Size of folder tree	du -h .| sort -nr
Size of current folder (level 1)	du -d 1| sort -nr
Quotas	quota -v

Delete files and folders in current folder older than 90 days#

find . -type d -mtime +90 -exec rm -rf {} \; 

Size of Folder#

Print current folder in kb (includes org space? it is not the sum of ls)

du -sk .

ls -l | awk '{t+=$5}END{print t}'
ls -lR . | awk '{sum += $5} END{print sum}'

exactly the sum of ls in MB

ls -lR . | awk '{sum += $5} END{printf "%2f\n", sum/1024/1024}'

ls -al | sort -nbk5 => sort by file size
ls -lrt => sort by date/time

Get sizes of folders and subfolders

du -h --max-depth=3

or a shell script:
#/bin/sh
du -k --max-depth=1 | sort -nr | awk '
     BEGIN {
        split("KB,MB,GB,TB", Units, ",");
     }
     {
        u = 1;
        while ($1 >= 1024) {
           $1 = $1 / 1024;
           u += 1
        }
        $1 = sprintf("%.1f %s", $1, Units[u]);
        print $0;
     }
    '

Get all files on specific dates#

find . -mtime -60                       (last 60 days)
find . -maxdepth 1 -mtime -1 -ls        (last 1 day)
find . -maxdepth 1 -mtime -0.007 -ls    (last 10 minutes)

Get all files for a date range and copy/move those#

find -type f -newermt 20141101 \! -newermt 20141218
mv -t <destination> `find -type f -newermt 20141101 \! -newermt 20141218`

Sort by time

ls -t
ls -tr

Pipes, see here

Append >>	cat $DATEIM >> $DATEIJ
Targeting >	cat $DATEIM > $DATEIJ