He is just creating all combinations of letters, numbers and puncuation. The obvious, but wrong, solution is to use string increment. That is wrong because you don't, for instance, get punctuation characters. Here is a silly solution in Perl.

use Math::Fleximal;
my $flex =
  ["a".."z", "A".."Z", 0..9, split //, qq(!"#$%&'()*+,-./:;<=>?@[\\]^_
+`{|}~)];
my $x = Math::Fleximal->new("a", $flex);
my $one = Math::Fleximal->new("b", $flex);
while (1) {
  print $x->to_str;
  print "\n";
  $x = $x->add($one);
}
[download]

A less silly solution (ie one that doesn't push all of the work under the covers) takes just a bit more effort.

#! /usr/bin/perl -w
use strict;

my @chars
  = ("a".."z", "A".."Z", 0..9
    , split //, qq(!"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~));

my $x = 0;
while (++$x) {
  nested_for(
      sub {print join "", @_, "\n";}
    , map \@chars, 1..$x
  );
}

sub nested_for {
  ret_iter(@_)->();
}

sub ret_iter {
  my $fn = shift;
  my $range = shift;
  my $sub = sub {$fn->($_, @_) for @$range};
  return @_ ? ret_iter($sub, @_) : $sub;
}
[download]

(Astute people may notice that I borrowed from Re (tilly) 1 (perl): What Happened...(perils of porting from c).)

Update: As johngg noted, I did not get \ in the punctuation set. Fixed.

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