in reply to uninitialized $_ sneaks past warnings in grep/map block or expression

Are you sure it's not documented in perlvar? The entry for $_ states when it is used as an iterator or the destination of an input record for a while loop. If it's not defined, it's not defined. If it is being given a value by a for loop, a while loop with a readline operator, given, grep, or map, then it is defined.
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Re^2: uninitialized $_ sneaks past warnings in grep/map block or expression
by JavaFan (Canon) on Sep 01, 2010 at 16:00 UTC
    If it is being given a value by a for loop, a while loop with a readline operator, given, grep, or map, then it is defined.
    Not if the value given isn't defined. 
    $ perl -wE 'say for 1, undef, 3'
1
Use of uninitialized value in say at -e line 1.

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      That's a trick. You've very specifically given it a non-value. ;-)

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