This may be old news for seasoned module authors, but I just got bitten by a new bug I wasn't really aware of before.

While debugging a script using Mail::Audit::Attach, I was wondering why the script would die at a certain point (it called a method on an undefined value). Finally, I found out the reason. The code was something like this: 

foreach (@attachments) {
    $_->method1;
    $_->method2;
}

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Unfortunately, method1 contained a loop using $_ and finally setting it to undef, thus causing the script to die on the next method call.

The funny thing is, I have used constructs like

{
    local $/ = undef;
    $data = <FILE>
}

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a lot of times, but somehow the concept never transferred itself to $_.

The solution, of course, is to either not use $_, or insert 

local $_

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in each method/function that uses it.

update (broquaint): title clarification (s/clutter/clobber/)

In reply to Is your module clobbering predefined variables? by crenz

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