Awk is a tool for processing text files, or data that is treated as text.
For some stuff I have been working on, I tend to use Awk a lot to filter down text being returned from another program (like a ls command).
Here is a nice tutorial on Awk.
Also, when using regular expressions (regexp, or regex) with Awk, here are a few helpful reminders and links.
|.||matches any character|
|*||zero or more repetitions of the previous character or expression|
|?||zero or one occurrence of the previous expression|
|+||one or more occurrences of the previous expression|
Regexp website (tutorials and more)