Awk

Awk and /etc/passwd

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

Awk and ps

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).

Awk and multi-row documents

pretend you have a file that has IP numbers where multiple can be on one row and you need to flatten these into 1 per row here is how the solution looks like:

francisco$ cat ipfile
192.168.0.1
192.168.0.2 192.168.0.3
10.0.0.1 10.0.0.2 10.0.0.3

francisco$ awk '{ for (i = 1; i <= NF ; i++) print $i; }' ipfile
192.168.0.1
192.168.0.2
192.168.0.3
10.0.0.1
10.0.0.2
10.0.0.3