G'day jzelkowsz,

Here's a solution using Text::CSV (if you have Text::CSV_XS installed it will run faster) and in-memory files (see open). The input data I used is a verbatim copy of what you posted here.

#!/usr/bin/env perl

use strict;
use warnings;

use Text::CSV;

my ($hr_file, $ad_file, $com_file) = qw{hr.txt ad.txt com.txt};

my (@col_index, %hr_record_for);

my $csv = Text::CSV::->new({quote_space => 0})
    or die "Can't instantiate a Text::CSV object: ",
            Text::CSV::->error_diag();

{
    open my $mem_fh, '<', canonicalise_file_in_memory($hr_file)
        or die "Can't read in-memory file: $!";

    @col_index = @{$csv->getline($mem_fh)};

    while (my $row = $csv->getline($mem_fh)) {
        $hr_record_for{$row->[0]} = $row;
    }
}

{
    open my $mem_fh, '<', canonicalise_file_in_memory($ad_file)
        or die "Can't read in-memory file: $!";
    open my $out_fh, '>', $com_file
        or die "Can't write '$com_file': $!";
    
    (undef) = $csv->getline($mem_fh);

    while (my $row = $csv->getline($mem_fh)) {
        for my $i (1 .. $#col_index) {
            if ($hr_record_for{$row->[0]}[$i] ne $row->[$i]) {
                $csv->say($out_fh, [
                    $row->[0], $col_index[$i],
                    $hr_record_for{$row->[0]}[$i]
                ]);
            }
        }
    }
}

sub canonicalise_file_in_memory {
    my ($file) = @_;

    open my $fh, '<', $file or die "Can't read '$file': $!";

    my $canon;

    while (<$fh>) {
        chomp if /,$/;
        $canon .= $_;
    }

    return \$canon;
}
[download]

Output:

$ cat com.txt
barsu991,mail,Uttiam.Barski@pulse.org
barsu991,title,Director of Cooks
walkl003,givenname,Lreblemet
walkl003,employeenumber,20178941
walkl003,mail,Lreblemet.Walker@pulse.org
walkl003,title,Head Cook
karss001,givenname,Sovyetk
karss001,mail,Sovyetk.Karsten@pulse.org
karss001,title,Dishwasher
karss001,physicaldeliveryoffice,Kitchen of the World
karss001,streetaddress,205 Willy B. Temple
karss001,st,WI
karss001,postalcode,50987
zingk072,givenname,Kovon
zingk072,employeenumber,20113578
zingk072,symphonyemployeetype,IKP
zingk072,mail,Kovon.Zingerman@pulse.org
zingk072,manager,"cn=manager1,ou=users,ou=Kitchen,dc=Kitchen,dc=net"
hutcy231,givenname,Yello
hutcy231,mail,Yello Hutchinson
haserz221,sn,Haserkrilk
haserz221,employeenumber,20125471
haserz221,mail,Zebediah.Haserkrilk@kit.org
haserz221,telephonenumber,
[download]