[Help-bash] Find out trap ERR from within a function when errtrace is unset?

[Patrick Schleizer]

Hi!

TLDR:

If errtrace is not in use, and one is within a function, is it possible
from within the function to find out which trap ERR is set on global level?

(This is related to my previous thread "run at global level from a
function".)

Long:

I know there are some issues with reusability [1] of bash shell
functions, but I wanted to see how far I come. Works okay for now for me
except for a small glitch I am asking about here.

Here is the pseudo code for the main script:

----------

#!/bin/bash

trap 'echo "trap ERR 1 of main script" ERR'

## do some stuff

source /path/to/some-bash-lib

## do some other stuff

trap 'echo "trap ERR 2 of main script" ERR'

## do some other stuff

function_provided_by_some_bash_lib

## function_provided_by_some_bash_lib runs an init function,
## that sets up shell options (dotglob etc.) as required and a deinit
function that undo it if necessary
## (if not already previously set by the main script.)

## The idea is for function_provided_by_some_bash_lib to have its own
trap ERR while it's running and to restore the trap of main script in
the deinit function.

----------

The idea is to use separate trap ERR in /path/to/some-bash-lib than in
the main script. So /path/to/some-bash-lib should not mess up traps in
the main script.

The following example works, even though "set -o errtrace" is not set,
the existing trap can be set, because it is set outside a function, on
global level.

----------

#!/bin/bash

trap "echo traptest" ERR

trap_extract() {
   ## Thanks to Richard Hansen - http://stackoverflow.com/a/7287873/2605155
   printf '%s\n' "$3"
}

existing_trap="$(eval "trap_extract $(trap -p ERR)")"

----------

The next example doesn't work, because "set -o errtrace" is not set.
Therefore the function trap_store_existing did not inherit the trap,
hence "trap -p ERR" cannot detect it.

----------

#!/bin/bash

trap "echo traptest" ERR

trap_extract() {
   ## Thanks to Richard Hansen - http://stackoverflow.com/a/7287873/2605155
   printf '%s\n' "$3"
}

trap_store_existing() {
   existing_trap="$(eval "trap_extract $(trap -p ERR)")"
}

trap_store_existing

----------

Cheers,
Patrick

[1] http://mywiki.wooledge.org/BashWeaknesses