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main_block.rb

This Ruby code snippet demonstrates a common pattern in Ruby programming: using the __FILE__ constant to check if the script is being run directly or included as a library. If the script is being run directly, the code block inside the if statement will be executed. This is useful for scripts that need to perform some action only when they are run directly, and not when they are required by another script.

For example, if you have a Ruby script called my_script.rb, you can use the following code to check if it’s being run directly or included as a library:

if __FILE__ == $0
  # Code block to be executed only if the script is run directly
end

If the script is run directly, the code inside the if statement will be executed. If the script is required by another script using the require method, the code inside the if statement will not be executed.

Note that the $0 constant is a special variable in Ruby that refers to the name of the current script being run. When a script is run directly, $0 will have the value of the script’s file name, and when it’s required by another script, $0 will have the value of the requiring script’s file name.

Ruby code snippet

if __FILE__ == $0
  # Code block to be executed only if the script is run directly

  # Add your script's main logic here
end
#=> nil

Executed with Ruby 3.4.4.