$ perl -le '$_ = ($x) = (4, 5, 6); print'
3

$ perl -le '($_ = ($x = (4, 5, 6))); print($_)'
6

$ perl -MO=Deparse,-p -le '$_ = ($x) = (4, 5, 6); print'
BEGIN { $/ = "\n"; $\ = "\n"; }
($_ = (($x) = (4, 5, 6)));
print($_);
-e syntax OK


$ perl -v
 
This is perl, v5.8.3 built for i586-linux-thread-multi