7.6. Command History
bash lets you display or modify previous commands. This is similar to the C shell's history mechanism. Commands in the history list can be modified using:
In addition, the command substitutions described in Chapter 8, "csh and tcsh", also work in bash.
7.6.1. Line-Edit Mode
Line-edit mode lets you emulate many features of the vi or Emacs editors. The history list is treated like a file. When the editor is invoked, you type editing keystrokes to move to the command line you want to execute. Arrow keys work on most terminals in both Emacs mode and vi command mode. You also can change the line before executing it. See Table 7-23 for some examples of common line-edit commands. When you're ready to issue the command, press Return.
The default line-edit mode is Emacs. To enable vi mode, enter:
$ set -o vi
Note that vi starts in input mode; to type a vi command, press Esc first.
The mode you use for editing bash commands is an entirely separate choice from the editor that is invoked for you automatically within many commands (for instance, the editor mail readers invoke when you ask them to create a new mail message). To change the default editor, set the VISUAL or EDITOR variable to the filename or full pathname of your favorite editor:
$ export EDITOR=emacs
Table 7-23. Common Editing Keystrokes
7.6.2. The fc Command
Use fc -l to list history commands and fc -e to edit them. See the entry under built-in commands for more information.
$ history List the last 16 commands $ fc -l 20 30 List commands 20 through 30 $ fc -l -5 List the last five commands $ fc -l cat List the last command beginning with cat $ fc -ln 5 > doit Save command 5 to file doit $ fc -e vi 5 20 Edit commands 5 through 20 using vi $ fc -e emacs Edit previous command using Emacs $ !! Reexecute previous command $ !cat Reexecute last cat command $ !cat foo-file Reexecute last command, adding foo-file to the end of the argument list
7.6.3. Command Substitution
7.6.4. Variables in Prompt
Using the following variables, you can display information about the current state of the shell or the system in your bash prompt. Set the PS1 variable to a string including the desired variables. For instance, the following command sets PS1 to a string that includes the \w variable in order to display the current working directory and the \! variable in order to display the number of the current command. The next line is the prompt displayed by the change.
$ PS1='\w: Command \!$ ' ~/book/linux: Command 504$
Some of the prompt variables are relatively new, such as \j and \l, so they may not be supported in your version of bash.
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