if you just want the 3 letter combinations of the 26 lowercase letters in the English alphabet, this is pretty simple and probably very fast:

#!/usr/bin/perl -w
use strict;
my $size = 3; # number of characters in the target string.
my $string = 'a' x $size;
my $end = 'z' x $size;
do {
  print $string++, "\n";
} while $string ne $end;
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This would also work for uppercase, but as soon as you want to mix cases, add numbers, and add punctuation it falls short as a solution.

The mechanism used here is the automagical increment operator (++) which does cool stuff when applied to a string starting with a letter and consisting of letters and numbers.

Update: If you want to start with 1 character strings and go up to N characters, just change the initialization to:

my $string = 'a';
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