Unix in a Nutshell, 4th Edition

Command History

Previously executed commands are stored in a history list. You can access this list to verify commands, repeat them, or execute modified versions of them. The history built-in command displays the history list; the predefined variables histchars, history, and savehist also affect the history mechanism. There are a number of ways to use the history list:

• Rerun a previous command

• Edit a previous command

• Make command substitutions

• Make argument substitutions (replace specific words in a command)

• Extract or replace parts of a command or word

The easiest way to take advantage of the command history is to use the arrow keys to move around in the history, select the command you want, and then rerun it or use the editing features described in the section "Command-Line Editing,” later in this chapter, to modify the command. The arrow keys are:

Key	Description
Up arrow (↑)	Previous command.
Down arrow (↓)	Next command.
Left arrow (←)	Move left in command line.
Right arrow (→)	Move right in command line.

The next sections describe some tools for editing and rerunning commands. With the C shell, which does not have the command-line editing features of tcsh , these features are important for rerunning commands. With tcsh, they are less often used, but they still work.