the hazards of coding for webservers vs. shell scripts

[kareila]

When I was doing some code cleanup a few months ago, I saw some lines that looked like this:

my $foo;
$foo = $bar unless $baz;

I decided that looked redundant and changed it to:

my $foo = $bar unless $baz;

Take my advice: don't combine "my" statements and postfix conditionals. Ever.

I've updated the programming guidelines to warn people away from this as well.

The manifestation of this particular bug was to cause the $foo variable to be referenced in global scope if the conditional was false. In that situation, the assigned value would persist across execution threads, such that if two people in a row had a true $baz, the second user would see the first user's value of $foo. Even with use warnings and use strict in effect, Perl apparently thinks this is perfectly fine.

ETA: exor674 says this command will find it (but not in BML files):

perlcritic --single-policy ProhibitConditionalDeclarations

Comments

[janinedog]

Interesting. I know that I never wrote stuff like "my $foo = $bar unless $baz", but that was simply because it's not clear what $foo is in the case that it's not $bar (undef? or does it just not exist at all? or something else?). And I like my code to be clear, which is why I generally use a ternary if I want to do a simple assignment on one line.

I never realized it actually causes problems like this, though!

[kareila]

An unassigned variable has a value of undef.