in reply to Lexical scope variable is not undef'ed

(Update: I am misled -- ignore the following)

Your problem is this statement: 

my $var = '' if 0;

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Which is being parsed as: 
if (0) { my $var = ''; }

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...And in turn, the statement is skipped entirely. Therefore you are never creating a lexical variable $var -- you are implicitly using a local variable $var, which retains its value from iteration to iteration and then resets itself once the loop is exited.

perlsyn explains it.

Example: 

bash$ perl -e 'for(1..3){my $i if 0; print $i++, "\n"}'
0
1
2

bash$ perl -e 'for(1..3){my $i if 1; print $i++, "\n"}'
0
0
0

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Re^2: Lexical scope variable is not undef'ed
by ikegami (Patriarch) on Oct 22, 2007 at 16:53 UTC

    That's not true. It's not parsed as if (0) { my $var = ''; }, and it does create a lexical $i (my's compile-time effect). 

    >perl -le "$::i=q{Pass }; for(1..3){my $i if 0; ++$i; print $::i, $i}"
Pass 1
Pass 2
Pass 3

>perl -le "$::i=q{Pass }; for(1..3){            ++$i; print $::i, $i}"
11
22
33

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    What happens is that the clearing doesn't occur at the end of the scope (my's run-time effect). See Re: Lexical scope variable is not undef'ed.

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