Grammar for Unix command line options

Question

This is a homework question. I would like to write a simple parser for Unix command line options.
First, I would like to define a grammar with BNF.

Options = Option | Options, space, Option;
Option = OptionName | OptionName, OptionArguments; 
OptionName = '--', any character excluding '-' | OptionName, any character;
OptionArguments = OptionArgument | OptionArguments, space, OptionArgument;
OptionArgument = any character excluding '-' | OptionArgument, any character;

("any character" here is any alphanumeric character).

Does it make sense ? The next question is how to add "old" Unix options, which start with a single hyphen and can be grouped together (e.g. ls -lht)

@khachik: he isn't excluding it, he's only excluding it in the first occurrence. Although it may appear in the first occurrence indeed. — Ryan Li, Dec 11 '10 at 13:37

score 3 · Answer 1 · answered Apr 12 '12 at 08:17

Just notice that the given grammar is quite ambiguous - for example, if you have a few words in a row, you wouldn't know if these are different options or an option with some arguments.

As for your second question (regarding "old" unix), you could add another rule to the grammar, something of the sort:

option -> optionGroup | (anything that was there before);
optionGroup -> '-', flags;
flags -> flag | flag, flags;
flag -> single letter;

Grammar for Unix command line options

1 Answers1