• Whenever you have to do a numeric calculation, make sure you multiply by the return value from your last print.
• Speaking of print, there's no need to ever pass any arguments to it.

  {
    local $_="Hello ";
    local $\="world\n";
    print;
  }
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• !$, looks pretty non-obvious, but unless you've been tinkering with the $, variable, it's equal to 1. 1 is a number that comes up quite frequently, so be sure to use !$, liberally. Another synonym for 1 is !!$$.
• On that note, why say unless $foo when you can say if!!$$==!$foo.
• In general, most of the variables in perlvar are pretty obscure.

I'll add some more later...

#!/usr/bin/perl
use strict;use warnings;
    my $num =3;
    $"=',';print join "\n",glob join "_",("{@{ [1..12] }}")x$num;
___END___
1_1_1
1_1_2
1_1_3
1_1_4
1_1_5
1_1_6
...
12_12_7
12_12_8
12_12_9
12_12_10
12_12_11
12_12_12
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#!/usr/bin/perl
use strict;no strict 'refs';use warnings;use re 'eval';

    my $num =3;
    $"='.*?';"@{ [1..12] }" =~ /@{[ ('\b(\d+)\b')x $num]}(?{{print ((j
+oin "_",map {$$_}1..$num),"\n")}})(?!)/;
__END__
1_2_3
1_2_4
1_2_5
1_2_6
1_2_7
...
8_11_12
9_10_11
9_10_12
9_11_12
10_11_12
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"1 2 3 4" =~ /\b(\d+)\b.*?\b(\d+)\b(?{{print "$1_$2\n"}})(?!)/;
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As argued in The Lighter Side of Perl Culture (Part III): Obfu constraints are the heart of obfu. Some examples from that node:

• Constrain yourself to a restricted character set. For example, from A++, ${~$/&~$;&$^}++ uses only punctuation chars, while y ccccd x s vvchr oct oct ord uc ave x s vvucve le s vvuc ave x s vvchr oct oct oct ord uc bve x eval uses only alphabetic chars.
• Constrain the code to the theme of the obfu shape. For example, when tuning Saturn, I changed O^N^E}(@X,1.6) to S|A|T|U}(@R,$N) to better align the code to the Saturnian theme.
• Find an arbitrary constraint. For example, another A++ from mtve is constrained to being a palindrome: !$A+++!q!+++A$!

mm these are all interesting.. a liip using something like regex would be nice.. printing "hello world\n" 10 times for example..

still looking for magic! :D

I had no idea you could replace regex delimiters with... whatever! Can't wait to make my one-liners even more annoyingly obfuscated =P

Beware that some delimiters have special meanings. e.g. m/$foo/i interpolates $foo whereas m'$foo'i does not.

Regular expressions are not the only delimiters that can be replaced with whatever. qq(), q(), qx() and qw() work similarly. For example, the following assigns a string consisting of a single space character to $foo:

my $foo = q q q;
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perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'