use feature ":5.14";
use warnings FATAL => qw(all);
use strict;
use Data::Dump qw(dump pp);

my @f1 = split /\n/, <<'END';
2010-nhw-es-ea-285, 2012-10-10
aab.external.audit.-.bvr.verif.externes, 2012-02-22
aashee.aziz, 2012-01-27
abbas.rangwala, 2012-01-27
abbie.gardner, 2012-09-10
ab.border-frontiere, 2012-08-11
abdool.yasseen, 2012-01-31
abdullah.aboukarr, 2012-08-10
abdullahi.sheikh, 2012-02-28
END

my @f2 = split /\n/, <<'END';
aaron.northway, CHIEF FINANCIAL OFFICER BRANCH 
aashee.aziz, HEALTH PRODUCTS AND FOOD BRANCH 
abbey.klugerman, HEALTHY ENVIRONMENTS AND CONSUMER SAFETY BRANCH 
abby.hoffman, STRATEGIC POLICY BRANCH 
abderrahim.boussanni, CHIEF FINANCIAL OFFICER BRANCH 
abdiaziz.nur, HEALTHY ENVIRONMENTS AND CONSUMER SAFETY BRANCH 
abdool.yassin, HEALTH PRODUCTS AND FOOD BRANCH 
abdoulie.manjang, N/A  
abdullah.hassen, HEALTH PRODUCTS AND FOOD BRANCH 
abdullah.patel, REGIONS AND PROGRAMS BRANCH
END

my (%f1, %f2); 

for(@f1)
 {my ($username, $date) = split /,\s*/;
  $f1{$username} = $date;
 }

for(@f2)
 {my ($fullname, $branch) = split /,\s*/;
  $f2{$fullname} = $branch;
 }

my %names = map {($_, 1)} (keys %f1, keys %f2);

say "$_, ", ($f1{$_}//'undefined'), ", ", ($f2{$_}//'undefined') for sort keys %names;