5.1. What Is sed ?

Sed is a streamlined, noninteractive editor. It allows you to perform the same kind of editing tasks used in the vi and ex editors. Instead of working interactively with the editor, the sed program lets you type your editing commands at the command line, name the file, and then see the output of the editing command on the screen. The sed editor is nondestructive. It does not change your file unless you save the output with shell redirection. All lines are printed to the screen by default.

The sed editor is useful in shell scripts, where using interactive editors such as vi or ex would require the user of the script to have familiarity with the editor and would expose the user to making unwanted modifications to the open file. You can also put sed commands in a file called a sed script, if you need to perform multiple edits or do not like worrying about quoting the sed commands at the shell command line.^[1]

^[1] Remember, the shell will try to evaluate any metacharacters or whitespace when a command is typed at the command line; any characters in the sed command that could be interpreted by the shell must be quoted.