Hello World (Ruby)

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This is a simple Ruby program that prints a string to the console, then prints the integers 1 through 10 using a simple for loop.

<<hello_world.rb>>=
print greeting
print first ten integers

Printing a greeting is as simple as

<<print greeting>>=
puts "Hello World!"

Ruby has a for-loop so print first ten integers can be implemented (using a range) like this:

for i in 1..10
  puts i
end

But the use of an iterator and a closure is more idiomatic:

<<print first ten integers>>=
(1..10).each { |i|
  puts i
}

Ruby is a scripting language so there is no compiler. To run the program you simply fire up the ruby interpreter and pass it the script:

$ ruby hello_world.rb
Hello World!
1
2
3
4
5
6
7
8
9
10

Ruby is also an object-oriented language which contains classes. The hello world program as a class would be

<<hello_world_class.rb>>=
class HelloWorld
  def greet()
     print greeting
  end
  def printFirstTenIntegers()
     print first ten integers
  end
end

The class can be loaded, instantiated and executed inside the interpreter like this:

$ irb
irb(main):001:0> require 'hello_world_class.rb'
=> true
irb(main):002:0> hw = HelloWorld.new
=> #<HelloWorld:0x3ebe08>
irb(main):003:0> hw.greet
Hello World!
=> nil
irb(main):004:0> hw.printFirstTenIntegers
1
2
3
4
5
6
7
8
9
10
=> 1..10
irb(main):005:0>

or in a script, like this:

require 'hello_world_class.rb'
hw = HelloWorld.new
hw.greet
hw.printFirstTenIntegers

References

• First Edition of Programming Ruby (Online) by Dave Thomas and Andy Hunt (The Pragmatic Programmers).
• Wikipedia entry on the Ruby programming language

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