Status code 0 and stdout message on error

[kentakayama]

As cbor-diag tool becomes useful, I create CBOR binary from diagnostic notation and bring it to the automated processes.
When I make some mistakes, however, some commands such as diag2cbor.rb return status code 0 and print the error cause to stdout.
Thus these example commands seem success but the actual error messages are inside output cbor files.

$ echo "[]," | diag2cbor.rb > tailcomma.cbor
$ echo $?
0
$ cat tailcomma.cbor
*** can't parse [],
*** Expected one of [ \t\n\r], "/", '"', '{', '[', [0-9], [-+], '0', 'Infinity', '-Infinity', 'NaN', 'false', 'true', 'null', 'undefined', 'simple(', "h'", "'", "b64'", [a-z], "<<", '(' at line 2, column 1 (byte 5) after ,

$ echo "[0:1]" | diag2cbor.rb > colon_in_array.cbor
$ echo $?
0
$ cat colon_in_array.cbor
*** can't parse [0:1]
*** Expected one of [0-9], '(', [xX], [oO], [bB], '.', [Ee], [ \t\n\r], "/", ',', ']' at line 1, column 3 (byte 3) after [0

Can we change them to return non-zero value and to print error messages to stderr?