Awk

It's usually a better idea to use one command instead of using a pipe to another command, where possible. A common mistake:

# grep root /etc/passwd | awk -F: '{print $7}'
/bin/bash

which can be easily done all in awk:

# awk -F: '/root/ {print $7}' /etc/passwd
/bin/bash

Say you wanted to find out how much resident memory xfce4 was using on your system, and it appears most xfce applications start with "xf":

$ ps auwx | awk '/xf/{print $5}'
15924
14668
11948
11764
12944
16264
1860

If you wanted to use awk to add the results together instead of doing it manually:

$ ps auwx | awk '/xf/{ tot += $5 } END { print tot }'
69108

N.B. This can be misleading in the case of programs that use large amounts of shared memory (like java).