Chapter 12. The sed Editor

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).