Basic Concepts

Ruby Keywords

Keywords or reserved words are special words in a programming language that have predefined meanings and are used for certain internal processes. These words cannot be used as identifiers such as variable names, object names, or constants. Attempting to use these reserved words as identifiers will result in a compile-time error.

Example of Invalid Use of Keywords

				
					# Ruby program to illustrate Keywords

# This is an incorrect use of the keyword 'if'
# It cannot be used as a variable name
if = 30

# Here 'if' and 'end' are keywords used incorrectly
# Using them will result in a syntax error
if if >= 18
  puts "You are eligible to drive."
end

Compile-Time Error:

				
					Error(s), warning(s):

example.rb:4: syntax error, unexpected '='

if = 30

    ^

example.rb:9: syntax error, unexpected '>='

if if >= 18

        ^

example.rb:11: syntax error, unexpected keyword_end, expecting end-of-input

Common Ruby Keywords

Ruby has a total of 41 reserved keywords. Here are some of the most common ones and their uses:

Keyword	Description
`__ENCODING__`	The script encoding of the current file.
`__LINE__`	The line number in the current file.
`__FILE__`	The path to the current file.
`BEGIN`	Runs code before any other in the current file.
`END`	Runs code after all other code in the current file.
`alias`	Creates an alias for a method.
`and`	Logical AND with lower precedence than `&&`.
`class`	Defines a new class.
`def`	Defines a method.
`do`	Begins a block of code.
`end`	Ends a syntax block such as a class, method, or loop.
`if`	Conditional statement.
`module`	Defines a module.
`next`	Skips to the next iteration of a loop.
`nil`	Represents “no value” or “undefined”.
`return`	Exits from a method and optionally returns a value.
`self`	Refers to the current object.
`true`	Boolean true value.
`while`	Creates a loop that executes while a condition is true.

Example of Using Keywords Correctly

Here’s a simple example demonstrating the correct use of some Ruby keywords:

				
					# Ruby program to illustrate the use of Keywords

#!/usr/bin/ruby

# Defining a class named 'Person'
class Person

  # Defining a method using 'def' keyword
  def introduce
    # Printing a statement using 'puts'
    puts "Hello! I'm learning Ruby."
  end

# End of the method
end

# End of the class
end

# Creating an object of the class 'Person'
student = Person.new

# Calling the method using the object
student.introduce

Output:

				
					Hello! I'm learning Ruby.

Ruby Data Types

In Ruby, data types represent various kinds of data such as text, numbers, symbols, arrays, etc. Since Ruby is a pure Object-Oriented Language, all data types are based on classes. Here are the primary data types in Ruby:

1. Numbers
2. Boolean
3. Strings
4. Hashes
5. Arrays
6. Symbols

1. Numbers: A number is generally defined as a sequence of digits, which may include a dot for decimal places. Ruby supports both integer and floating-point numbers. Depending on their size, numbers can be categorized into Fixnum and Bignum. However, in modern Ruby versions, they have been unified under the Integer class.

Example:

				
					# Ruby program to illustrate Numbers Data Type

# Float type
distance = 0.2

# Both integer and float type
time = 15.0 / 3600
speed = distance / time
puts "The average speed of the cyclist is #{speed} km/h"

Output:

				
					The average speed of the cyclist is 48.0 km/h

2. Boolean: The Boolean data type represents two values: true or false. This data type is used for simple true/false conditions.

Example:

				
					# Ruby program to illustrate Boolean Data Type

if false
  puts "This won't be printed!"
else
  puts "This is False!"
end

if nil
  puts "nil is True!"
else
  puts "nil is False!"
end

if 1
  puts "1 is True!"
else
  puts "1 is False!"
end

Output:

				
					This is False!
nil is False!
1 is True!

3. Strings: A string is a collection of characters enclosed within either single (') or double (") quotes. Double-quoted strings allow for string interpolation and special character sequences, while single-quoted strings only support limited escape sequences.

Example:

				
					# Ruby program to illustrate Strings Data Type

puts "Ruby String Data Type"
puts 'Escape using "\\"'
puts 'It\'s a beautiful day!'

