Is it possible to use "set -e" but allow certain commands to fail?

Question

I am working on a backup script and would like to stop the script on error except for certain commands such as veracrypt --mount which returns 1 when already mounted.

#! /bin/sh

set -e

veracrypt --text --mount --pim 0 --keyfiles "" --protect-hidden no "/Volumes/Samsung BAR/.b" /Volumes/Backup

borg check /Volumes/Backup/Borg

veracrypt --text --dismount "$BACKUP_VOLUME_PATH"

Answer 1

You can use || to execute something that won't fail if a primary command fails, such as with:

blah || true
{ yada; yada; yada; } || true

Without the || true, the script will complain on error then stop. With it, you'll still see the error but the script will carry on.

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Another possibility is taking advantage of the fact that it's not considered a failure if it's part of an if:

if blah ; then true ; fi

Even if blah errors, the script will carry on.

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Finally, you can turn it off temporarily for a specific command:

set +e ; blah ; set -e

This solution is only really workable if you already know the current setting. You probably don't want to turn on -e unless it was set before you turned it off.

To detect its current setting and only turn it back on if it was already on beforehand, you can use:

# 1: State here can be either +e or -e. If -e, record that fact and make +e.

eWasSet=false; [[ $- = *e* ]] && eWasSet=true && set +e

# 2: Do stuff that needs +e.

blah blah blah

# 3: Revert state if needed. After this, it's as it was in comment 1 above.

${eWasSet} && set -e

This works because $- contains all of the current set values (like ehB for error exit, hashing, and brace expansion), so you can use the wildcard equality operators to find out if a particular setting (like e) is active.