Runtime Extension of Ruby's World: require

By far the most important tool for getting a program in one file to see what's in other program files is the require method.

At its simplest, require causes a running program to pull in, and evaluate, the code from a file on disk. You can try this out easily. You need to create two files. Call the first req.rb, and put these lines in it:

def speak
  puts "Hello."
end

The second file should be called reqtest.rb, and its contents should be this:

require 'req'    # leave off the .rb extension
speak

Now test reqtest.rb. It's the top-level script, but when the interpreter runs it, both files are consulted.

% ruby reqtest.rb
Hello

As you can see, the require line in reqtest.rb caused the code in req.rb to ...

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