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Re: Token Abuse Japh

by chargrill (Parson)
on Feb 10, 2006 at 21:15 UTC ( #529472=note: print w/ replies, xml ) Need Help??


in reply to Token Abuse Japh

I was also surprised that $ = was legal. Unfortunately,

perl -MO=Deparse

spoiled that fun, as well as teaching me to look out for that in the future :)

Being thoroughly impressed by this (as well as the rest of liverpole's JAPH's, I thougt I'd go ahead and post a detailed de-obfuscation of this particularly clever (to me, at least) JAPH.

First, the obfuscated code:

#!/usr/bin/perl + $ == _ eq _; $ -= ( ) = qw; ( );; $ *= $ -* $ -* $- ; $ /= $ -+ $ *; _: $ ".= chr $ /+ $ *** $ -; $ /= $ / >> $ = || $ ** $ -; $ /= $ / &~ $ */ $ - and goto _; + print $ "," "

Pretty confusing! But let's run it through -MO=Deparse, and we get:

$= = '_' eq '_'; $- = () = ('(', ')'); $* = $- * $- * $-; $/ = $- + $*; _: $" .= chr $/ + $* ** $-; $/ = $/ >> $= || $* * $-; $/ = $/ & ~$* / $- and goto _; print $", "\n";

Still pretty confusing, but at least now I can parse it a little better.

$= = '_' eq '_';

$= normally defaults to 60 as the current page length of the selected output channel, but this just sets it to 1.

$- = () = ('(',')');

$- = () = qw; ( );; is like $- = () = ('(',')');

('(',')') is a two element list, and the =()= idiom Perl Idioms Explained - my $count = () = /.../g shows that $- receives the count of elements in the list, in other words 2.

$* = $- * $- * $-;

Equivalent to $* = 2 * 2 * 2, or 8.

$/ = $- + $*;

Sets $/ to 10.

_: $" .= chr $/ + $* ** $-;

_: is a line label, and I thought (as Errto noted above) it had to be at the begining of a line. $=, the list separator for list values interpolated into a double quoted string, defaults to a single space. The statement is equivalent to $" =  " " . chr 10 + 8 ** 2 , and ** binds tighter than + , therefore $" = " " . chr 10 + 64, or rather
$" = " J".

$/ = $/ >> $= || $* * $-;

This is: $/ = 10 >> 1 || $* * $-;

10 >> 1 will evaluate true (non-zero), so the right half doesn't gets evaluated, and $/ is subsequently set to 5.

$/ = $/ & ~$* / $- and goto _;

This can be written as $/ = 5 & ~ 8 / 2 , or a bit more clearly, $/ = 5 & ( ( ~ 8 ) / 2 ). This has the net effect of setting $/ to 1.

Going to the "_" line label, $= (currently " J") has chr 1 + 64, or "A" appended to it. then 1 >> 1 evaluates to 0, so this time the right hand of the expression is evaluated, and $/ is set to 8 * 2, or 16. Then $/ = $/ & ~ $* / $- can be restated as $/ = 16 & ( ( ~ 8 ) / 2 ), and sets $/ to 16.

Back to the "_" line label. $= (currently " JA") has chr 16 + 64, or "P" appended to it. 16 >> 1 is 8, so $/ is set to 8. and 8 & ( ( ~ 8 ) / 2 ) evaulates to 8.

Back to the "_" line label, $= (currently " JAP") has chr 8 + 64, or "H" appended to it. Then 8 >> 1 is 4, so $/ is set to 4. And what I think is the really clever "bit" ;) is that now 4 & ( ( ~ 8 ) / 2 ) evaluates to 0, so and goto  _; is skipped, proceeding to:

print $", "\n";

... which I think is pretty self-explanatory.

Whew! ++liverpole! That was a lot of fun!



--chargrill
$/ = q#(\w)# ; sub sig { print scalar reverse join ' ', @_ } + sig map { s$\$/\$/$\$2\$1$g && $_ } split( ' ', ",erckha rlPe erthnoa stJu +" );


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Re^2: Token Abuse Japh
by liverpole (Monsignor) on Feb 10, 2006 at 22:52 UTC
    Thank you, chargrill ++ a delightful read.

    I'm glad you referenced Perl Idioms Explained - my $count = () = /.../g, because I actually hadn't intended to use it; I just came to a point where I realized I needed it.  So it was serendipitous that I had just read that node the other day.


    @ARGV=split//,"/:L"; map{print substr crypt($_,ord pop),2,3}qw"PerlyouC READPIPE provides"

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