Option Parsing In Shell

A pattern for parsing options from the command line.

Having read ParamPattern, I think this can be done in a more general and flexible way.

I usually parse options from the command line in the following way:

 # Parse this function $@
 function parse_opts () 
 {
         # What to do if program is called with no parameters...
         if [ $# -eq 0 ]; then
                 handle_no_params # insert your own code here...
         fi

         # handle all parameters
         while [ "x$1" != "x" ]
         do
                 case x$1 in
                 x-v|x--version) display_version ;;
                 x-h|x--help) display_help ;;    # alternatively, use the Comments As Data pattern here...
                 *) ;;                              # Just ignore this unknown option...
         esac
         shift
         done
 }

 # do it!
 parse_opts $@

You then call parse_opts with $@ (all the argument from the command line). Note that you can easily handle different parameters in different places. It's perfectly possible to have several similar parse_opts functions handling different types of parameters, since the function works on a "copy" of $@ (you could use this in the ParamPattern scenario where you parse general options in a separate place).

The GNU getopt program is also a nice way to do it. It gives you a lot of control and flexibility. However, sometimes it's not available on the platform you're working on. The solution above relies only on shell builtins.

-- Christian Theil Have (cth @ dasfisk dot dk)

---

CategoryUnixShellPattern