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 (
You can think of it like
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:
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
are examples of csh and bash operators like
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.
You don't have to use an exclamation point (
!) for history.
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:makes it easy to re-use commands that haven't scrolled off your screen.