$ perl -wle'print 0+*STDOUT'
Argument "*main::STDOUT" isn't numeric in addition (+) at -e line 1.
0

$ perl -wle'print 0+*FOO'
Name "main::FOO" used only once: possible typo at -e line 1.
Argument "*main::FOO" isn't numeric in addition (+) at -e line 1.
0