Parsing arguments with defaults and flags.

Question

I've got a ruby bin with some arguments, namely -s, -c and -r (short for scrape, create and run). Now I'd like to set some defaults to scrape and create ('.' in both cases), but if I use :default in trollop, I can't check wherever that argument is set or not.

project --scrape

should be equivalent to

project --scrape .

how to achieve that?

And while at it, how do I make

project target

to be equivalent with

project --run target

?

Answer 1

You can modify ARGV before Trollop processes it. Your best bet would probably be to scan the input arguments, apply some basic transformations, and then run Trollop.

For example:

args = ARGV.split
idx = args.index '--scrape'
if idx != nil
    if idx < args.length
        if args[idx + 1][0..1] == '--'
            args=args[0..idx] + ['.'] + args[idx+1..-1]
        end
    else
        if args[idx + 1][0..1] == '--'
            args << '.'
        end
    end
end

This snippet should check for --scrape with no parameter following it and add in a '.' in that case. You can do something similar to check for the omitted --run parameter. When you are done making your modifications, use args.join(' ') to put the arguments back together into a string. Assign this new string to ARGV, and then set Trollop loose.