
                 },
          '$key' => {}
        };
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Note how the inappropriate interpolation has resulted in the autovivification of the hash key '$key'.

That was it, thanks for the moment of clarity! I got tripped up because when explicitly stated the variables I had to single quote them.

Thanks for your help, I really appreciate it!
-Eric

No, you don't. When a key does not contain any white space or does not start with a sigil, Perl will automatically stringify it. Thus

print "$topHash{2010}{Feb}{11}{00}{03}\n";

is syntactically equivalent to

print "$topHash{'2010'}{'Feb'}{'11'}{'00'}{'03'}\n";.

See Scalar value constructors in perldata, for example.

If you put single quotes around the variables, you get literal strings as keys, such as '$ryear', not the value of the variable. Just leave the quotes off.

Sorry, spoke too soon... (Update: unstruck original note again, as on second thought it is in fact correct.)

elofland:

Just a couple minor notes:

1. Perl automatically creates hash table entries for you if you reference them, so you don't need to explicitly create them. (Search for "autovivification" for details.)
2. Perl treats an undef as a numeric 0 when you increment the value.

Example:

#!/usr/bin/perl -w
use warnings;
use strict;
my %topHash;

# (1) Perl automatically creates the hash table entries as needed
# (2) The undef value will be treated as zero, so the result of this
#     statement is that $topHash{77}{15}{Feb} is 1
++$topHash{77}{15}{Feb};

for my $k1 (keys %topHash) {
  for my $k2 (keys %{$topHash{$k1}}) {
    for my $k3 (keys %{$topHash{$k1}{$k2}}) {
      print "$k1 / $k2 / $k3 : '$topHash{$k1}{$k2}{$k3}\n";
    }
  }
}
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So you can simplify the first chunk of your code to:

...
while (<FILE>) {
   my $line=$_;
   (my $day,$month,$year,$hour,$minute) = ( $line =~ /^.*\[(\d*)\/(.*)
+\/(\d*):(\d*):(\d*).*$/);
   ++$topHash{$year}{$month}{$day}{$hour}{$minute};
}
close(FILE);
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...roboticus