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Command history is a feature in many operating system shells, computer algebra programs, and other software that allows the user to recall, edit and rerun previous commands.
History was first introduced by Bill Joy in the C shell in 1978. It quickly became popular because it was fast and easy to use. History has since become a standard feature in other shells, including ksh, bash and Microsoft's cmd.exe, History addressed two major user scenarios:
- Executing the same command or short sequence of commands over and over. An example might be a developer frequently compiling and running a program.
- Correcting mistakes or rerunning a command with only a small modification of a previous one.
In Joy's original C shell, the user could refer to a previous command by typing an exclamation, !, followed by additional characters to specify a particular command, only certain words, or to edit it in some way before pasting it back into the command line. For example:
!!meant the entire previous command.!$meant just the last word of the previous command.!abc meant the command that started with abc.
The usual implementation today is to combine history with command line editing. The cursor keys are used to navigate up and down through the history list and left or right to anyplace on the line, where the user can simply type a desired change. But some implementations are menu based: The user presses a certain function key which displays a menu of recent commands, which the user can select one by typing a number.