🚀 go-pugleaf

Suppose that I am writing a utility

utility [-mode1 <24|124>] [-mode2 [67]]

so if I am correct in using the BNF notation, [] denotes optional arguments
and <> denotes mandatory arguments. The command egrep in linux has alternate
patterns for searching specified by the vertical stroke, "|" as we have used
for mode number one for this utility. I have used numbers as the arguments
to the switches to show this possibility.

I have to parse this command line via *argv[] and argc.
Please show how to approach it. For example, what argc will different
arguments give? 

utility -mode1 "24|214"
utility -mode1  24|214
utility -mode2  24
utility -mode2 "24" -mode2 67

and how will we deal with conflicting arguments? Is there are uniform and
professional method of approaching this problem? I am not a CS and hardly
know the finite state machines but if you are kind enough to put some examples
to plant the ideas, would be very grateful and finish this work. I do have
the dragon book.

I am posting this to C/C++ because they are the languages of implementation
and unix because they also deal with it and GNU compatible utilities require
robust and unambiguous command line interface as a basic requirement to 
consider any to be considered gnuable.

Thanks a lot for any help and hope to give you some good utilities in return!!!