Output:

				
					Ruby String Data Type
Escape using "\"
It's a beautiful day!

4. Hashes: A hash is a collection of key-value pairs, similar to a dictionary in Python or an associative array in PHP. Keys and values are separated by => and each pair is enclosed within curly braces {}.

Example:

				
					# Ruby program to illustrate Hashes Data Type

colors = { "red" => "#FF0000", "green" => "#00FF00", "blue" => "#0000FF" }
colors.each do |color, hex|
  puts "#{color} has hex value #{hex}"
end

Output:

				
					red has hex value #FF0000
green has hex value #00FF00
blue has hex value #0000FF

5. Arrays: An array is an ordered collection of elements, which can contain data of any type. Elements are separated by commas and enclosed within square brackets []. Arrays in Ruby can hold mixed data types.

Example

				
					# Ruby program to illustrate Arrays Data Type

data = ["Alice", 25, 5.5, "Hello, world!", "last item"]
data.each do |element|
  puts element
end

Output:

				
					Alice
25
5.5
Hello, world!
last item

6. Symbols: Symbols are lightweight, immutable strings. They are used instead of strings in situations where memory optimization is crucial. A symbol is prefixed with a colon (:).

Example:

				
					# Ruby program to illustrate Symbols Data Type

countries = { :us => "United States", :ca => "Canada", :fr => "France" }

puts countries[:us]
puts countries[:ca]
puts countries[:fr]

Output:

				
					United States
Canada
France

Types of Variables in Ruby

In Ruby, there are four main types of variables, each serving different purposes and having different scopes. Each type is distinguished by a special character at the beginning of the variable name.

Symbol	Type of Variable
`[a-z]` or `_`	Local Variable
`@`	Instance Variable
`@@`	Class Variable
`$`	Global Variable

1. Local Variables: Local variables in Ruby start with a lowercase letter (a-z) or an underscore (_). They are restricted to the scope in which they are defined (e.g., inside a method or a block). Local variables do not need to be initialized before use.

Example:

				
					# Ruby program to illustrate Local Variables

# Local variables
name = "Alice"
_age = 30

puts "Name: #{name}"
puts "Age: #{_age}"

Output:

				
					Name: Alice
Age: 30

2. Instance Variables: Instance variables start with an @ sign. They belong to a specific instance of a class and are accessible across different methods within that instance. Each instance of the class can have different values for its instance variables. Uninitialized instance variables have a nil value by default.

Example:

				
					# Ruby program to illustrate Instance Variables

class Book
  def initialize(title, author)
    # Instance variables
    @title = title
    @auth_name = author
  end

  def display_info
    puts "Title: #{@title}"
    puts "Author: #{@auth_name}"
  end
end

# Creating objects
book1 = Book.new("Ruby Programming", "John Doe")
book2 = Book.new("Learning Ruby", "Jane Doe")

# Calling methods
book1.display_info
book2.display_info

Output:

				
					Title: Ruby Programming
Author: John Doe
Title: Learning Ruby
Author: Jane Doe

3. Class Varia: Class variables start with @@ and are shared across all instances of a class. They belong to the class itself rather than any individual instance. Class variables must be initialized before they are used. An uninitialized class variable will raise an error.

Example:

				
					# Ruby program to illustrate Class Variables

class Library
  # Class variable
  @@book_count = 0

  def initialize(title)
    # Instance variable
    @title = title
  end

  def display_title
    puts "Book Title: #{@title}"
  end

  def add_book
    # Increment the class variable
    @@book_count += 1
    puts "Total books: #@@book_count"
  end
end

# Creating objects
book1 = Library.new("The Art of Ruby")
book2 = Library.new("Ruby on Rails Guide")

# Calling methods
book1.display_title
book1.add_book

book2.display_title
book2.add_book

Output:

				
					Book Title: The Art of Ruby
Total books: 1
Book Title: Ruby on Rails Guide
Total books: 2

4. Global Variables: Global variables start with a $ sign and are accessible from anywhere in the Ruby program. They are not limited to a specific class or scope. By default, an uninitialized global variable has a nil value. However, excessive use of global variables can make code difficult to debug and maintain.

