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Linux in a Nutshell

Chapter 12. The sed Editor

Contents:

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

sed is a noninteractive (stream-oriented) editor that interprets and performs the actions in a script. sed is said to be 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).

For more information on sed, see sed & awk (O'Reilly).

12.1. Command-Line Syntax

The syntax for invoking sed has two forms:

sed [options] 'command' file(s)
sed [options] -f scriptfile file(s)

The first form allows you to specify an editing command, surrounded by single quotes, on the command line. The second form allows you to specify a scriptfile, which is a file containing sed commands. If no files are specified, sed reads from standard input.

The following options are recognized:

-e cmd, --expression=cmd: Next argument is an editing command; not needed unless specifying two or more editing commands.
-f scriptfile, --file=scriptfile: Next argument is a file containing editing commands.
-n, --silent, --quiet: Suppress the default output; sed displays only those lines specified with the p command or with the p flag of the s command.
-V, --version: Display version number.
-h, --help: Display brief help message with command-line options.

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