Command history is a common feature in command line interfaces in operating system shells (such as Korn shell, Bash, cmd.exe, etc.), computer algebra programs, and other software that interacts with the user through a command line. Command history involves making previously-entered commands, usually up to some limit, easy to once again input to the command line. The usual method is for the user to use the Up (and Down) keyboard keys to navigate through the command history, but some programs also offer the facility for the user to press a certain function key which will show a menu of recent commands, from which the user can select one by typing a number.