Example:

				
					# Ruby program to illustrate Global Variables

# Global variable
$global_count = 5

class FirstClass
  def display_count
    puts "Global count in FirstClass: #$global_count"
  end
end

class SecondClass
  def display_count
    puts "Global count in SecondClass: #$global_count"
  end
end

# Creating objects
obj1 = FirstClass.new
obj2 = SecondClass.new

# Calling methods
obj1.display_count
obj2.display_count

Output:

				
					Global count in FirstClass: 5
Global count in SecondClass: 5

Global Variable in Ruby

Global variables have a global scope, meaning they are accessible from anywhere in a program. Modifying global variables from any point in the code has implications across the entire program. Global variables are always denoted with a dollar sign ($). If a variable needs to be shared across multiple classes, defining it as a global variable ensures it can be accessed from all classes. By default, an uninitialized global variable has a nil value, which can lead to confusing and complex code. Global variables can be modified from any part of the program.

Syntax:

				
					$global_variable = 5

Example:

				
					# Ruby program demonstrating global variables

# Defining a global variable
$global_variable = 20

# Defining first class
class FirstClass
  def display_global
    puts "Global variable in FirstClass is #$global_variable"
  end
end

# Defining second class
class SecondClass
  def display_global
    puts "Global variable in SecondClass is #$global_variable"
  end
end

# Creating instances of both classes
first_instance = FirstClass.new
first_instance.display_global

second_instance = SecondClass.new
second_instance.display_global

Output:

				
					Global variable in FirstClass is 20
Global variable in SecondClass is 20

In the above example, a global variable is defined with the value 20, and it can be accessed in both classes.

Another Example:

				
					# Ruby program to demonstrate global variables across methods and classes

$global_variable1 = "Hello"

class SampleClass
  def show_global_in_instance_method
    puts "Global variables are accessible here: #{$global_variable1}, #{$another_global_var}"
  end

  def self.set_global_in_class_method
    $another_global_var = "World"
    puts "Global variables are accessible here: #{$global_variable1}"
  end
end

# Using the class method
SampleClass.set_global_in_class_method

# Creating an object and using the instance method
sample_object = SampleClass.new
sample_object.show_global_in_instance_method

Output:

				
					Global variables are accessible here: Hello
Global variables are accessible here: Hello, World

Literal

In Ruby, a literal is any constant value that can be assigned to a variable. We use literals whenever we type an object directly into the code. Ruby literals are similar to those in other programming languages, with some differences in syntax and functionality.

Types of Ruby Literals

Ruby supports various types of literals:

1. Booleans and nil
2. Numbers
3. Strings
4. Symbols
5. Ranges
6. Arrays
7. Hashes
8. Regular Expressions

1. Booleans and nil: Booleans are constants that represent the truth values true and false. nil is another constant that represents an “unknown” or “empty” value, and it behaves similarly to false in conditional expressions.

Example:

				
					# Boolean literals demonstration
puts(5 + 2 == 7)  # true
puts(5 - 3 != 2)  # false
puts(nil == false)  # false

Output:

				
					true
false
false

2. Numbers: Ruby supports different types of numbers, including integers and floating-point numbers. You can write numbers of any size, using underscores (_) for readability. Ruby allows various numerical formats, including decimal, hexadecimal, octal, and binary.

Example:

				
					# Number literals demonstration
puts("Sum: ", 100 + 2_00 + 300)  # underscores for readability
puts("Hexadecimal:", 0x1A)  # hexadecimal
puts("Octal:", 0o56)  # octal
puts("Decimal:", 123)  # decimal
puts("Binary:", 0b1101)  # binary
puts("Float:", 1.234E2)  # scientific notation

Output:

				
					Sum: 600
Hexadecimal: 26
Octal: 46
Decimal: 123
Binary: 13
Float: 123.4

3. Strings: Strings in Ruby can be enclosed in either double quotes (" ") or single quotes (' '). Double-quoted strings support interpolation and special characters, while single-quoted strings only support limited escape sequences.

