Please make it easier to debug a custom script

[TjrGithub]

I had an error in a custom script. (Moral: Don't source a script that contains "exit 0".)

What I expected to happen is some kind of error log to help narrow down the problem. Instead, I found nothing: I looked into the firewall logs, into any other Afwall error logs, into the Android-wide log service, I executed iptables -L and my script on the command line, I put "set +x" into the script and tried to find the output, ...: no hint what went wrong, and no hint where else to look.

I ended up bisecting the problem: while read NUM_OF_LINES ; do head -n /sdcard/ipup.sh >/data/local/ipup.sh ; echo "Now test Afwall with $NUM_OF_LINES lines of custom script." ; done

On top of that, Afwall wouldn't even apply any firewall rules after removing the firewall scripts. Even after a reboot, it had the firewall set to disabled, leaking sensitive data (#342).

Afwall version 3.4.0 Fdroid
(Paid) Afwall unlocker Key version 1.0.2
Magisk 20.4
Magisk manager 7.5.1
LineageOS-for-microg 16.0 as of 2020-03-31 for Beryllium (Xiaomi Poco F1)