11.2 History in a Nutshell

The C shell and bash can save copies of the previous command lines you type. Later, you can ask for a copy of some or all of a previous command line. That can save time and retyping.

This feature is called history substitution , and it's done when you type a string that starts with an exclamation point ( ! command ). You can think of it like variable substitution ( $ varname ) ( 6.8 ) or command substitution ( ` command ` ) ( 9.16 ) : the shell replaces what you type (like !$ ) with something else (in this case, part or all of a previous command line).

Article 11.1 is an introduction to shell history. These articles show lots of ways to use history substitution:

• We start with favorite uses from several contributors - articles 11.3 , 11.4 , 11.5 , 11.6 .

• Article 11.7 starts with a quick introduction, then covers the full range of history substitutions with a series of examples that show the different kinds of things you can do with history.

  (Back in article 9.6 are examples of csh and bash operators like :r . Many of these can be used to edit history substitutions.)

• See an easy way to repeat a set of csh or bash commands in article 11.8 .

• Each shell saves its own history. To pass a shell's history to another shell, see articles 11.11 and 11.12 .

• You don't have to use an exclamation point ( ! ) for history. Article 11.15 shows how to use some other character.

• The Korn shell does history in a different way. Article 11.13 introduces part of that: command-line editing in ksh and bash .

One last note: putting the history number in your prompt ( 7.2 ) makes it easy to re-use commands that haven't scrolled off your screen.