UNIX° TEXT PROCESSING

Let the Computer Do the Dirty Work

Computers are very good at doing the same thing repeatedly, or doing a series of very similar things one after another. These are just the kinds of things that people hate to do, so it makes sense to learn how to let the computer do the dirty work.

As we discussed in Chapter 7, you can save ex commands in a script, and execute the script from within vi with the :so command. It is also possible to apply such a script to a file from the outside—without opening the file with vi. As you can imagine, when you apply the same series of edits to many different files, you can work very quickly using a script.

In addition, there is a special UNIX editor, called sed (stream editor), that only works with scripts. Although sed can be used to edit files (and we will show many useful applications in this chapter), it has a unique place in the UNIX editing pantheon not as a file editor, but as a filter that performs editing operations on the fly, while data is passed from one program to another through a pipe.

The sed editor uses an editing syntax that is similar to that used by ex, so it should not be difficult to learn the basics.

The awk program, which is discussed in the next chapter, is yet another text-processing program. It is similar to sed, in that it works from the outside and can be used as a filter, but there the resemblance ends. It is really not ...