Why do we pass 0 as a parameter to "exit"?

Question

In the book learn ruby the hard way, I found a syntax to exit from the program:

Process.exit(0)

Why is the parameter 0 being passed in the exit method here even though it works if I pass another integer or do not pass any parameter? What is the significance of 0?

Answer 1

It is because when a child process is started (child process being your Ruby script in that case) the parent process (shell, system, etc.) can wait for it to finish.

Once it's finished, it can tell the parent process what is the status of it's execution. Zero usually means that the execution has been successfull and completed without any errors.

If you, on example, run your script from bash shell, and it will call Process.exit(0), you could check if it succeeded using $? variable:

$ ./my_ruby.script        # calls Process.exit(0)
$ echo $?
0                         # ok, script finished with no errors.

Answer 2

This is an 'exit code'.

This exit code has special meaning in some cases (see for example http://tldp.org/LDP/abs/html/exitcodes.html)

You can pass whatever you want, if the code isn't caught after, this will have no effects.

Here '0' is for 'Everything works fine !'