Ruby - Define Global Exception Handling using at_exit

1. Introduction

In Ruby, unexpected exceptions can sometimes cause a program to terminate prematurely. To ensure that we can handle such unexpected terminations gracefully, Ruby provides the at_exit method. This method allows developers to define a block of code that will be executed when the program exits, regardless of whether it's a normal exit or due to an exception. In this article, we will discuss how to use at_exit for global exception handling.

The at_exit method is a part of the Kernel module in Ruby. It allows you to register a block of code that will be executed just before the Ruby interpreter exits. When combined with the $! global variable (which holds the last exception raised), at_exit can be used to handle exceptions at a global level.

2. Program Steps

1. Define the at_exit block at the beginning or top level of your program.

2. Within the at_exit block, check the $! variable to see if an exception occurred.

3. If an exception occurred, handle or log the exception accordingly.

4. Write the rest of the program code, which might raise an exception.

3. Code Program

# Defining the at_exit block for global exception handling
at_exit do
  if $!
    puts "Caught an exception: #{$!.message}"
    puts "Backtrace:"
    $!.backtrace.each { |line| puts line }
    puts "No exceptions were raised. Exiting normally."
# Sample code that will raise an exception
puts "Starting the program..."
raise "This is an unexpected error!"
puts "End of the program..."


Starting the program...
Caught an exception: This is an unexpected error!
/path/to/file.rb:14:in `main'
No exceptions were raised. Exiting normally.


1. at_exit: The block of code defined by the at_exit method will be executed just before the Ruby interpreter exits.

2. if $!: We check if the $! variable (which holds the last exception) is set to determine if an exception was raised.

3. puts "Caught an exception: #{$!.message}": If an exception was raised, we print its message.

4. $!.backtrace.each { |line| puts line }: We print the backtrace for the exception to provide context about where and why it occurred.

5. raise "This is an unexpected error!": In our sample code, we raise an exception to demonstrate the functionality of the at_exit block.

6. Even though an exception is raised and it's not rescued in the main program flow, our at_exit block still catches and handles it gracefully.

Using at_exit for global exception handling ensures that we can always catch and handle exceptions, providing a safety net for unforeseen errors and allowing for a more resilient application.