$ perl -MO=Deparse,-p -le "while(<>){print}" BEGIN { $/ = "\n"; $\ = "\n"; } while (defined(($_ = ))) { print($_); } -e syntax OK $ perl -MO=Deparse,-p -le "while($f=<>){print}" BEGIN { $/ = "\n"; $\ = "\n"; } while (defined(($f = ))) { print($_); } -e syntax OK $ echo hi |perl -le "while($f=<>){print}"