Introduction

Table of Contents

• Installation
• Hello World example
• Ruby REPL

From wikipedia)

Ruby is a dynamic, reflective, object-oriented, general-purpose programming language. It was designed and developed in the mid-1990s by Yukihiro "Matz" Matsumoto in Japan. According to the creator, Ruby was influenced by Perl, Smalltalk, Eiffel, Ada, and Lisp. It supports multiple programming paradigms, including functional, object-oriented, and imperative. It also has a dynamic type system and automatic memory management

Installation

• Get Ruby for your OS from official website - https://www.ruby-lang.org/en/downloads/
  • See installation guide for details, which also has info on tools like Ruby enVironment Manager (RVM)
• You can also try Ruby online
  • repl.it - programming environment for various languages including Ruby
  • tryruby - interactive tutorial that lets you try out Ruby right in your browser
• Examples presented here is for Unix-like systems, Ruby version 2.5.0p0 and uses bash shell
• It is assumed that you are familiar with command line. If not, check out this basic tutorial on ryanstutorials and this list of curated resources for Linux

Hello World example

• Let's start with simple a Ruby program and how to run it
• Use your favorite text editor to open a new file, type puts 'hello there!' and save the file as hello.rb
  • puts writes content of objects and adds a newline if not already present
  • in this example, it gets written to stdout
• Running it is as simple as invoking ruby command and passing hello.rb as argument

$ cat hello.rb
puts 'hello there!'

$ ruby hello.rb
hello there!

• An alternate way to run is using shebang)
• the # character indicates start of comment in Ruby
• if # is followed by ! in first line of the program, then it becomes a shebang

$ type env ruby
env is /usr/bin/env
ruby is /usr/local/bin/ruby

$ cat hello_world.rb
#!/usr/bin/env ruby

puts 'Hello World'

$ chmod +x hello_world.rb
$ ./hello_world.rb
Hello World

Further Reading

• ruby-doc: version 2.5.0
• ruby-doc: puts

Ruby REPL

• It is generally used to execute snippets of Ruby language as a means to learning Ruby or for debugging purposes
• Result of entered expression is displayed with a prefix =>
  • also, a special variable _ holds the result of last expression in the interactive session
• use exit to end the interactive session
• comments will be used within code snippets presented in this material to add relevant information

$ # puts always returns nil
$ irb
irb(main):001:0> puts 'hi'     
hi
=> nil
irb(main):002:0> exit

• irb can be customized in many ways, see document link for details
• here on, irb --simple-prompt will be used for simplicity

$ alias irb='irb --simple-prompt'

$ irb
>> num = 5
=> 5
>> num
=> 5
>> 3 + 4
=> 7
>> 12 + _
=> 19
>> exit

• Often, you'd want to re-use previous instructions or correct a mistake
• On Linux, you need to install the rb-readline extension module. Invoking irb after that will allow arrow keys for navigation, ctrl+r for search, etc
  • If you are not using environment manager like RVM, use gem install --user-install rb-readline

Further Reading

• ruby-doc: interactive Ruby
• pry
• stackoverflow - installing gems