Really Cheap Command-Line Option Parsing in Ruby

Question

EDIT: Please, please, please read the two requirements listed at the bottom of this post before replying. People keep posting their new gems and li

Answer 1

Here's the code snippet I use at the top of most of my scripts:

arghash = Hash.new.tap { |h| # Parse ARGV into a hash
    i = -1                      
    ARGV.map{  |s| /(-[a-zA-Z_-])?([^=]+)?(=)?(.+)?/m.match(s).to_a }
     .each{ |(_,a,b,c,d)| h[ a ? "#{a}#{b}#{c}" : (i+=1) ] =
                             (a ? (c ? "#{d}" : true) : "#{b}#{c}#{d}") 
          }
    [[:argc,Proc.new  {|| h.count{|(k,_)| !k.is_a?(String)}}],
     [:switches, Proc.new {|| h.keys.select{|k| k[0] == '-' }}]
    ].each{|(n,p)| h.define_singleton_method(n,&p) }
}

I also hate to require additional files in my quick-and-dirty scripts. My solution is very nearly what you're asking for. I paste a 10 line snippet of code at the top of any of my scripts that parses the command line and sticks positional args and switches into a Hash object (usually assigned to a object that I've named arghash in the examples below).

Here's an example command line you might want to parse...

./myexampleprog.rb -s -x=15 --longswitch arg1 --longswitch2=val1 arg2

Which would become a Hash like this.

 { 
   '-s' => true, 
   '-x=' => '15', 
   '--longswitch' => true, 
   '--longswitch2=' => 'val1', 
   0 => 'arg1', 
   1 => 'arg2'
 }

In addition to that, two convenience methods are added to the Hash:

• argc() will return the count of non-switch arguments.
• switches() will return an array containing the keys for switches that are present

This is mean to allow some quick and dirty stuff like...

• Validate I've got the right number of positional arguments regardless of the switches passed in ( arghash.argc == 2 )
• Access positional arguments by their relative position, regardless of switches appearing before or interspersed with positional arguments ( e.g. arghash[1] always gets the second non-switch argument).
• Support value-assigned switches in the command line such as "--max=15" which can be accessed by arghash['--max='] which yields a value of '15' given the example command line.
• Test for the presence or absence of a switch in the command line using a very simple notation such as arghash['-s'] which evaluates to true if it's present and nil if its absent.

• Test for the presence of a switch or alternatives of switches using set operations like

  puts USAGETEXT if !(%w(-h --help) & arghash.switches()).empty?

• Identify use of invalid switches using set operations such as

  puts "Invalid switch found!" if !(arghash.switches - %w(-valid1 -valid2)).empty?

• Specify default values for missing arguments using a simple Hash.merge() such as the below example that fills in a value for -max= if one was not set and adds a 4th positional argument if one was not passed.

  with_defaults = {'-max=' => 20, 3 => 'default.txt'}.merge(arghash)