$ perl -le'open $fh, "<", "foo"; print for PerlIO::get_layers($fh)'
unix
perlio

$ perl -le'open $fh, "<", "foo"; binmode $fh; print for PerlIO::get_layers($fh)'
unix
perlio

$ perl -le'open $fh, "<", "foo"; binmode $fh, ":raw"; print for PerlIO::get_layers($fh)'
unix
perlio

$ perl -le'open $fh, "<:raw", "foo"; print for PerlIO::get_layers($fh)'
unix