Call ruby function from command-line

How can I directly call a ruby function from the command-line?

Imagine, I would have this script test.rb:

class TestClass
    def self.test_function(some_var)
        puts "I got the following variable: #{some_var}"
    end
end

If this script is run from the command-line (ruby test.rb), nothing happens (as intended).

Is there something like ruby test.rb TestClass.test_function('someTextString')? I want to get the following output: I got the following variable: someTextString.

Solution 1:

First the name of the class needs to start with a capital letter, and since you really want to use a static method, the function name definition needs to start with self..

class TestClass
    def self.test_function(someVar)
        puts "I got the following variable: " + someVar
    end
end

Then to invoke that from the command line you can do:

ruby -r "./test.rb" -e "TestClass.test_function 'hi'"

If you instead had test_function as an instance method, you'd have:

class TestClass
    def test_function(someVar)
        puts "I got the following variable: " + someVar
    end
end

then you'd invoke it with:

ruby -r "./test.rb" -e "TestClass.new.test_function 'hi'"

Solution 2:

Here's another variation, if you find that typing ruby syntax at the command line is awkward and you really just want to pass args to ruby. Here's test.rb:

#!/usr/bin/env ruby

class TestClass
  def self.test_function(some_var)
    puts "I got the following variable: #{some_var}"
  end
end

TestClass.test_function(ARGV[0])

Make test.rb executable and run it like this:

./test.rb "Some Value"

Or run it like this:

ruby test.rb "Some Value"

This works because ruby automatically sets the ARGV array to the arguments passed to the script. You could use ARGV[0] or ARGV.first to get the first argument, or you could combine the args into a single string, separated by spaces, using ARGV.join(' ').

If you're doing lots of command-line stuff, you may eventually have a use for Shellwords, which is in the standard ruby lib.