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20.5 Information from the Command Loop

The editor command loop sets several Lisp variables to keep status records for itself and for commands that are run. With the exception of this-command and last-command it’s generally a bad idea to change any of these variables in a Lisp program.

Variable: last-command

This variable records the name of the previous command executed by the command loop (the one before the current command). Normally the value is a symbol with a function definition, but this is not guaranteed.

The value is copied from this-command when a command returns to the command loop, except when the command has specified a prefix argument for the following command.

This variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.

Variable: real-last-command

This variable is set up by Emacs just like last-command, but never altered by Lisp programs.

Variable: last-repeatable-command

This variable stores the most recently executed command that was not part of an input event. This is the command repeat will try to repeat, See Repeating in The GNU Emacs Manual.

Variable: this-command

This variable records the name of the command now being executed by the editor command loop. Like last-command, it is normally a symbol with a function definition.

The command loop sets this variable just before running a command, and copies its value into last-command when the command finishes (unless the command specified a prefix argument for the following command).

Some commands set this variable during their execution, as a flag for whatever command runs next. In particular, the functions for killing text set this-command to kill-region so that any kill commands immediately following will know to append the killed text to the previous kill.

If you do not want a particular command to be recognized as the previous command in the case where it got an error, you must code that command to prevent this. One way is to set this-command to t at the beginning of the command, and set this-command back to its proper value at the end, like this:

(defun foo (args…)
  (interactive …)
  (let ((old-this-command this-command))
    (setq this-command t)
    …do the work…
    (setq this-command old-this-command)))

We do not bind this-command with let because that would restore the old value in case of error—a feature of let which in this case does precisely what we want to avoid.

Variable: this-original-command

This has the same value as this-command except when command remapping occurs (see Remapping Commands). In that case, this-command gives the command actually run (the result of remapping), and this-original-command gives the command that was specified to run but remapped into another command.

Function: this-command-keys

This function returns a string or vector containing the key sequence that invoked the present command, plus any previous commands that generated the prefix argument for this command. Any events read by the command using read-event without a timeout get tacked on to the end.

However, if the command has called read-key-sequence, it returns the last read key sequence. See Key Sequence Input. The value is a string if all events in the sequence were characters that fit in a string. See Input Events.

;; Now use C-u C-x C-e to evaluate that.
     ⇒ "^U^X^E"
Function: this-command-keys-vector

Like this-command-keys, except that it always returns the events in a vector, so you don’t need to deal with the complexities of storing input events in a string (see Strings of Events).

Function: clear-this-command-keys &optional keep-record

This function empties out the table of events for this-command-keys to return. Unless keep-record is non-nil, it also empties the records that the function recent-keys (see Recording Input) will subsequently return. This is useful after reading a password, to prevent the password from echoing inadvertently as part of the next command in certain cases.

Variable: last-nonmenu-event

This variable holds the last input event read as part of a key sequence, not counting events resulting from mouse menus.

One use of this variable is for telling x-popup-menu where to pop up a menu. It is also used internally by y-or-n-p (see Yes-or-No Queries).

Variable: last-command-event

This variable is set to the last input event that was read by the command loop as part of a command. The principal use of this variable is in self-insert-command, which uses it to decide which character to insert.

;; Now use C-u C-x C-e to evaluate that.
     ⇒ 5

The value is 5 because that is the ASCII code for C-e.

Variable: last-event-frame

This variable records which frame the last input event was directed to. Usually this is the frame that was selected when the event was generated, but if that frame has redirected input focus to another frame, the value is the frame to which the event was redirected. See Input Focus.

If the last event came from a keyboard macro, the value is macro.

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