Find File Space Usage

Find space used on filesystem level:
du -ks # shows summary of space used on disk in Kb
du -ms # shows summary of space used on disk in Mb
du -gs # show summary of space used on disk in Gb

Find space used on a file level:
find . -type f -ls | awk '{print $7}' | while read size
do
((TSIZE=TSIZE + $size))
done
echo "$TSIZE"

Shows largest files in a directory:
ls -l | sort -k 5rn,5 -k 9fd,9
-k = search criteria
5 = sort column five
r = apply reverse sort
n = numeric sort

Shows files using the most space on the filesystem:
du -ak | sort -k 1rn -k 2fd

Shows users using the most space:
# this space list will not include files or dirs that the current
# user has no read permissions on
ls /home/ | while read a
do
du -sm /home/$a
done 2> /dev/null | sort -k 1n | tail -10


http://www.devdaily.com/unix/edu/examples/sort.shtml
http://www.cs.rit.edu/~vcss231/Labs/Tips/unix-w8.html