The Korn shell stores the commands that you enter at your terminal in a file, called the command history file. This file is specified by the HISTFILE variable. If not set, the default is $HOME/.sh_history.
The number of commands accessible via the command history file is specified by the HISTSIZE variable. If not set, the last 128 commands are saved, starting from your most recent command. The command history file operates on a first-in, last-out basis, so that as new commands are entered, the oldest commands are not accessible.
There are two ways to access the command history file: using the fc command, or the in-line editor. These are discussed in the following sections.