Obfuscated Perl

Originally published on: Tue, 07 Jul 2009 11:33:26 +0000

In 1997, I entered a contest held by the publication The Perl Journal. It was their 1st annual Obfuscated Perl coding contest.

My entry in the category for simply printing "The Perl Journal" took 2nd place. ( You can now find this entry in the O'Reilly book Games, Diversions, and Perl Culture ).

I would like to briefly explain the genesis of my entry.

I had thought about listing my entry here, but I'm pretty certain that I don't own any kind of publication rights. One can still find it with a little Googling. However, the first two phases of the entry are still mine.

The program began with an idea that I had that involved allowing the Perl program read data from its own set of comments. The code opens itself as a file, loads its own source ( including the comments ).

To confuse the reader, I small p-machine and interpreted a short program to read from the comments and display The Perl Journal.

# Jim Lawless jimbo@radiks.net
# This program is an entry for the
# obfuscated Perl contest.

open(i,$0);@x=<i>;$y=join("",@x);close(i);
@z=split(/\ /,$y);
$c{"]"}='$d++;';
$c{">"}='$e++;';
$c{"?"}='print substr($z[$d],$e,1);';
$c{"["}='$d--;';
$c{"<"}='$e--;';
$c{"."}='print " ";';

$d=0; $e=0;

$f="]]]]]]?>?[[[[>>>?]]].]]]]]]]]]<<<<?>?>?>?[[[[[[[[.[[[[[<<<?" .
"]]](fix this)]>>>>?]]]]]]]]<?[[[?]]]]]<?[[[[[[[[[[[[[<?>>?";

for($i=0;$i<length($f);$i++) {
eval($c{substr($f,$i,1)});
}

The associative array %c holds the code for the six instruction machine.

The symbolic instructions are as follows:

] Increment variable $d
> Increment variable $e
? Display the character in array $z, element $d, at position $e
[ Decrement variable $d
< Decrement variable $e
. Print a space

The p-machine program that performed the output was embedded in the Perl code as the string:

$f="]]]]]]?>?[[[[>>>?]]].]]]]]]]]]<<<<?>?>?>?[[[[[[[[.[[[[[<<<?" .
"]]](fix this)]>>>>?]]]]]]]]<?[[[?]]]]]<?[[[[[[[[[[[[[<?>>?";

Once I had the p-machine interpreter, I needed to make the code more unreadable. I took half of the top portion of the code and half of the lower portion and then interlaced the characters of each. I added a for loop to the final code that separated the two halves, concatenated them, then called eval() to interpret the original program.

   for($i=0;$i<368;$i+=2){$s=substr($v,$i,1);$q=$q .
   (($s eq '|') ? "'" : $s);$s=substr($v,$i+1,1);$r=$r .
   (($s eq '|') ? "'" : $s);}eval( $q . $r);print "\n";

Unless otherwise noted, all code and text entries are Copyright Š2009 by James K. Lawless

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