Parse command line arguments in a Ruby script

Question

I want to call a Ruby script from the command line, and pass in parameters that are key/value pairs.

Command line call:

$ ruby my_script.rb --first_name=donald --last_name=knuth

my_script.rb:

puts args.first_name + args.last_name

What is the standard Ruby way to do this? In other languages I usually have to use an option parser. In Ruby I saw we have ARGF.read, but that does not seem to work key/value pairs like in this example.

OptionParser looks promising, but I can't tell if it actually supports this case.

Answer 1

Here is a slight modification to @Phrogz excellent answer: this mod will allow you to pass a string with spaces in it.

args= Hash[ ARGV.join(' ').scan(/--?([^=\s]+)(?:="(.*?)"+)?/)]

In a command line pass the string like this:

ruby my_script.rb '--first="Boo Boo" --last="Bear"'

Or from another ruby script like this:

system('ruby my_script.rb \'--first="Boo Boo" --last="Bear"\'')

Results:

{"first"=>"Boo Boo", "last"=>"Bear"}

Answer 2

Ruby's built-in OptionParser does this nicely. Combine it with OpenStruct and you're home free:

require 'optparse'

options = {}
OptionParser.new do |opt|
  opt.on('--first_name FIRSTNAME') { |o| options[:first_name] = o }
  opt.on('--last_name LASTNAME') { |o| options[:last_name] = o }
end.parse!

puts options

options will contain the parameters and values as a hash.

Saving and running that at the command line with no parameters results in:

$ ruby test.rb
{}

Running it with parameters:

$ ruby test.rb --first_name=foo --last_name=bar
{:first_name=>"foo", :last_name=>"bar"}

That example is using a Hash to contain the options, but you can use an OpenStruct which will result in usage like your request:

require 'optparse'
require 'ostruct'

options = OpenStruct.new
OptionParser.new do |opt|
  opt.on('-f', '--first_name FIRSTNAME', 'The first name') { |o| options.first_name = o }
  opt.on('-l', '--last_name LASTNAME', 'The last name') { |o| options.last_name = o }
end.parse!

puts options.first_name + ' ' + options.last_name

$ ruby test.rb --first_name=foo --last_name=bar
foo bar

It even automatically creates your -h or --help option:

$ ruby test.rb -h
Usage: test [options]
        --first_name FIRSTNAME
        --last_name LASTNAME

You can use short flags too:

require 'optparse'

options = {}
OptionParser.new do |opt|
  opt.on('-f', '--first_name FIRSTNAME') { |o| options[:first_name] = o }
  opt.on('-l', '--last_name LASTNAME') { |o| options[:last_name] = o }
end.parse!

puts options

Running that through its paces:

$ ruby test.rb -h
Usage: test [options]
    -f, --first_name FIRSTNAME
    -l, --last_name LASTNAME
$ ruby test.rb -f foo --l bar
{:first_name=>"foo", :last_name=>"bar"}

It's easy to add inline explanations for the options too:

OptionParser.new do |opt|
  opt.on('-f', '--first_name FIRSTNAME', 'The first name') { |o| options[:first_name] = o }
  opt.on('-l', '--last_name LASTNAME', 'The last name') { |o| options[:last_name] = o }
end.parse!

and:

$ ruby test.rb -h
Usage: test [options]
    -f, --first_name FIRSTNAME       The first name
    -l, --last_name LASTNAME         The last name

OptionParser also supports converting the parameter to a type, such as an Integer or an Array. Refer to the documentation for more examples and information.

You should also look at the related questions list to the right:

• "Really Cheap Command-Line Option Parsing in Ruby"
• "Pass variables to Ruby script via command line"

Answer 3

A bit of standard Ruby Regexp in myscript.rb:

args = {}

ARGV.each do |arg|
  match = /--(?<key>.*?)=(?<value>.*)/.match(arg)
  args[match[:key]] = match[:value] # e.g. args['first_name'] = 'donald'
end

puts args['first_name'] + ' ' + args['last_name']

And on the command line:

$ ruby script.rb --first_name=donald --last_name=knuth

Produces:

$ donald knuth

Answer 4

An improved version that handles arguments that are not options, arguments with a parameter, and -a as well as --a.

def parse(args)
  parsed = {}

  args.each do |arg|
    match = /^-?-(?<key>.*?)(=(?<value>.*)|)$/.match(arg)
    if match
      parsed[match[:key].to_sym] = match[:value]
    else
      parsed[:text] = "#{parsed[:text]} #{arg}".strip
    end
  end

  parsed
end

Answer 5

I personnaly use Docopt. This is much more clear, maintainable and esay-reading.

