or download this
$length_of_u = length($u); # how long is this string?
$how_many_characters_short = 6-$length_of_u; # how far are we from ha
+ving 6 characters?
...
$padding = '0' x $how_many_characters_short; # this will give us as ma
+ny 0's as $how_many_characters_short is long (e.g. if it is 4 - it gi
+ves us '0000')
$u = $padding.$u; # concatenate them together... finished!