fixed shellcheck errors and warnings

[fbartels]

only warning left is the following:

In backup line 91:
        IFS=' ' read HASH DATE TIME HOST DIR <<< "$LAST"
                                    ^-- SC2034: HOST appears unused. Verify it or export it.
                                         ^-- SC2034: DIR appears unused. Verify it or export it.

seems it could be removed, but also did not want to mess with it in case the monitor check should still be expanded.

Signed-off-by: Felix Bartels [email protected]