Linux Command Line and Shell Scripting Bible, 5th Edition

Chapter 21Advanced sed

In This Chapter

• Looking at multiline commands
• Holding space
• Negating a command
• Changing the flow
• Replacing via a pattern
• Placing sed commands in scripts
• Creating sed utilities

Chapter 19, “Introducing sed and gawk,” showed you how to use the basics of the sed editor to manipulate text in data streams. The basic sed editor commands are capable of handling most of your everyday text-editing requirements. This chapter looks at the more advanced features that the sed editor has to offer. These are features that you might not use as often. But when you need them, it’s nice to know that they’re available as well as how to use them.

Looking at Multiline Commands

When using the basic sed editor commands, you may have noticed a limitation. All the sed editor commands perform functions on a single line of data. As the sed editor reads a data stream, it divides the data into lines based on the presence of newline characters. The sed editor handles the data lines one at a time, processing the defined script commands on the data line and then moving on to the next line and repeating the processing.

Sometimes, you need to perform actions on data that spans more than one line. This is especially true if you’re trying to find or replace a phrase.

For example, if you’re looking for the phrase Linux System Administrators Group in your data, it’s quite possible that the phrase’s words can be split onto two lines. If you processed the text using a normal sed editor ...