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Ruby

Ruby basics

put it in header of every .rb file

#!/usr/bin/ruby -w

-w - verbose mode. If program file not specified, reads from STDIN.

Puts

Print some text.

Syntax:

puts "<some text>";

Example:

puts "Some text"

Multiple strings

print <<EOF # multiple line string
  This is the first way of creating
  here document ie. multiple line string.
EOF
print <<"EOF" # same as above
EOF
print<<`EOC` # execute commands
  echo hi there
  echo lo there
EOC
print <<"foo", <<"bar" # you can stack them
  I said foo.
foo
  I said bar.
bar

BEGIN statement

Declares code to be called before the program is run.

Syntax:

BEGIN {
  code
}

Example:

#!/usr/bin/ruby
puts "This is main Ruby Program"

BEGIN {
  puts "Initializing Ruby Program"
}

Result:

Initializing Ruby Program
This is main Ruby Program

END statement

Declares code to be called at the end of the program.

Syntax:

END {
  code
}

Example:

#!/usr/bin/ruby
puts "This is main Ruby Program"

END {
  puts "Terminating Ruby Program"
}
BEGIN {
  puts "Initializing Ruby Program"
}

Output:

Initializing Ruby Program
This is main Ruby Program
Terminating Ruby Program

Comments

# This is comment.
puts "Some code" # This is again comment.

= begin
This is a comment.
This is a comment, too.
= end

Classes and Objects

Defining a Class

Syntax:

class <class_name>
end

Variables in Class

  • Local Variables
    • Defined in a method. Local variables are not available outside the method.
    • Local variables begin with a lowercase letter or _.
  • Instance Variables
    • Instance variables are available across methods for any particular instance or object.
    • Instance variables are preceded by th at sign (@) followed by the variable name.
  • Class Variables
    • Class variables are available across different objects.
    • They are preceded by the sign @@ and are followed by the variable name.
  • Global Variables
    • The global variables are always preceded by the dollar sign ($).

Example:

class Customer
  @@no_of_customers = 0
end

Creating objects using new method

Syntax:

<variable_name> = <class_name>.new

Example:

foo = Foo.new

Custom method to create objects

You can pass parameters to method new and those parameters can be used to initialize class variables.

Example:

class Foo
  def initialize(foo, bar, baz)
    @foo = foo
    @bar = bar
    @baz = baz
  end

  foo = Foo.new("value_1", "value_2", "value_3")
  bar = Foo.new("value_1", "value_2", "value_3")
end

Member functions in Class

Syntax:

class <class_name>
  def <function_name>
  end
end

Example:

#!/usr/bin/ruby

class Foo
  def hello
    puts "Hello Ruby!"
  end
end

# Now using above class to create objects
foo = Foo.new
foo.hello

Output:

Hello Ruby!

Variables, Constants and Literals

Global variables

  • Global variables begin with $
  • Uninitialized global variables have the value nil and produce warnings with the -w option.

Example:

#!/usr/bin/ruby

$global_variable = 10

class Foo
  def print_global
    puts "Global variable in Foo is #$global_variable"
  end
end

class Bar
  def print_global
    puts "Global variable in Bar is #$global_variable"
  end
end

foo_obj = Foo.new
foo_obj.print_global

bar_obj = Bar.new
bar_obj.print_global

NOTE - In Ruby, you CAN access value of any variable or constant by putting a hash (#) character just before that variable or constant.

Result:

Global variable in Foo is 10
Global variable in Bar is 10