Seems that nobody has pointed this out yet - there is a convenient way to access data stored in your flat file. By using DBI and DBD::CSV modules.

use strict;
use DBI;
use DBD::CSV;
use Data::Dumper;

# Connect to CSV database
my $dbh = DBI->connect("DBI:CSV:csv_sep_char=\|")
                or die "Cannot connect: " . $DBI::errstr;
$dbh->{'csv_tables'}->{'addressbook'} = {'file'=>'addressbook.txt' };

# load address book entries
my $sth = $dbh->prepare("SELECT * FROM addressbook");
$sth->execute();

# store data in 2-tier hash table
my %data;
while (my $res = $sth->fetchrow_hashref()) # loop through data
{
   # create hash to store details
   my %rec = map { $_ => $res->{$_} } @{$sth->{NAME}};

   # create top level hash with last name as lookup key
   $data{$rec{"last"}} = \%rec;
}

# cleaning up
$sth->finish;
$dbh->disconnect;

# inspect our result
print Dumper(\%data);
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The data file -

addressbook.txt
---------------
title|first|last|room|phone|email
Mrs|Linda|Caralo|201|148|she@borg.org
Miss|Jean|Androno|317|167|j@alo.com
Mr|Steve|Paterman|101|100|steve@net.net
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And the hash structure built with the above script:

$VAR1 = {
          'Caralo' => {
                        'email' => 'she@borg.org',
                        'first' => 'Linda',
                        'last' => 'Caralo',
                        'title' => 'Mrs',
                        'phone' => '148',
                        'room' => '201'
                      },
          'Paterman' => {
                          'email' => 'steve@net.net',
                          'first' => 'Steve',
                          'last' => 'Paterman',
                          'title' => 'Mr',
                          'phone' => '100',
                          'room' => '101'
                        },
          'Androno' => {
                         'email' => 'j@alo.com',
                         'first' => 'Jean',
                         'last' => 'Androno',
                         'title' => 'Miss',
                         'phone' => '167',
                         'room' => '317'
                       }
        };
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