How to trap exit code in Bash script

问题:

There're many exit points in my bash code. I need to do some clean up work on exit, so I used trap to add a callback for exit like this:

trap "mycleanup" EXIT

The problem is there're different exit codes, I need to do corresponding cleanup works. Can I get exit code in mycleanup?

回答1:

I think you can use $? to get the exit code.

回答2:

The accepted answer is basically correct, I just want to clarify things.

The following example works well:

#!/bin/bash

cleanup() {
    rv=$?
    rm -rf "$tmpdir"
    exit $rv
}

tmpdir="$(mktemp)"
trap "cleanup" INT TERM EXIT
# Do things...

But you have to be more careful if doing cleanup inline, without a function. For example this won't work:

trap "rv=$?; rm -rf $tmpdir; exit $rv" INT TERM EXIT

Instead you have to escape the $rv and $? variables:

trap "rv=\$?; rm -rf $tmpdir; exit \$rv" INT TERM EXIT

You might also want to escape $tmpdir, as it will get evaluated when the trap line gets executed and if the tmpdir value changes later that will not give you the expected behaviour.

Edit: Use shellcheck to check your bash scripts and be aware of problems like this.

回答3:

I've found it is better to separate EXIT trap from the trap for other signals

Example trap test script...

umask 77
tmpfile=`tmpfile.$$`
trap 'rm -f "$tmpfile"' EXIT
trap 'exit 2' HUP INT QUIT TERM

touch $tmpfile
read -r input 

exit 10

The temporary file is cleaned up. The file exit value of 10 is preserved! Interrupts result in an exit value of 2

Basically as long as you don't use "exit" in a EXIT trap, it will exit with the original exit value preserved.

ASIDE: Note the quoting in the EXIT trap. That lets me change what file needs to be cleaned up during the scripts lifetime. I often also include a test for the $tmpfile varables existence, so I don't even need to set it at the start of the script.