Parse multiple command line options in Ruby using OptionParser

Question

I've just started using OptionParser for Ruby and I wanted to use flags that would use more than just one argument.

For instance, I would like to be able to run:

script --move src dst

Note how src and dst are not separated using a coma.

My initial idea was:

opts.on("-m src dst", "--move src dst ", "move file from SRCto DST") do |src|
    # do something
end

But this is not working. I assume that this is not the right approach. But how could this be done?

There is very good example in documentation http://ruby-doc.org/stdlib-2.2.4/libdoc/optparse/rdoc/OptionParser.html under heading `Generating Help`, which shows how to accept a parameter called `name`. Same can be extended for your case of `src` and `dst`. You need to repeat what example shows for `name` - once for `src` and once for `dst` as two separate `opts.on` statements — Wand Maker, Dec 22 '15 at 13:28
OP is specifically asking how to accept two consecutive values for the same option. — Jordan Running, Dec 22 '15 at 16:37

score 3 · Answer 1 · edited May 23 '17 at 11:47

The example under the "Complete Example" section of the OptionParser details how a list of items can be accepted.

Here is a sample program based on that example. The third parameter Array in opts.on indicates that input src, dst should be used to create an array. To run this sample, you need to do gem install trollop.

# test.rb
require 'optparse'

options = {}
OptionParser.new do |opt|
  opt.on("-m src, dst", "--move src, dst", Array, "Move from src to dst") do |list|
    options[:src] = list[0]
    options[:dst] = list[1]
  end
end.parse!

puts options # It's a hash of parsed options

Sample run:

> ruby test.rb -m from,to
{:src=>"src", :dst=>"dst"}

>ruby test.rb -h
Usage: test [options]
    -m, --move src, dst              Move from src to dst

The above script forces one to separate the options using comma.

As indicated by "Really Cheap Command-Line Option Parsing in Ruby", there seems to be a gem, trollop, that can be quite easy to use for command-line parsing.

A sample program based on Trollop is given below, which allows usage of spaces for specifying options with multiple values

# test.rb

require "trollop"

opts = Trollop::options do
  banner "Command line parsing using Trollop"
  opt :move, "--move src dst', Move from src to dst", :short => "-m", :long => "--move", :type => :strings
end
# An array of option values
p opts.move

Sample run:

>ruby test.rb -m hello world
["hello", "world"]

>ruby test.rb -h
Command line parsing using Trollop
  -m, --move=<s+>    '--move src dst', Move from src to dst
  -h, --help         Show this message

There is a subtle difference between the help output between the two approaches. Trollop produces help text where --move=<s+> does not indicate clearly that it needs accepts two values, so I had to repeat the command syntax description.

Thank you very much, as of today I am using this format. Do you reckon that there is away to get rid of the comma? So, instead of --move src, dst... you could just write --move src dst... but cheers anyway :) — Daniel Hernandez, Dec 22 '15 at 17:24
I am trying to figure that out, if I discover something I will update the answer. I think `OptionParser#accept` method will play some role but documentation is bit weak in explaining the parameters of `accept` method — Wand Maker, Dec 22 '15 at 17:27

the Tin Man · Accepted Answer · 2015-12-22T22:47:11.927

OptionParser doesn't support that; It could be patched to do so, but I'm not sure it's worth the trouble.

Consider this code:

require 'optparse'

options = {}
OptionParser.new do |opt|
  opt.on('-m', '--move') { |o| options[:move] = o }
end.parse!

from_name, to_name = ARGV

puts "Should move: #{ options.key?(:move) }"
puts "From: #{ from_name }"
puts "To: #{ to_name }"

Saving it and running it with various combinations of the parameters returns:

> ruby test.rb --move from to
Should move: true
From: from
To: to

> ruby test.rb  from to
Should move: false
From:
To:

If the code is supposed to move files by default then don't bother with the --move flag, simply use:

test.rb from to

and consider removing the OptionParser block entirely.

If the code is supposed to normally copy with the option to move, then --move becomes more sensible to act as a flag that moving is desired.

ruby test.rb --move from to

I'd have code that tests for options[:move] and run the code to move instead of copy at that point.

In either case, the filenames shouldn't be tied to the flag, they should be supplied separately and retrieved from ARGV after OptionParser has finished parsing the command-line and removing entries it's handled.

Parse multiple command line options in Ruby using OptionParser

2 Answers2