I don't know the subtle differences between the first two (I use them interchangably) but the third one: 
@a = undef;

[download]
is assigning a one element list to @a.... It's actually doing something like: 
@a = (undef);

[download]
Which is a relatively common error.

-Blake

In reply to Re: using undef on a array by blakem
in thread using undef on a array by Anarion

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