On Linux, if your log file is defined inside the script  the easiest way to deal with it is to use the exec command:

SNAPLOG=$LOGDIR/snapshot.log

exec >> $SNAPLOG

exec 2>&1

# From here everything will be written in the log file without needing to use the redirection command ( > / >> )

Hi,

instead of : path = "export HOME=/tmp && unset LD_LIBRARY_PATH && soffice"

you can use path = "export HOME= $(eval echo ~$(id -u -n)) && unset LD_LIBRARY_PATH && soffice". 
That way soffice will use the home directory of the cache user running the job. It could be usefull, specialy if you need to add or modify parameters into the registrymodifications.xcu file.