You know that feeling, when the big program you've been working on approaches completion, and you're scanning for those invisible bugs the others will find when running your code. That's when I saw something like this somewhere between lines 6000 and 7000: 

my $one  = 1;
my $six  =
my $nine = 9;

print $six; # prints 9

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I didn't know you could chain lexical declarations like that! The bug survived for months because $nine was 0 and $six was supposed to be an empty string. Playing around with it reveals more questionable behavior: 

#!/usr/bin/perl -l

use strict;
use warnings;
use diagnostics;

print my $J = my $A = my $P = my $H =
'Just',' Another ','Perl',' Hacker';

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Does that look strict? :-)

In reply to If 6 Was 9 by Anonymous Monk

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