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

23 points by kevinslin 3y ago

chasil 3y ago
This appears to be a duplicate of a recent post. https://news.ycombinator.com/item?id=36400465 https://news.ycombinator.com/item?id=36400465
noahjk 3y ago
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-clean-up-actions https://docs.python.org/3/tutorial/errors.html#defining-clea...
- themoonisachees 3y ago
  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.
  - anuragsoni 3y ago
    `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.
  - maskros 3y ago
    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!" } }
Rucadi 3y ago
It is better to avoid bash scripts altogether :)
- chasil 3y ago
  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.

23 points by kevinslin 3y ago

This appears to be a duplicate of a recent post. https://news.ycombinator.com/item?id=36400465 https://news.ycombinator.com/item?id=36400465

noahjk 3y ago

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-clean-up-actions https://docs.python.org/3/tutorial/errors.html#defining-clea...

themoonisachees 3y ago
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.
- anuragsoni 3y ago
  `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.
- maskros 3y ago
  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!" } }

Rucadi 3y ago

It is better to avoid bash scripts altogether :)

chasil 3y ago
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.