Revision as of 19:41, 12 August 2012

Ruby is an interpreted language, dynamically, reflective, semi-Functional and Object Orientated scripting language written in C. Ruby is said to be semi-Functional because it supports higher-order functions (aka lambdas) and closures (aka blocks). Ruby was created by Yukihiro "Matz" Matsumoto and was first released in 1995.

Matz's goal was to combine powerful features from various other programming languages, and create a programming language maximized for developer happiness; as opposed to computational efficiency. Ruby's Object Model mirrors that of Smalltalk, the syntax shares some similarities with Bash, Perl, Python, and the scoping rules for closures was taken from LISP.

Basics

Development Environment

• Installation
• Gems

Interactive Ruby Interpreter

IRB, or the Interactive Ruby Interpreter, comes bundled with Ruby and allows you to interactively run code right from your command line. IRB can be invoked from your terminal simply by typing 'irb'.

» irb --help
Usage:  irb.rb [options] [programfile] [arguments]
  -f		    Suppress read of ~/.irbrc 
  -m		    Bc mode (load mathn, fraction or matrix are available)
  -d                Set $DEBUG to true (same as `ruby -d')
  -r load-module    Same as `ruby -r'
  -I path           Specify $LOAD_PATH directory
  --inspect	    Use `inspect' for output (default except for bc mode)
  --noinspect	    Don't use inspect for output
  --readline	    Use Readline extension module
  --noreadline	    Don't use Readline extension module
  --prompt prompt-mode
  --prompt-mode prompt-mode
		    Switch prompt mode. Pre-defined prompt modes are
		    `default', `simple', `xmp' and `inf-ruby'
  --inf-ruby-mode   Use prompt appropriate for inf-ruby-mode on emacs. 
		    Suppresses --readline. 
  --simple-prompt   Simple prompt mode
  --noprompt	    No prompt mode
  --tracer	    Display trace for each execution of commands.
  --back-trace-limit n
		    Display backtrace top n and tail n. The default
		    value is 16. 
  --irb_debug n	    Set internal debug level to n (not for popular use)
  -v, --version	    Print the version of irb

» irb
irb(main):001:0> puts 'woot'
woot
=> nil
irb(main):002:0> 

Running irb --simple-prompt will provide you with a more basic looking Ruby shell.

» irb --simple-prompt
>> puts 'woot'
woot
=> nil
>> 

You can use either 'exit', 'quit', or 'irb_exit' to close IRB and return to your terminal.

<pre>
» irb --simple-prompt
>> exit
» # back in our terminal :D

Your first program

Code

#!/usr/bin/ruby
puts "Hello world\n"

Explanation

Variables and Data Types

Local

A local variable is a variable that can only be used within the block it was initialized in. It can be created by making an object that starts with a lowercase letter or an underscore.

 
foo = 'bar'
 

Global

Global variables can be accessed from anywhere within the entire program. They can be created by prefixing your variable the the '$' symbol. Editting the assignment of a global variable will change the status of that variable globally and is generally avoided when writing Ruby scripts.

 
$woot = 1337
 

Instance

Instance variables begin with the '@' symbol. Creating an uninitialzed instance will have a nil value.

>> @instance
=> nil
>> @instance = 'ohdae'
=> "ohdae"

Class

Class variables are shared by all methods within that class. These are created by using two '@' symbols at the beginning of your variable. Trying to initialize a class variable outside of a class will throw an error.

>> @@classvar
NameError: uninitialized class variable @@classvar in Object
	from (irb):5
	from :0
>> class Blackhat
>>   @@classvar = 'ohhai'

Pre-defined

Certain variables are pre-defined into Ruby. The values of these variables cannot be changed.

 
self
nil
true
false
 

Scalars

Arrays

An array is a group of objects, very similar to lists in Python. The items or objects inside an array are indexed on a non-negative zero-index. The objects inside of a Ruby array can be any mixture of variables. Creating an array can be done in a few different ways. You do not need to specifically declare your variable as an array during initialization, for example if you give Ruby a list of comma separated values inside brackets, Ruby will recgonize this as an array and use it as such from that point forward.

>> my_array = Array.new
=> []
>> my_array_two = []
=> []
>> array_three = ["item", 5, foo, "Item2", "Strings can go here too"]
=> ["item", 5, "bar", "Item2", "Strings can go here too"]
>> array_three[0]
=> "item"
>> array_three[1]
=> 5

You will notice the item 'foo' is printed as "bar" because we defined this earlier in this page.

Hashes or Associative Arrays

References and Pointers

Casting

.to_i
.to_s

Boolean Logic

Operators

Statements

Helper natives

Bitwise Manipulations

Loops

While

Until

For

Iterators

User Input

CGI & Eruby

Eruby has the same functionality as ruby with the added advantage of short tags from PHP. For example:

 
<html>
<head>
    <title>Test</title>
</head>
<body>
  <% 
      puts "Hello<br>"
  %>
</body>
</html>
 

Command-line Options

STDIN / Standard Input

User-defined

Functions

simple hello world function

 
 
def hello_world
  puts 'Hello, World!'
end
 

When calling a function that takes an argument, the parenthesis around the argument is optional.

 
def hello(name)
  puts 'Hello, #{name}!"
end
 
hello('ohdae')
=> Hello, ohdae!
hello 'ohdae'
=> Hello, ohdae!

function with default arguments

 
def hello(name='ohdae')
  puts 'Hello, #{name}!"
end
 
hello
=> Hello, ohdae!
hello 'world'
=> Hello, world!

• Return values

 
def add(arg1, arg2) 
    return nil unless defined? arg1
    return nil unless defined? arg2
    total = arg1.to_i + arg2.to_i
    return total
end

Objects

In ruby, class objects have names which must start in capital letters.

 
class MyClass
 
end
 

The constructor function is called initialize:

 
class MyClass
    def initialize()
        puts "Hello\n"
    end
end
 

Helpful Libraries

USqlite

require 'sqlite'
class Usqlite
    attr_accessor :link, :config, :a_rows, :rows, :result, :data
    def initialize(config, *args) 
        return nil unless defined? config
        @config = config
        @link = SQLite::Database.new(@config["sqlitefile"]) or exit("cannot open sqlite database")
    end
    def queryItem(query)
        return @link.get_first_value(query)
    end
    def queryRow(query)
        @link.results_as_hash = true
        @link.execute(query) do |row|
            @data = row
            return row
        end
    end
    def sqlQuery(query)
        @result = @link.query(query)
    end
    def sqlFetch() 
        @link.results_as_hash = true
        return @data if (@data = @results.next)
    end
    def sqlInsert(query)
        @a_rows = 0
        @link.query(query) do |result|
           @a_rows++
           result.next
        end
    end
end
 

Extensions

Programming extensions

Helpful extensions

Gems