linux GNU getopt: ignore unknown optional arguments?

Question

Is it possible to ignore unknown optional arguments with GNU getopt?

I have a script, scriptA.sh, that has optional arguments --optA, --optB, --optC, --optD.

I would like to write a wrapper, wrapperA, with two optional arguments, --optX and --optY, that calls scriptA. However, I don't want to declare all optional parameters of scriptA inside the wrapper.

In particular, if inside wrapperA, I specify optional arguments with

getopt --longoptions optX:,optY:

the call

wrapperA --optX --optA --optB

returns an error

getopt: unknown option -- optA

Can GNU getopt be forced to ignore unknown arguments and place them after the '--' in its output?

Answer 1

It is not possible to tell GNU getopt to ignore unknown options. If you really want that feature you will have to write your own option parser.

It is not as simple as to just ignore unknown options. How can you tell whether an unknown option takes an argument or not?

Example usage of original script:

originalscript --mode foo source

here foo is an argument to the option --mode. while source is a "non-option parameter" (sometimes called "positional parameter").

Example usage of wrapper script:

wrapperscript --with template --mode foo source

How can getopt in wrapperscript know that it should ignore --mode together with foo? If it just ignores --mode then originalscript will get foo as first positional parameter.

A possible workaround is to tell the users of your wrapper script to write all options intended for the original scrip after a double dash (--). By convention a double dash marks the end of options. GNU getopt recognizes double dash and stops parsing and returns the rest as positional parameters.

See also:

• http://wiki.bash-hackers.org/dict/terms/end_of_options

Answer 2

I was working on a similar thing, and found this to work to stop getopt errors from bugging me with these errors. Basically just pipe the errors to oblivion.

while getopts "i:s:" opt > /dev/null 2>&1; do
    case $opt in
      i)
        END=$OPTARG
      ;;
    esac
done
./innerscript $*

$ ./blah.sh -s 20140503 -i 3 -a -b -c