find . -type f -mtime +90 -printf '%s\n' | awk '{total=total+$1}END{print total/1e+9}'
Gigabyte
find . -type f -mtime +90 -printf '%s\n' | awk '{total=total+$1}END{print total/1e+6}'
Megabyte
find . -name "*.tmp" -print0 | xargs -0 rm
find /srv/nextcloud/data/marko/ -type f -regextype egrep -regex '.*\.(pdf|odt)' -printf '%s\n' | awk '{total=total+$1}END{print total/1e+9}'