Just learnt how to set and use Keyboard Macros in emacs. This looks pretty useful and something I feel will come in handy while refactoring code.

Firstly, to set a keyboard macros means recording a sequence of actions (keystrokes) and saving them. Later you can ask emacs to just repeat them for you whenever you want using a single command.

Setting macros is quite simple,

C-X ( ......begin a macro definition

...<do some keystrokes that you want to record>...

C-X ) ......end the macro definition

Now to "play" your recording anywhere, all you need to do is C-X e

Lets imagine a screnario:

In a php class (say a controller in an MVC application) the following expression is written a number of times to get a particular request param and assign it to a variable

<?php
$id = $this->request->param('id') .............. $user_id = $this->request->param('user_id');    

Suppose I want to pass a second optional parameter of value 0 to all of the function calls ie change them such as,

<?php
$this->request->param('id', 0);

To do this using a macro,

move to the beginning of the buffer by typing M-S-<.

Begin the macro definition C-X (

Incremental search for $this->request->param using C-s and then RET

end of line C-e

backward twice C-b * 2

type , 0

end macro definition C-X )

Now keep doing C-X e till all the method calls are modified.

(This was somewhat a vague example but I hope you get the idea :-))