Bash-Beginners-Guide

Chapter 5. The GNU sed stream editor
At the end of this chapter you will know about the following topics:
♦ What is sed?
♦ Interactive use of sed
♦ Regular expressions and stream editing
♦ Using sed commands in scripts
This is an introduction
These explanations are far from complete and certainly not meant to be used as the
definite user manual for sed. This chapter is only included in order to show some more
interesting topics in the next chapters, and because every power user should have a basic
knowledge of things that can be done with this editor.
For detailed information, refer to the sed info and man pages.
5.1. Introduction
5.1.1. What is sed?
A Stream EDitor is used to perform basic transformations on text read from a file or a pipe. The result is sent
to standard output. The syntax for the sed command has no output file specification, but results can be saved
to a file using output redirection. The editor does not modify the original input.
What distinguishes sed from other editors, such as vi and ed, is its ability to filter text that it gets from a
pipeline feed. You do not need to interact with the editor while it is running; that is why sed is sometimes
called a batch editor. This feature allows use of editing commands in scripts, greatly easing repetitive editing
tasks. When facing replacement of text in a large number of files, sed is a great help.
5.1.2. sed commands
The sed program can perform text pattern substitutions and deletions using regular expressions, like the ones
used with the grep command; see Section 4.2.
The editing commands are similar to the ones used in the vi editor:
Table 5-1. Sed editing commands
Command Result
a\ Append text below current line.
c\ Change text in the current line with new text.
d Delete text.
i\ Insert text above current line.
Chapter 5. The GNU sed stream editor 62