The script can be used as non-root and root.

As non-root, sh checkspace.sh shows the used space for your home directory only.

Used space in /home/johndoe:
74%
You must be root to check the whole disk.

As root, sudo sudo sh checkspace.sh shows the used space for the whole disk.

Used space on the disk:
72%
Everything is fine, keep going ^^

If the space used for the whole disk is above 90%, an interactive mode will ask if you want to empty the cache, and then it will ask for the /tmp folder.

Do you want to clean the cache now? Y/n
Y
Cleaning the cache
(...)
Do you want to remove files in the /tmp folder? Y/n
Y
Removing files in /tmp