Learning GNU Emacs, 3rd Edition

6.9 Executing Macros on a Region

A special command lets you execute a macro on each line in a region. How frequently do you encounter an email with text that you want to yank, but that is quoted several indentation levels? Of course, we can think of several ways to delete the indentation quickly, but a line-oriented macro is a quick approach too. You define the macro and execute it on a region by typing C-x C-k r (for apply-macro-to-region-lines). Remember that earlier we said that macros should set themselves up to repeat? This command is different because it expects to work on one line at a time. You don't want to set it up to repeat by moving to the next line; it does that automatically.

Table 6-5 shows a quick line-oriented macro that deletes indentation marks from text quoted in an email or newsgroup message.

Table 6-5. Macro for deleting indentation marks

Keystrokes	Action
F3	Start the macro definition.
C-a	Move to the beginning of the line.
M-f	Move forward one word.
M-b	Move to the beginning of this word.
C-Space	Set the mark.
C-a	Move to the beginning of the line.
C-w	Delete the extraneous indentation characters.
F4	End the macro definition.

Initial state:

Text indented at various levels (Mac OS X).

Mark the text as a region, move to the beginning of the region, then type: C-x C-k r

Indentation is deleted (Mac OS X).

6.10 Beyond Macros

Macros are an important tool for streamlining repetitive editing. They let you write your own commands for performing complex tasks without needing to know anything more than you already know: the basic Emacs commands for moving around and manipulating text. Even if you're an Emacs novice, you should be able to use macros with little difficulty.

However, Emacs is almost infinitely flexible, and macros cannot do everything. In many situations, there's no substitute for writing a Lisp function that does exactly what you want. If you know Lisp or would like to learn some, you can write your own Lisp functions to do more complex tasks than keyboard macros can handle. Chapter 11 covers the basics of writing Lisp functions.

Table 6-6 summarizes macro commands.

Table 6-6. Macro commands

Keystrokes	Command name	Action
C-x (	kmacro-start-macro	Start macro definition.
F3	kmacro-start-macro-or-insert-counter	Start macro definition. If pressed while defining a macro, insert a counter.
C-x )	kmacro-end-macro	End macro definition.
F4	kmacro-end-or-call-macro	End macro definition (if definition is in progress) or invoke last keyboard macro.
C-x e	kmacro-end-and-call-macro	Execute last keyboard macro defined. Can type e to repeat macro.
C-x C-k n	name-last-kbd-macro	Name the last macro you created (before saving it).
(none)	insert-kbd-macro	Insert the macro you named into a file.
(none)	macroname	Execute a named keyboard macro.
C-x q	kbd-macro-query	Insert a query in a macro definition.
C-u C-x q	(none)	Insert a recursive edit in a macro definition.
C-M-c	exit-recursive-edit	Exit a recursive edit.
C-x C-k b	kmacro-bind-to-key	Bind a macro to a key (C-x C-k 0-9 and A-Z are reserved for macro bindings). Lasts for current session only.
C-x C-k Space	kmacro-step-edit-macro	Edit a macro while stepping through it (in our opinion, the interface is overly complex).
C-x C-k l	kmacro-edit-lossage	Turn the last 100 keystrokes into a keyboard macro. If any mouse clicks are among the last 100 keystrokes, does not work.
C-x C-k e	edit-kbd-macro	Edit a keyboard macro by typing C-x e for the last keyboard macro defined, M-x for a named macro, C-h l for lossage, or keystrokes for a macro bound to a key.
C-x C-k Enter	kmacro-edit-macro	Edit the last keyboard macro.
C-x C-k C-e	kmacro-edit-macro-repeat	Edit the last keyboard macro again.
C-x C-k C-t	kmacro-swap-ring	Transpose last keyboard macro with previous keyboard macro.
C-x C-k C-d	kmacro-delete-ring-head	Delete last keyboard macro from the macro ring.
C-x C-k C-p	kmacro-cycle-ring-previous	Move to the previous macro in the macro ring.
C-x C-k C-n	kmacro-cycle-ring-next	Move to the next macro in the macro ring.
C-x C-k r	apply-macro-to-region-lines	Apply this macro to each line in a region.