Have a look to online Ruby implementation doc for examples. Usage is really straightforward.

gem install docopt

Ruby code:

doc = <<DOCOPT
My program who says hello

Usage:
  #{__FILE__} --first_name=<first_name> --last_name=<last_name>
DOCOPT

begin
  args = Docopt::docopt(doc)
rescue Docopt::Exit => e
  puts e.message
  exit
end

print "Hello #{args['--first_name']} #{args['--last_name']}"

Then calling:

$ ./says_hello.rb --first_name=Homer --last_name=Simpsons
Hello Homer Simpsons

And without arguments :

$ ./says_hello.rb
Usage:
  says_hello.rb --first_name=<first_name> --last_name=<last_name>

Answer 6

Based on the answer by @MartinCortez here's a short one-off that makes a hash of key/value pairs, where the values must be joined with an = sign. It also supports flag arguments without values:

args = Hash[ ARGV.join(' ').scan(/--?([^=\s]+)(?:=(\S+))?/) ]

…or alternatively…

args = Hash[ ARGV.flat_map{|s| s.scan(/--?([^=\s]+)(?:=(\S+))?/) } ]

Called with -x=foo -h --jim=jam it returns {"x"=>"foo", "h"=>nil, "jim"=>"jam"} so you can do things like:

puts args['jim'] if args.key?('h')
#=> jam

---

While there are multiple libraries to handle this—including GetoptLong included with Ruby—I personally prefer to roll my own. Here's the pattern I use, which makes it reasonably generic, not tied to a specific usage format, and flexible enough to allow intermixed flags, options, and required arguments in various orders:

USAGE = <<ENDUSAGE
Usage:
   docubot [-h] [-v] [create [-s shell] [-f]] directory [-w writer] [-o output_file] [-n] [-l log_file]
ENDUSAGE

HELP = <<ENDHELP
   -h, --help       Show this help.
   -v, --version    Show the version number (#{DocuBot::VERSION}).
   create           Create a starter directory filled with example files;
                    also copies the template for easy modification, if desired.
   -s, --shell      The shell to copy from.
                    Available shells: #{DocuBot::SHELLS.join(', ')}
   -f, --force      Force create over an existing directory,
                    deleting any existing files.
   -w, --writer     The output type to create [Defaults to 'chm']
                    Available writers: #{DocuBot::Writer::INSTALLED_WRITERS.join(', ')}
   -o, --output     The file or folder (depending on the writer) to create.
                    [Default value depends on the writer chosen.]
   -n, --nopreview  Disable automatic preview of .chm.
   -l, --logfile    Specify the filename to log to.

ENDHELP

ARGS = { :shell=>'default', :writer=>'chm' } # Setting default values
UNFLAGGED_ARGS = [ :directory ]              # Bare arguments (no flag)
next_arg = UNFLAGGED_ARGS.first
ARGV.each do |arg|
  case arg
    when '-h','--help'      then ARGS[:help]      = true
    when 'create'           then ARGS[:create]    = true
    when '-f','--force'     then ARGS[:force]     = true
    when '-n','--nopreview' then ARGS[:nopreview] = true
    when '-v','--version'   then ARGS[:version]   = true
    when '-s','--shell'     then next_arg = :shell
    when '-w','--writer'    then next_arg = :writer
    when '-o','--output'    then next_arg = :output
    when '-l','--logfile'   then next_arg = :logfile
    else
      if next_arg
        ARGS[next_arg] = arg
        UNFLAGGED_ARGS.delete( next_arg )
      end
      next_arg = UNFLAGGED_ARGS.first
  end
end

puts "DocuBot v#{DocuBot::VERSION}" if ARGS[:version]

if ARGS[:help] or !ARGS[:directory]
  puts USAGE unless ARGS[:version]
  puts HELP if ARGS[:help]
  exit
end

if ARGS[:logfile]
  $stdout.reopen( ARGS[:logfile], "w" )
  $stdout.sync = true
  $stderr.reopen( $stdout )
end

# etc.