Question

In my lib folder I have billede.rb:

class Billede
  require 'RMagick'
  #some code that creates a watermark for a image
  image.write(out)
end

How do I call/activate the class? Is the only way to change it to a Rake task?

Answer 1

Code ‘inside a class’ is run just like any other code. If you have a Ruby file like this:

puts "Hello from #{self}"
class Foo
  puts "Hello from #{self}"
end

and you run the file (either via ruby foo.rb on the command line or require "./foo" or load "foo.rb" in a script) it then you will see the output:

Hello from main
Hello from Foo

If you want to load a utility that ‘does something’ that you can then invoke from a REPL like IRB or the Rails console, then do this:

module MyStuff
  def self.do_it
    # your code here
  end
end

You can require "./mystuff" to load the code, and when you’re ready to run it type MyStuff.do_it

And, as you may guess, you can also create methods that accept arguments.

If you want to define a file that can be included in others (with no immediate side effects) but which also “does its thing” whenever the file is run by itself, you can do this:

module MyStuff
  def self.run!
    # Go
  end
end

MyStuff.run! if __FILE__==$0

Now if you require or load this file the run! method won’t be invoked, but if you type ruby mystuff.rb from the command line it will.