comment on

This is a meditation about solving a problem which was inadvertently introduced into a working Perl program, and and an invitation to the reader to discover for himself/herself the cause of the problem.

A couple of days ago I was toying with the idea of creating a new obfuscation/Japh, and towards that goal created a very simple program to display random characters from a given set so that I could see which symbols looked good together.

My first stab at the program was working okay, and was basically something like this:

#!/usr/bin/perl -w

use strict;
use warnings;

#
#  Try chars from space ' ' (ascii 32) up until
#  tilde '~' (ascii 126).
#
foreach (32 .. 126) {
    my $c = chr($_);
    try_char($c);
}

sub try_char {
    my ($new_char) = @_;
    print "=== Character '$new_char' ===\n";
    my @chars = qw( . o O );
    if ($new_char) {
        push @chars, $new_char;
    }
    for (my $i = 0; $i < 800; $i++) {
        my $r = $chars[int(rand @chars)];
        print $r;
    }
    print "\n";
    <STDIN>;      # Wait for user to hit [RETURN]
}
[download]

The program would display a screenful of random characters each time the subroutine try_char was called, from the basic set {'.', 'o', 'O'}, with a single additional character temporarily added to the basic set on each call to the subroutine. At the end of the subroutine, the user (me) could view the random mix of characters, and then type <RETURN> to continue to the next subroutine invocation.

This worked fine, and produced the following sample outputs:

=== Character ' ' ===
OoOO oOo.ooOoO ooO o  . oOOOOOO.OO oo . O o.o.Oo...O..OoOOooOO oooo..O
+OOo......O
 O.o  o .O.o o .O O. OO. . o OooO ..oO.ooOOOo Oo  . o.ooooOoo   .O oO.
+oO..Oo.ooO
O.o Oo. O  O.ooO.oo   Oo. oO. Ooo..o..O Oo.OO.O.O..Oo oOOo.OO..oOoOOo.
+OooOoOOOo.
 OO..O. oOOOoooOOoO.OO.  OO. O.o.. O.O..oO.O.oo oo.OoO OOoo.oOOoOo.Oo.
+ OOOOoo O
    OO O oO.oO o .Oo..oo.  .Oo.Ooooooooo  Oo o. O.o  .Oo.oO... o.. O  
+Oo o.o.O .
. oo oo .O.o .O ..oO.OOo.OO O OO  .OooOooooOo . O. .OO...OoooOOO. .O.o
+oOo OoO. o
o OoO.  OoOo.OO  O o. oO .o  ..  o.oOOO   Oo.OOo . o.oO. .oo ..oOoo oO
+..OO O.O .
Ooo OO.O.Ooo o  o O. ..OooO O oo Oo.O.oo.o  OO.o oo OO   ooo .. .Oo O 
+  o.ooO. .
oOOO. .oo.o. oo O O ..o Oo.O...O   o.O.ooo  O oOoo OoO .oo.OO.O.O.OO  
+ .. ... oo
OOo o .Oo. ooO Ooooo.O  O.oOoOooo OOoo. O...oO OOOoO.O.O o. .Ooo.OoOo.
+ .O OO O.o

