my $agency = 'XY';      # A string between 1 and 3 characters long
my $date = '2007/6/3';  # Or whatever date format
my $type = 'T';         # A single character

##</code><code>##

my $string = join '', sprintf( '%-3s', $agency ),
                      sprintf( '%04d%02d%02d', split /\//, $date ),
                      $type;