python - `if __name__ == '__main__'` equivalent in Ruby

104
votes

I am new to Ruby. I'm looking to import functions from a module that contains a tool I want to continue using separately. In Python I would simply do this:

def a():
    ...
def b():
    ...
if __name__ == '__main__':
    a()
    b()

This allows me to run the program or import it as a module to use a() and/or b() separately. What's the equivalent paradigm in Ruby?

3
pythonrubymain
possible duplicate of Run a Ruby library from the command-line – Andrew Grimm

3 Answers

138
votes

From the Ruby I've seen out in the wild (granted, not a ton), this is not a standard Ruby design pattern. Modules and scripts are supposed to stay separate, so I wouldn't be surprised if there isn't really a good, clean way of doing this.

EDIT: Found it.

if __FILE__ == $0
    foo()
    bar()
end

But it's definitely not common.

12
votes

If stack trace is empty, we can start executing to the right and left. I don't know if that's used conventionally or unconventionally since I'm into Ruby for about a week. 

if caller.length == 0
  # do stuff
end

Proof of concept:

file: test.rb

#!/usr/bin/ruby                                                                 

if caller.length == 0
  puts "Main script"
end

puts "Test"

file: shmest.rb

#!/usr/bin/ruby -I .                                                            

require 'test.rb'

puts "Shmest"

Usage:

$ ./shmest.rb 
Test
Shmest

$ ./test.rb
Main script
Test
8
votes
if $PROGRAM_NAME == __FILE__
  foo()
  bar()
end

is preferred by Rubocop over this:

if __FILE__ == $0
    foo()
    bar()
end