Ruby script - does not print 'Hello world!' from the command line

Question

I have the following code in the script a.rb.

def main
  puts "Hello World!"
end

When I run ruby a.rb on the command line, it doesn't display anything.

Why is this happening?

Yu Hao · Accepted Answer · 2015-05-28 16:44:40Z

8

Unlike languages like C/C++/Java, Ruby does't have a main method that's called at program startup. The name main is not special.

You defined a method named main, but never call¹ it.

def main
  puts "Hello World!"
end

main # here, call the method

_{1: Technically, calling methods should be called sending messages, the idea comes from Smalltalk.}

edited May 28, 2015 at 16:44

answered May 28, 2015 at 15:03

Yu Hao

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2 Comments

Luke Over a year ago

For clarity, you don't have to define main at all if you don't want to. Your script could have one line containing simply: puts "Hello World!"

Jörg W Mittag Over a year ago

You defined a method called main, there are no functions in Ruby. Also, we don't talk about "calling methods" in Ruby, we talk about "sending messages".

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