sed & awk, 2nd Edition

Chapter 2. Understanding Basic Operations

If you are starting out to learn sed and awk, you can benefit from looking at how much they have in common.

• They are invoked using similar syntax.

• They are both stream-oriented, reading input from text files one line at a time and directing the result to standard output.

• They use regular expressions for pattern matching.

• They allow the user to specify instructions in a script.

One reason they have so much in common is that their origins can be found in the same line editor, ed. In this chapter, we begin by taking a brief look at ed and show how sed and awk were logical steps towards the creation of a programmable editor.

Where sed and awk differ is in the kind of instructions that control the work they do. Make no mistake—this is a major difference, and it affects the kinds of tasks that can best be performed with these programs.

This chapter looks at the command-line syntax of sed and awk and the basic structure of scripts. It also offers a tutorial, using a mailing list, that will give you a taste of script writing. It is valuable to see sed and awk scripts side-by-side before you concentrate on either one of them.