The awk command

The awk command is a pattern mathing utility that leverages regex. It is commonly used in *nix systems to reformat the output from one command and pass it to another command. For instance, take the following on my CentOS server:

cat /etc/redhat-release | awk '{print $3}'  

This command will take the normal output of:
      CentOS release 6.4 (Final)
and instead output:
       6.4

In *nix systems when you are recieving data from like a read or a redirection the arguments get represented as the numberings that they correspond with with a dollar sign prepended to them. In this case the third word was 6.4.

Take the date command as another example:

date #Sat Nov  2 00:13:50 EDT 2013  
#but
date | awk '{print $2 " " $3}' #Nov 2  

Pretty useful.

More resources

Awk By Example