Increment a hash value for each hash key (where the key is your date or filename in a HoH). Note that the use of Data::Dumper is just to show you the structure of the Hash of Hashes. It's up to you to figure out what to do with the data.

-fp

#!/usr/bin/perl

use Data::Dumper;
use strict;

my %count;

for my $i (3..6) {
     my $filename = "file.20020$i";
     open(DATA,$filename);
     while (<DATA>) {
          my ($name) = split(/\s+/,$_);
          $count{$filename}{$name}++;
     }
}

print Dumper %count;
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------------------------------------------------------------

Prints:

$VAR1 = 'file.200206';
$VAR2 = {
          'john' => '1',
          'chris' => '1',
          'lisa' => '1'
        };
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Update: Note about Data::Dumper, and removed parantheses from around split().