Ruby

Ruby is an object oriented scripting language. Ruby is of particular interest because of the popular framework Ruby on Rails

irb --simple-prompt

ri ClassName
ri ClassName#method_name

Use the ARGV array:

ARGV[0]

invar = gets
# Getting rid of the newline
invar.chomp

Blocks of code can either be defined using curly brackets {}, or on multiple lines using the end keyword to terminate the block e.g.

def something
  ...
 end

continue them with a backslash \

• Variables start with a lower case letter
• Constants start with an upper case letter. They are usually all upper case
• Classes are capitalized

if myvar == "something"
  ..
elsif myvar == "somethingelse"
  ..
else
  ..
end

10.times do
  puts "hello"
end

while condition 
  ..
end

== !- < > ⇐ >=

Inside a quoted string, use curly braces and a hash e.g.

"This is a string with some #{variable} in it.

Use a template with a %s symbol, then you can reuse it later:

template = "This is a template where %s will be substituted"
puts template % "subsituted string"

Or with multiple substitutions:

template = "There are multiple strings here like %s and %s"
puts template % ["one","two"]

array_name = ["first", "second", "third"]
array_name = %w("one two three four five")
array_name[4] = "forth"

array_name.length
array_name.reverse
array_name.sort
array_name.include? element

multi_array = [[1,"one"],[2,"two"]]

array_name.each do |element|
  ...
end

hash_name = {
  "key1" => "value1",
  "key2" => "value2",
  "key3" => "value3",
}

hash_name.each do |key, value|
  ...
end

def some_function { puts “print it!” }

Similarly to other scripting languages, the eval command causes the interpreter to execute a string:

eval "puts 'Hello World!'"

def some_function

yield # where the code block is substituted

end

You can convert a block to an object. This preserves the current execution environment. The object is known as a proc. One way of doing this is using the lambda function.

p = lambda { |somevar| puts "somevar" + somevar }
p.call

Defining Classes:

class <ClassName>
  def initialize(somevar)
    @attrib =  attrib
  end
end

c_instance = ClassName.new

The null object in Ruby is called nil

Dir.open("some/path/").each do |dir|
  next if ["..","."].include? dir # Skip . and ..
  puts dir # Or some other operation
end

FileTest.exist?(file_name)

Dir.mkdir(directory_name) unless File.directory?(directory_name)

file_handle = File.open("file_name", "a")
file_handle.puts "some string"
file_handle.close

TK, the graphics toolkit that is normally used in TCL can also be called from Ruby

require 'tk'
app = TkRoot.new
TkLabel.new(app) do
  text "Hellow World!"
end
Tk.mainloop