Chahdi - Ruby Notes for Professionals: Ruby Programmation step by step

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Version Release Date
2.5.1 2018-03-28
2.4 2016-12-25
2.3 2015-12-25
2.2 2014-12-25
2.1 2013-12-25
2.0 2013-02-24
1.9 2007-12-25
1.8 2003-08-04
1.6.8 2002-12-24

This example assumes Ruby is installed.
Place the following in a file named hello.rb :
puts 'Hello World'
From the command line, type the following command to execute the Ruby code from the source file:
$ ruby hello.rb
This should output:
Hello World
The output will be immediately displayed to the console. Ruby source files don't need to be compiled before being executed. The Ruby interpreter compiles and executes the Ruby file at runtime. You can add an interpreter directive (shebang) to your script. Create a file called hello_world.rb which contains:
#!/usr/bin/env ruby
puts 'Hello World!'
Give the script executable permissions. Here's how to do that in Unix:
$ chmod u+ x hello_world.rb
Now you do not need to call the Ruby interpreter explicitly to run your script. $ ./ hello_world.rb Alternatively, you can use the Interactive Ruby Shell (IRB) to immediately execute the Ruby statements you previously wrote in the Ruby file.
Start an IRB session by typing:
$ irb
Then enter the following command:
puts "Hello World"
This results in the following console output (including newline):
Hello World
If you don't want to start a new line, you can use print :
print "Hello World" Run the command below in a shell after installing Ruby. This shows how you can execute simple Ruby programs without creating a Ruby file:
ruby - e 'puts "Hello World"'
You can also feed a Ruby program to the interpreter's standard input. One way to do that is to use a here document in your shell command:

ruby
END

Tk is the standard graphical user interface (GUI) for Ruby. It provides a cross-platform GUI for Ruby programs.
Example code:

require "tk"
TkRoot.new { title "Hello World!" }
Tk.mainloop

The result:
Step by Step explanation:
require "tk"
Load the tk package.
TkRoot.new { title "Hello World!" }
Define a widget with the title Hello World
Tk.mainloop
Start the main loop and display the widget. Overview
Create a new file named my_first_method.rb
Place the following code inside the file:

def hello_world
puts "Hello world!"
end

hello_world()# or just 'hello_world' (without parenthesis)
Now, from a command line, execute the following:
ruby my_first_method.rb
The output should be:
Hello world!
Explanation

def is a keyword that tells us that we're def -ining a method - in this case, hello_world is the name of our method.
puts "Hello world!" puts (or pipes to the console) the string Hello world!
end is a keyword that signifies we're ending our definition of the hello_world method as the hello_world method doesn't accept any arguments, you can omit the parenthesis by invoking the method

"123.50" .to_f #=> 123.5
Float ( "123.50" )#=> 123.5
However, there is a difference when the string is not a valid Float :
"something" .to_f #=> 0.0
Float ( "something" )# ArgumentError: invalid value for Float(): "something" 123.5 .to_s #=> "123.5"
String ( 123.5 )#=> "123.5"
Usually, String () will just call #to_s .
Methods Kernel#sprintf and String#% behave similar to C:

sprintf ( "%s" , 123.5 )#=> "123.5"
"%s" % 123.5 #=> "123.5"
"%d" % 123.5 #=> "123"
"%.2f" % 123.5 #=> "123.50"

"123.50" .to_i #=> 123
Integer ( "123.50" )#=> 123
A string will take the value of any integer at its start, but will not take integers from anywhere else:
"123-foo" .to_i # => 123
"foo-123" .to_i # => 0
However, there is a difference when the string is not a valid Integer:
"something" .to_i #=> 0
Integer ( "something" )# ArgumentError: invalid value for Integer(): "something"