Example:

				
					# String literals demonstration
puts("The result of 3 + 4 is: #{3 + 4}")  # string interpolation
puts("Hello\nWorld")  # new line in double quotes
puts('Hello\nWorld')  # no new line in single quotes

Output:

				
					The result of 3 + 4 is: 7
Hello
World
Hello\nWorld

4. Symbols: A symbol in Ruby is a lightweight, immutable string used as an identifier. Symbols are created using a colon (:) and are never garbage-collected, making them memory-efficient for repeated use.

Example:

				
					# Symbol demonstration
puts(:user_id)  # simple symbol
puts(:"user#{42}")  # symbol with interpolation

Output:

				
					user_id
user42

5. Ranges: Ranges represent a set of values between a starting and an ending point. They can include numbers, characters, or other objects. Ranges can be constructed using the .. (inclusive) or ... (exclusive) operators.

Example:

				
					# Range literals demonstration
for i in 1..4 do
  puts(i)
end

puts("Exclusive range:", (1...4).to_a)

Output:

				
					1
2
3
4
Exclusive range: [1, 2, 3]

6. Arrays: An array is a collection of objects in Ruby, enclosed within square brackets ([ ]). Arrays can contain objects of different data types, and elements are separated by commas.

Example:

				
					# Array demonstration
fruits = ['apple', 'banana', 'cherry']
puts(fruits[0])  # accessing the first element
puts(fruits[1..2])  # accessing a range of elements
puts("Negative index:", fruits[-1])  # accessing the last element

Output:

				
					apple
banana
cherry
Negative index: cherry

7. Hashes: A hash is a collection of key-value pairs, similar to dictionaries in other languages. Hashes are defined using curly braces ({ }), and symbols can be used as keys for efficiency.

Example:

				
					# Hash demonstration
person = { name: "Alice", age: 30, city: "Wonderland" }

# Accessing hash elements
puts(person[:name])
puts(person[:age])

# Iterating over the hash
person.each do |key, value|
  puts("#{key} => #{value}")
end

Output:

				
					Alice
30
name => Alice
age => 30
city => Wonderland

8. Regular Expressions: Ruby supports regular expressions (regex) for pattern matching. Regular expressions are defined using forward slashes (/pattern/) or %r{pattern}.

Example:

				
					# Regular expression demonstration
line1 = "The quick brown fox"
line2 = "Jumps over the lazy dog"

# Checks if 'quick' is in line1
if (line1 =~ /quick/)
  puts line1
end

# Checks if 'lazy' is in line2 using %r{} format
if (line2 =~ %r{lazy})
  puts line2
end

# Checks if 'rabbit' is in line2
if (line2 =~ /rabbit/)
  puts line2
else
  puts "No match found"
end

Output:

				
					The quick brown fox
Jumps over the lazy dog
No match found

Ruby Directories

Working with Directories in Ruby

A directory is a location where files can be stored. In Ruby, the Dir class and the FileUtils module provide various methods for managing directories, while the File class handles file operations. Double dot (..) refers to the parent directory, and single dot (.) refers to the current directory itself.

The Dir Class

The Dir class allows access to and manipulation of directory structures in Ruby. It includes methods for listing directory contents, creating directories, changing directories, and more.

Features of the Dir Class

1. Creating Directories: The mkdir method is used to create a new directory. It returns 0 if the directory is successfully created.

Syntax:

				
					Dir.mkdir "directory_name"

Examples:

				
					# Creating a directory named "my_folder"
result = Dir.mkdir "my_folder"

# Output the result
puts result

Output:

2. Checking Directories: The exist? method checks if a directory exists.

Syntax:

				
					Dir.exist? "directory_name"

Example:

				
					# Create a directory named "my_folder"
Dir.mkdir("my_folder")

# Check if the directory exists
puts Dir.exist?("my_folder")

Output:

				
					true

The empty? method checks if a directory is empty.

Syntax:

				
					Dir.empty? "directory_name"

3. Working with Directories

The new method creates a new directory object (the directory should already exist).

Syntax:

				
					obj = Dir.new("directory_name")

The pwd method returns the current working directory.

