Ruby: Require VS Require_Relative - Best Practice to Workaround Running in Both Ruby ≪1.9.2 and ≫=1.9.2

Requiring files in Ruby

require_relative 'lib/checkers/board'
require_relative 'lib/checkers/checker'

This is how I have always done it. This is located in my main app file, which is always in the root directory. I'm unsure how it will behave from other files, although I believe it will be relative to the calling file.

Also, settings.root will return the root directory of your app, no need for File.dirname(__FILE__) anywhere.

This works in Ruby 1.9 without any special techniques via the comments above.

If you are using 1.8, you can do this

require './lib/checkers/board'
require './lib/checkers/checker'

Other techniques for 1.8 are listed in this question.

Why does Ruby 1.9.2 remove . from LOAD_PATH, and what's the alternative?

It was deemed a "security" risk.

You can get around it by using absolute paths

File.expand_path(__FILE__) et al

or doing

require './filename' (ironically).

or by using

require_relative 'filename'

or adding an "include" directory

ruby -I . ...

or the same, using irb;

$irb -I .

Calling another ruby file that is not a gem

In 99% of all cases when a computer tells you that it couldn't find a thing, it is because the thing isn't there. So, the first thing you need to check is whether there actually is a file named TestClass.rb somewhere on your filesystem.

In 99% of the rest of the cases, the computer is looking in the wrong place. (Well, actually, the computer is usually looking in the right place, but the thing it is looking for is in the wrong place). require loads a file from the $LOAD_PATH, so you have to make sure that the directory that the file TestClass.rb is in actually is on the $LOAD_PATH.

Alternatively, if you do not want to require a file from the $LOAD_PATH but rather relative to the position of the file that is doing the requireing, then you need to use require_relative.

Note, however, that your code won't work anyway, since say_hello is in instance method of instances of the TestClass class, but you are calling it on the main object, which is an instance of Object, not TestClass.

Note also that standard naming conventions of Ruby files are snake_case, in particular, the snake_case version of the primary class/module of the file. So, in your case, the file should be named test_class.rb. Also, require and require_relative figure out the correct file extension for themselves, so you should leave off the .rb. And thirdly, standard Ruby coding style is two spaces for indentation, not four.

None of these will lead to your code not working, of course, since it is purely stylistic, but it may lead to people being unwilling to answer your questions, since it shows that you don't respect their community enough to learn even the most basic rules.

Ruby require error

Ruby 1.9.2 does not include the current file's directory in $LOAD_PATH.

You can try using require_relative instead:

require_relative 'cpu.rb'

Or you can supply the actual path:

require './cpu.rb'

Or you can add the current file's directory to the load path:

$LOAD_PATH.unshift File.dirname(__FILE__)
require 'cpu.rb'

How do you specify a required switch (not argument) with Ruby OptionParser?

I am assuming you are using optparse here, although the same technique will work for other option parsing libraries.

The simplest method is probably to parse the parameters using your chosen option parsing library and then raise an OptionParser::MissingArgument Exception if the value of host is nil.

The following code illustrates

#!/usr/bin/env ruby
require 'optparse'

options = {}

optparse = OptionParser.new do |opts|
  opts.on('-h', '--host HOSTNAME', "Mandatory Host Name") do |f|
    options[:host] = f
  end
end

optparse.parse!

#Now raise an exception if we have not found a host option
raise OptionParser::MissingArgument if options[:host].nil?


puts "Host = #{options[:host]}"

Running this example with a command line of

./program -h somehost

simple displays "Host = somehost"

Whilst running with a missing -h and no file name produces the following output

./program:15: missing argument:  (OptionParser::MissingArgument)

And running with a command line of ./program -h produces

/usr/lib/ruby/1.8/optparse.rb:451:in `parse': missing argument: -h (OptionParser::MissingArgument)
  from /usr/lib/ruby/1.8/optparse.rb:1288:in `parse_in_order'
  from /usr/lib/ruby/1.8/optparse.rb:1247:in `catch'
  from /usr/lib/ruby/1.8/optparse.rb:1247:in `parse_in_order'
  from /usr/lib/ruby/1.8/optparse.rb:1241:in `order!'
  from /usr/lib/ruby/1.8/optparse.rb:1332:in `permute!'
  from /usr/lib/ruby/1.8/optparse.rb:1353:in `parse!'
  from ./program:13

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