Linux in a Nutshell, Fifth Edition

Command-Line Syntax | 755

sed

This is the Title of the Book, eMatter Edition

Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

sed Operation

sed operates as follows:

• Each line of input is copied into a pattern space, an internal buffer where edit-

ing operations are performed.

• 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 and address tests are

applied to the current line in the pattern space, not the original input line.

• The original input file is unchanged because the editing commands modify an

in-memory copy of each original input line. The copy is sent to standard out-

put (but can be redirected to a file).

• sed also maintains the hold space, a separate buffer that can be used to save

data for later retrieval.

Command-Line Syntax

The syntax for invoking sed has two forms:

sed [-n] [-e] 'command' file(s)

sed [-n] -f scriptfile file(s)

The first form allows you to specify an editing command on the command line,

surrounded by single quotes. The second form allows you to specify a scriptfile,a

file containing sed commands. Both forms may be used together, and they may be

used multiple times. If no file(s) is specified, sed reads from standard input.

Standard Options

The following options ...