BEGIN and END in Ruby

BEGIN and END in Ruby

• Ruby's reserved terms BEGIN and END(in uppercase) designate code to be executed at the start and end of a Ruby program, respectively. 
   
• In Begin, the statement executes the code of that specific block at the very beginning. In contrast, the execution of code and the ‘End’ statement runs some specific code at the last moment of performance.
   
• Every Ruby source file can run both the BEGIN blocks when the file is loaded and the END blocks when the program is complete.
   
• Multiple BEGIN and END blocks are possible in a program, and the  END command is carried out at last.
   
• Always provide an open curly brace’{’ after the BEGIN and END keywords. There are also some differences between the BEGIN and END statements. We will be exploring them all further(Note that the words BEGIN and END in capital letters differ significantly from those in lowercase if there are many).
   
• They are executed in the sequence and the interpreter specifies in a program's BEGIN declaration confronts them. 
   
• If there are several END statements, they are all carried out in the first one instead of the sequence in which they are encountered.

Syntax

BEGIN and END must be followed by an open curly brace, Ruby code, and a close curly brace. Curly braces are required. Let's see with an example:

BEGIN
{
	# Your code for executing in beginning
	# Also used for Global initialization
}

END
{
	# Your code to be executed at the end
	# Also used for Global shutdown
}

You can also try this code with Online Ruby Compiler

Run Code

So let's grasp this with the help of an example:

Code 

# Ruby Program to demonstrate BEGIN and END Block
BEGIN { 
   # BEGIN block code is here
   puts "This is the Beginning."
} 
  
END { 
   # END block code is here
   puts "This is the end."
}
 
# MAIN block code 
puts "Welcome to Code studio."

You can also try this code with Online Ruby Compiler

Run Code

In this piece of code, the first statement will execute first, because it is a BEGIN statement, then all the other code will get executed, and the end block will get executed at the end. We can see the same in the output below.

Output

Difference between BEGIN and END

Following is the comparison between BEGIN and END in Ruby:

Code for Multiple BEGIN

As you can see, regardless of its position in the code or Ruby's regular top-down execution sequence, the BEGIN block executes at the beginning.

Multiple BEGIN blocks can also be used to separate sections of code. These blocks execute in the order they are defined in the code, meaning blocks defined earlier (higher up) in the source file execute first. Here's a simple example:

BEGIN {
	puts "Hello"
	# This will be printed
}

BEGIN {
	puts "Ninjas"
	# Also, this will be printed
}

BEGIN {
	puts "Welcome to Code Studio" 
	# This will also be printed
}

You can also try this code with Online Ruby Compiler

Run Code

As you can see in this code, regardless of the context in which it appears, the code associated with each of the three BEGIN statements will only run once. There won't be any defined variables outside of BEGIN blocks, and those that have been defined inside the block won't be visible outside.

Output

In the case of multiple end statements, the end statement written in the last will get executed first, as you can see in the below code:

Code for Multiple END

It is important to keep in mind that when utilizing multiple END blocks, they execute in the reverse order of their specification, meaning that the END blocks defined later (at the end of) the code run earlier. Here's a brief example:

END {
	puts "Hello" 	# This will be printed
}

END {
	puts "Ninja" 	# Also, this will be printed
} 

You can also try this code with Online Ruby Compiler

Run Code

In this code, there is two end statement, but we can see it is printing in LIFO order.

Output

Frequently Asked Questions

When to use BEGIN and END in Ruby?

Ruby's reserved keywords for the BEGIN and END blocks (both capitalized) are simple to employ. No matter where in the source file they are located, you can define certain code blocks to run at the start and end of your program's execution.

What is begin rescue in Ruby?

There is a likely exception in the code between "begin" and "rescue". The rescue block will go into action if an exception occurs.

What programming language uses begin to end?

Ruby's reserved terms BEGIN and END designate code to be executed at the start and end of a Ruby program, respectively.

Why do we use blocks in BEGIN and END in Ruby?

Ruby has closure-like structures called blocks, and they're central to the language. They can lessen repetition and possibly make coding less prone to errors when used appropriately.

What is binding in Ruby, and how is it used in the scope of BEGIN and END?

Ruby uses bindings, which capture the execution context at each location in the code to maintain track of the current scope. A Binding object that details the bindings at the current place is returned by the binding method.

Conclusion

In this blog, we have learned about statement and control Structure, specifically, BEGIN and END in Ruby, including Multiple BEGIN and END examples.

You can look at the following link to know Ruby in depth.

• Ruby
• Ruby: Code studio
• Documentation
• Official Ruby FAQ
• Ruby Koans
   

Read other related articles on Ruby:

• Boolean in Ruby
• Symbols in Ruby
• Defining A Simple Class In Ruby
• Variables in Ruby
• Ruby is an object-oriented language
   

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