In Perl 6 die when called with something other than an instance of an Exception will wrap it in an X::AdHoc and then throw it.

If you really want it to work more like Perl 5 you could do the following.

die "foo\n";

CATCH {
  when X::AdHoc {
    if .message.ends-with("\n") {
      note .message.chomp; # $*ERR.print( .message )
      exit 1;
    } else {
      .rethrow;
    }
  }
}
[download]

I would recommend against doing this as it could cause problems. For example you could set the environment variable RAKUDO_EXCEPTIONS_HANDLER to JSON, but the above would prevent it from intercepting the exception and outputting JSON.