$ perl -MO=Deparse -e 'while (<>) { /(.)/ }'
while (defined($_ = readline ARGV)) {
    /(.)/;
}
-e syntax OK

$ perl -MO=Deparse -e 'while (my $line = <>) { $line =~ /(.)/ }' 
while (defined(my $line = readline ARGV)) {
    do {
        $line =~ /(.)/
    };
}
-e syntax OK