Shorter code does not necessarily mean faster code. If you need to compose a username from first, last names and date of birth, you can have:

use strict;

my $bday = "8/16/97";
my $firstname = "Benjamin";
my $lastname = "Biederman";

my $uname = lc(substr($firstname,0,1) .
  substr($lastname,0,1)) .
  sprintf("%02d"x3, split m|/|, $bday);

print $uname;
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Is that what you want ?