If the padding is only for printing (i.e., output), one can also do:

c:\@Work\Perl\monks>perl -wMstrict -le
"use constant MIN => 5;
 ;;
 my $s = '';
 for my $c ('', 'a' .. 'h') {
   $s .= $c;
   printf qq{%12s -> '%-*s' \n}, qq{'$s'}, MIN, $s;
   }
"
          '' -> '     '
         'a' -> 'a    '
        'ab' -> 'ab   '
       'abc' -> 'abc  '
      'abcd' -> 'abcd '
     'abcde' -> 'abcde'
    'abcdef' -> 'abcdef'
   'abcdefg' -> 'abcdefg'
  'abcdefgh' -> 'abcdefgh'
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See sprintf for discussion of the  * format specifier.