=== Character '!' ===
!.!oo!oO!!Oo!!.o..OO.oOoO.O.ooo!.!OO!!oooOoO!!.OO..!OO!!!O!.!!O!!.!O.O
+!.oO..o.oO
OO.o.O..o.!oOO..O.oOoo!!!..!O....!o!!!!.oo!o.O.o!.OO!.OooO.!.OO.OO!OOo
+.!OO!O!...
.O!O.ooOOo!!!o!o!.ooo.o!..!o!O.oO.oOo!O.!.O.Oo.!O!!!!oo!.!.oo..o.oOo!!
+.OO..O!ooo
oo.!.!!OOO!.Oo!O.o.O!.!o.O!Oo!O.oO.!oOo!!OOO..!!OO!O.!OOOOO!!...o!oOo!
+OooOOO!!oO
.ooO.oOO.oo!oo.o.O.!.!..o.oO!!..O..oo.oo!!oo!.!!.O!Oo!!ooo.!!!o.!o.oOo
+!OO.O.ooo!
OOOO!o.O!!Oo!O.Oo!!!Oo.!..O!!o.o.O!!O.!OOooo!!!.Oooo..!o.O.oO..!oOO.O!
+o.!ooo.O!!
..o.o!O.OoOo.!Oo..!.O.oo!o!O!O.!!!O!!O.oOOo!ooO.!!!.!oo.o.!oo.o.!!.O!o
+oo!O!o!OO.
!o!.!!.O..!.O.oooo.O!.oOO.!..!o.OOo.oOOO.o..!!O.!!OOOoo.o..!!oo..o!.Oo
+oOOoO!!!..
.OOO.!oO!!!!ooO!..o.!!.oo..!OOo!.o..OO!.O!.O!o.o!OOOOo!o!O!!oOo.O.O.!o
+oo.!.Oo..O
.o.oOOOOo.o!o.oo.ooOooOO!!OO.o!.!O!O..O.!.O!!oOOoo!!.Ooo.O.OoO!o!.oO.o
+OOo.Oooo!o


=== Character '"' ===
""o.o.o..oo.O.O."o"OoOO"""o..O"OOo.OOOoO".."".oO.."..o.""O.oOoo.o.""o"
+.o.o.o".""
O.o.."..O.o.".O".oo."OOOoo"Oo..".O...o."oo"."oOo"O.o."OO."o"O.o"O".oO"
+oOO.."""""
""OoO""O.."O.Oo."oOooooO"o.OoO".""OO"OOO".."oOo"o".OoO""Oo.OOoooO."..o
+O"..."ooo"
o.ooO.O""o"o.."o""O".".Oo..oO.o.".oo""Oo"o..oOOooo""o.Oo"."O"".oO"".O.
+."OOO...".
Oo.."."oO....o"ooo."Oo."o.o.o""."Oo.O"."oo".o.o.""oO.oooO"Oo..O""OO.oO
+O.O.o.oo"o
o".O"oOoOooO"oooooO.OO.."..""o"oOo."O"o.o.""ooOo.ooO.ooOo.oOo"Oo.o""..
+o".OoOoo..
O."oO""OOO"oOO"oOOoo.oo""o.O""o"..o.O""o".o.Oo"oOO".""OooO""Oo."oO."O"
+oO""".OOO.
oOO"".o"OOo"oO.Ooo.""oOO"o."o"oOOoOooO.o..Oo.o"oOO"oOOoo".."O."Oo."O."
+"O"O"..O"o
"o."o".oO"O.OooO.."oo"."""...o..o."O".O.O"o...""..OO"o"o.""Oo"O."o"Ooo
+Oo".o""...
oO...o""OOO.".O.oOOoo"oo".o."o"."oo.o"""OO."o.o.O.o.."o."o.""..O"o"o"O
+oO."."OOo"
[download]

At this point I decided to skip all of the alphanumerics ('a' ... 'z', 'A' ... 'Z', '0' ... '9'), and thought it would be easier to manage it in a map, so as a first step, I rewrote the foreach loop thusly:

#foreach (32 .. 126) {
#    my $c = chr($_);
#    try_char($c);
#}
map {
    my $c = chr($_);
    try_char($c);
} (32 .. 126);
[download]

I was surprised to see that typing <RETURN> no longer let me advance to the next iteration! Instead, the program would echo the newline, and yield no new output at all.

At this point, you may want to try the program for yourself to see if you can discover what's happening. If you'd prefer not to (or if you get stuck), here is what I learned:

s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/

In reply to Taken out of Context by liverpole

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		`&`
	<		`<`
	>		`>`
	[		`[`
	]		`]`

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.