Why turn warnings off? Turning them on (and autoflushing STDOUT and STDERR, so the output is in order) prints:

Useless use of private variable in void context at myscript.pl line 27
+.
factory: 'lulz'
eval:    'lulz'
factory: 'frunz'
Variable "$var" is not available at (eval 2) line 1.
Use of uninitialized value $var in concatenation (.) or string at (eva
+l 2) line 1.
eval:    ''
factory: 'lulz'
eval:    'lulz'
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In the first factory, you're using $var in an eval{} block... which is quite different from a string eval(). This isn't an interesting case, and works as you expected anyway.

The difference between your second and third examples is the supposedly useless (as perl tells you) statement $var. The compressed answer is that when you generate the closure in these latter cases, perl has no idea that you're making use of $var in your block, and so it sees no reason to include it in the closure.

After all, all perl sees is a string and some function call (to eval()). But when you explicitly make use of $var in your (third) factory, perl includes it in the closure - not because it knows you're going to need it, but because you included it. When the string eval is then evaluated, it finds $var in the third factory, but can't resolve it in the second factory.

To make sure it is clear what I am referencing from a closure, I always like to explicitly write out which variables I need for it... I'd write something like:

return sub{
   my ($code) = ($var);
   my $estr = "print \"eval:    '\$code'\n\"";
   eval $estr;
}
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