$ perl -wE 'say 0 + "1.2"' 1.2 $ perl -wE 'say 0 + "1.2.3"' Argument "1.2.3" isn't numeric in addition (+) at -e line 1. 1.2 #### $ perl -wE 'say 0 + !1' # no warning 0 $ perl -wE 'my $false = !1; say "<<$false>>"' # empty string! <<>>