String rewriting is all in The Science of Fractal Images, ed Peitgen & Saupe (Springer-Verlag, 1991, ISBN: 0387966080). Of course, they were using an awkward Pascal-like pseudocode language with no regular expressions ...

Here's at least part of the famous snowflake. I think I changed three lines:

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

my $depth   = 4;
my $start   = '_/_\_/_';    # _ = forward, / = left, \ = right
my $fractal = $start;

$fractal =~ s/_/$start/og for ( 0 .. $depth );

$fractal =~ s/_/0 0.8 rlineto /g;
$fractal =~ s,/,60 rotate ,g;
$fractal =~ s,\\,240 rotate ,g;
print '%!', "\n", '0.1 setlinewidth 500 100 moveto ', $fractal,
  'stroke showpage', "\n";
[download]

Now what would be really cool would be a Perl routine that would parse ASCII-art axioms and production rules, and generate the fractal. My free time is not that copious.

--
bowling trophy thieves, die!

Fractals generated by iterative text replacement rules on strings interpreted as drawing instructions are called L-systems, if memory serves.

Makeshifts last the longest.

Neat short code for Koch curve. Good demonstration of the synergy between Perl and PostScript to produce graph real fast, esoteric code and large uncompressed PS file size notwithstanding.