Re^3: Why/how are these different?

[AnomalousMonk]

[Use of warnings] often gives an insight into what Perl understands your code to be. (Athanasius)

perl-diddler: Another path to insight is to have Perl deparse your code for you (see B::Deparse and O):

>perl -wMstrict -MO=Deparse,-p -le
"print qq{\$_ '$_'} for $_ = 3; $_-- >0;
"
Useless use of numeric gt (>) in void context at -e line 1.
BEGIN { $^W = 1; }
BEGIN { $/ = "\n"; $\ = "\n"; }
use strict 'refs';
print("\$_ '${_}'") foreach (($_ = 3));
(($_--) > 0);
-e syntax OK