Chapter 6. Advanced sed Commands
In this chapter, we cover the remaining sed commands. These commands require more determination to master and are more difficult to learn from the standard documentation than any of the basic commands. You can consider yourself a true sed-master once you understand the commands presented here.
The advanced commands fall into three groupings:
Working with a multiline pattern space (N,D,P).
Using the hold space to preserve the contents of the pattern space and make it available for subsequent commands (H,h,G,g,x).
Writing scripts that use branching and conditional instructions to change the flow of control (:,b,t).
If the advanced scripts in this chapter have one thing in common, it is that they alter the sequential flow of execution or control. Normally, a line is read into the pattern space and each command in the script, one right after the other, is applied to that line. When the bottom of the script is reached, the line is output and the pattern space is cleared. Then a new line is read into the pattern space and control passes back to the top of the script. That is the normal flow of control in a sed script.
The scripts in this chapter interrupt or break the normal flow of control for various reasons. They might want to prevent commands in the script from executing except under certain circumstances, or to prevent the contents of the pattern space from being cleared out. Altering the flow of control makes a script much more difficult to read and ...
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