“Exit Traps” Can Make Your Bash Scripts Way More Robust and Reliable | Hacker News Reader

“Exit Traps” Can Make Your Bash Scripts Way More Robust and Reliable

redsymbol.net

23 pointskevinslin7 comments

This appears to be a duplicate of a recent post.

https://news.ycombinator.com/item?id=36400465

Very similar to Python's "finally" keyword [0] used in a try block, the "Exit Traps" are meant to allow for clean-up action(s) if a script fails.

[0]: https://docs.python.org/3/tutorial/errors.html#defining-clea...

How is finally() ever useful in any language? What is the difference between

  try{
      #code that can throw errors
  } catch {
    #handle error
  } finally {
    #code
  }

And

  try{
    #throw err
  }catch {
    #handle
  }
  #code...

Surely in pretty much all languages the two are equivalent, so what is finally's purpose as a token?

The trick in this post is different because for one bash doesn't have finally, and even if it did you couldn't use it to catch all of a script's errors.

`finally` will also cover scenarios where the an exception is raised from within catch, or if the catch block doesn't handle an exception that's raised in the `try` block.

If "handle error" in the catch involves rethrowing the error, or another error, or returning an error code from the function, the "finally" block is _still_ executed.

Here's a "fun" example in Javascript:

  function foo() {
    try {
      return 42
    } finally {
      return "boo!"
    }
  }

It is better to avoid bash scripts altogether :)

A POSIX shell occupies a special role in scripting. It embodies great power in a small space.

  $ ll /bin/dash /bin/bash
  -rwxr-xr-x. 1 root root 1388920 Jan 23 12:16 /bin/bash
  -rwxr-xr-x. 1 root root  128608 May  9 22:26 /bin/dash
  $ cat /etc/redhat-release 
  Red Hat Enterprise Linux release 9.2 (Plow)

Dash is the Debian/Ubuntu system shell, which supplanted bash sometime ago. You will not find comparable speed and power in that economy of size anywhere else.

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