Syntax:

				
					Dir.pwd

Example:

				
					# Create a directory named "example_folder"
Dir.mkdir("example_folder")

# Print the current working directory
puts Dir.pwd

Output:

				
					/path/to/current/directory

The home method returns the home directory of the current user.

Syntax:

				
					Dir.home

Example:

				
					# Print the home directory
puts Dir.home

Output:

				
					/Users/username

The path method returns the path of a directory object.

Syntax:

				
					d = Dir.new("directory_name")
d.path

Output:

Odd

Example:

				
					# Create a directory and get its path
Dir.mkdir("example_folder")
obj = Dir.new("example_folder")
puts obj.path

Output:

				
					example_folder

The getwd method returns the path of the current directory.

Syntax:

				
					Dir.getwd

Example:

				
					/path/to/current/directory

The chdir method changes the current working directory.

Syntax:

				
					Dir.chdir("directory_name")

Example:

				
					# Create directories
Dir.mkdir("/workspace/folder1")
Dir.mkdir("/workspace/folder2")

# Change to folder2
Dir.chdir("/workspace/folder2")
puts Dir.pwd

Output:

				
					/workspace/folder2

The entries method lists all files and folders in a directory.

Syntax:

				
					Dir.entries("directory")

Example:

				
					# Create a directory and subdirectories
Dir.mkdir("main_folder")
Dir.chdir("main_folder")
Dir.mkdir("subfolder1")
Dir.mkdir("subfolder2")

# List all files and folders
puts Dir.entries(".")

Output:

				
					.
..
subfolder1
subfolder2

The glob method lists files matching a certain pattern.

Syntax:

				
					Dir.glob("pattern")

Example:

				
					# Create files and folders
Dir.mkdir("sample_folder")
Dir.chdir("sample_folder")
Dir.mkdir("test")
Dir.mkdir("demo.rb")
Dir.mkdir("script.rb")

# List files matching patterns
puts Dir.glob("*.rb")

Output:

				
					demo.rb
script.rb

4. Removing Directories: Methods like rmdir, delete, and unlink are used to remove directories.

Syntax:

				
					Dir.delete "directory_name"
Dir.rmdir "directory_name"
Dir.unlink "directory_name"

Example:

				
					# Create a directory
Dir.mkdir("temp_folder")
puts Dir.exist?("temp_folder")

# Remove the directory
Dir.rmdir("temp_folder")
puts Dir.exist?("temp_folder")

Output:

				
					true
false

5. Creating Nested Directories: The mkdir_p method from the FileUtils module creates a directory and all its parent directories.

Syntax:

				
					FileUtils.mkdir_p 'directory_path'

Example:

				
					require "fileutils"

# Create nested directories
FileUtils.mkdir_p "parent/child/grandchild"

# Check existence
Dir.chdir("parent/child")
puts Dir.exist?("grandchild")

Output:

				
					true

6. Moving Files and Folders: The mv method from the FileUtils module is used to move files or directories.

Syntax:

				
					FileUtils.mv("source", "destination")

Example:

				
					require "fileutils"

# Create directories
Dir.mkdir "source_folder"
Dir.mkdir "destination_folder"

# Move source_folder into destination_folder
FileUtils.mv("source_folder", "destination_folder")

# Check if the move was successful
Dir.chdir("destination_folder")
puts Dir.exist?("source_folder")

Output:

				
					true

7. Copying Files: The cp method from the FileUtils module copies files from one location to another.

Syntax:

				
					FileUtils.cp("source", "destination")

Example:

				
					require "fileutils"

# Copy file.txt from source_folder to destination_folder
FileUtils.cp("source_folder/file.txt", "destination_folder")

# Check if the file exists in the destination
Dir.chdir("destination_folder")
puts File.exist?("file.txt")

Output:

				
					true

Contents

Basic Concepts

Ruby Keywords

Common Ruby Keywords

Ruby Data Types

Types of Variables in Ruby

Global Variable in Ruby

Literal

Ruby Directories

Working with Directories in Ruby

The Dir Class

Related Chapters

CATEGORY

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