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    <h3>Here is how you figure out how to de-obfuscate this subroutine.</h3> <p><em>Sorry for the length</em></p> <p>First let's tidy up the code, and add useful comments.</p> <pre><code>sub foo { [ ( # ($#{$_[1]}) $#{ $_[ ! ( $| | $| ) # $OUTPUT_AUTOFLUSH === $| # $| is usually 0 # ! ( $| | $| ) # ! ( 0 | 0 ) # ! ( 0 ) # 1 ] } * # @{$_[1]} @{ $_[ !!$_ ^ !$_ # !! 1 ^ ! 1 # ! 0 ^ 0 # 1 ^ 0 # 1 # !! 0 ^ ! 0 # ! 1 ^ 1 # 0 ^ 1 # 1 ] } ) ? # @{$_[1]} @{ $_[ !$. . !!$. # $INPUT_LINE_NUMBER === $. # $. starts at 1 # !$. . !!$. # ! 1 . !! 1 # 0 . ! 0 # 0 . 1 # 01 ] } [ # $_[0] $_[ # @LAST_MATCH_START - @LAST_MATCH_END # 0 @- - @+ ] % # @{$_[1]} @{ $_[ $= =~ /(?=)/ / !$` #( fix highlighting )`/ # $= is usually 60 # /(?=)/ will match, returns 1 # $` will be '' # 1 / ! '' # 1 / ! 0 # 1 / 1 # 1 ] } .. # $#{$_[1]} $#{ $_[ $? ? !!$? : !$? # $CHILD_ERROR === $? # $? ? !!$? : !$? # 0 ? !! 0 : ! 0 # 0 ? 0 : 1 # 1 # 1 ? !! 1 : ! 1 # 1 ? 1 : 0 # 1 ] } , # ( 0 ) ( $) ? !$) : !!$) # $EFFECTIVE_GROUP_ID === $) # $) ? !$) : !!$) # 0 ? ! 0 : !! 0 # 0 ? 1 : 0 # 0 # 1 ? ! 1 : !! 1 # 1 ? 0 : 1 # 0 ) .. # $_[0] $_[ $- - $- # 0 # $LAST_PAREN_MATCH = $- # 1 - 1 == 0 # 5 - 5 == 0 ] % # @{$_[1]} @{ $_[ $] / $] # $] === The version + patchlevel / 1000 of the Perl interpreter. # 1 / 1 == 1 # 5 / 5 == 1 ] } - # ( 1 ) ( !!$+ + !$+ # !! 1 + ! 1 # ! 0 + 0 # 1 + 0 # 1 ) ] : # @{$_[1]} @{ $_[ !!$^^ ^ !$^^ # !! 1 ^ ! 1 # ! 0 ^ 0 # 1 ^ 0 # 1 # !! 0 ^ ! 0 # ! 1 ^ 1 # 0 ^ 1 # 1 ] } ] } </code></pre> <p>Now let's remove some of the obfuscation.</p> <pre><code>sub foo{ [ ( $#{$_[1]} * @{$_[1]} ) ? @{$_[1]}[ ( $_[0] % @{$_[1]} ) .. $#{$_[1]} , 0 .. ( $_[0] % @{$_[1]} - 1 ) ] : @{$_[1]} ] } </code></pre> <p>Now that we have some idea of what is going on, let's name the variables.</p> <pre><code>sub foo{ my( $item_0, $arr_1 ) = @_; my $len_1 = @$arr_1; [ # This essentially just checks that the length of $arr_1 is greater than 1 ( ( $len_1 -1 ) * $len_1 ) # ( ( $len_1 -1 ) * $len_1 ) # ( ( 5 -1 ) * 5 ) # 4 * 5 # 20 # 20 ? 1 : 0 == 1 # ( ( $len_1 -1 ) * $len_1 ) # ( ( 2 -1 ) * 2 ) # 1 * 2 # 2 # 2 ? 1 : 0 == 1 # ( ( $len_1 -1 ) * $len_1 ) # ( ( 1 -1 ) * 1 ) # 0 * 1 # 0 # 0 ? 1 : 0 == 0 # ( ( $len_1 -1 ) * $len_1 ) # ( ( 0 -1 ) * 0 ) # -1 * 0 # 0 # 0 ? 1 : 0 == 0 ? @{$arr_1}[ ( $item_0 % $len_1 ) .. ( $len_1 -1 ), 0 .. ( $item_0 % $len_1 - 1 ) ] : # If we get here, @$arr_1 is either empty or has only one element @$arr_1 ] } </code></pre> <p>Let's refactor the code to make it a little bit more readable.</p> <pre><code>sub foo{ my( $item_0, $arr_1 ) = @_; my $len_1 = @$arr_1; if( $len_1 &gt; 1 ){ return [ @{$arr_1}[ ( $item_0 % $len_1 ) .. ( $len_1 -1 ), 0 .. ( $item_0 % $len_1 - 1 ) ] ]; }elsif( $len_1 ){ return [ @$arr_1 ]; }else{ return []; } } </code></pre>
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    1. POObfuscation Puzzle: Can you figure out what this Perl function does?
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    1. COThe if( $len_1 ) part is wrong; the raw code is checking two different conditions.
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    2. COErr, and so the else clause isn't correct. And the $arr_1->[] syntax is not equivalent to the @{}[].
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    3. COFixed the afore mentioned errors.
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