# Chapter 12. The sed Editor

#### Contents:

Conceptual Overview
Command-Line Syntax
Syntax of sed Commands
Group Summary of sed Commands
Alphabetical Summary of sed Commands

This chapter presents the following topics:

- Conceptual overview of sed

- Command-line syntax

- Syntax of sed commands

- Group summary of sed commands

- Alphabetical summary of sed commands

For more information, see the O'Reilly book sed & awk, 2d ed., by Dale Dougherty and Arnold Robbins.

## 12.1. Conceptual Overview

sed is a noninteractive, or stream-oriented, editor. It interprets a script and performs the actions in the script. sed is stream-oriented, because, as with many Unix programs, input flows through the program and is directed to standard output. For example, sort is stream-oriented; vi is not. sed's input typically comes from a file but can be directed from the keyboard. Output goes to the screen by default but can be captured in a file instead.

Typical uses of sed include:

- Editing one or more files automatically

- Simplifying repetitive edits to multiple files

- Writing conversion programs

sed operates as follows:

- Each line of input is copied into a pattern space.

- All editing commands in a sed script are applied in order to each line of input.

- Editing commands are applied to all lines (globally) unless line addressing restricts the lines affected.

- If a command changes the input, subsequent commands are applied to the changed line, not to the original input line.

- The original input file is unchanged, because the editing commands modify a copy of the original input line. The copy is sent to standard output (but can be redirected to a file).

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