Using Macros in Vim
Jan 26 2021
For a long time, macros in Vim were a huge mystery for me. I knew they existed, but I didn't know how or why you'd use them. A recent task of mine involved replacing the unsafe operator (
!!) in a large kotlin codebase with a null-safe operator (
?). This game me a good opportunity to learn about macros. This is a snippet I encountered numerous times:
mLeftButton!!.text = "Left" mLeftButton!!.setOnClickListener(leftListener) mLeftButton!!.visibility = View.VISIBLE mRightButton!!.text = "Right" mRightButton!!.setOnClickListener(rightListener) mRightButton!!.visibility = View.VISIBLE
You could go ahead and change each line individually, or use the IDEs built in "multi-cursor" tool to save you some work. But, let me show you how I automated this using a Vim-Plugin for Android Studio. Not that the plugin matter, it will work in every Vim-like editor.
A macro in Vim works like this:
- Record any sequence of keystrokes and assign them to a key
- Execute that sequence as often as you wish
So let's see how we'd do that.
Recording a macro
To record a macro in Vim, you press
q (In normal mode) followed by a key you want to assign the macro to. So, if you wanted to record a macro and save it to the
q key, you'd press
q in normal mode again to quit your macro.
Coming back to my task, I would want to do the following:
_- Jump to the beginning of the line
f!- Find next occurrence of
cw- Change word (Delete word and enter insert mode)
?.- Insert the new characters
<esc>- Enter normal mode
j- go down a line
q- Finish macro
If everything went right, this line:
mLeftButton!!.text = "Left"
Should now look like this:
mLeftButton?.text = "Left"
and your macro should be saved under the
Using the macro
In order to use a macro in vim, you press the
@ key, followed by the key the macro is saved under. Since our macro is defined as
q, we'd press
@q, and the macro is executed immediately.
Let's take this further. You might have noticed that I went down a line before closing the macro. This becomes handy when you want to execute it many times. In our case we have 6 lines we want to refactor. 1 line has already been altered, so we have to execute it 5 more times. As per usual with vim, you can execute an action n times by specifying a number before doing the action. Let's press
5@q to execute the macro 5 times. And voila! Our unsafe code is now null-safe.
mLeftButton?.text = "Left" mLeftButton?.setOnClickListener(leftListener) mLeftButton?.visibility = View.VISIBLE mRightButton?.text = "Right" mRightButton?.setOnClickListener(rightListener) mRightButton?.visibility = View.VISIBLE
Macros are really satisfying to watch, if you ask me!
This is post 007 of #100DaysToOffload.