This is an awesome trick I learnt recently. It’s a great trick if you don’t know how many times you need to run your macro. In short it is called a recursive macro :)

The gist is, you first make sure the register you are going to record your macro in is empty. Now while recording your macro call the register you are recording in as the last command.

For example if you are recording your macro in register a -

In command mode, first make sure your register is empty -

qaq

or

:let @a=""

You can confirm your register is empty by printing the contents of register a by using -

"ap

Now suppose I am working on a python script and need to comment out the script from current line to end of buffer, I would run this in command mode -

qaI#^[j@aq

Here is the breakdown
qa - start recording in register a
I# - Insert # in the beginning of current line
^[ - Thats what gets types when you hit escape to come out of insert mode
j - go down to next line
@a - nothing happens as register a is empty
q - quit recording

When you execute @a again as register a now is set it calls itself and repeats till end of buffer. A very cool trick indeed!!

Another way using the visual mode is by using the following command

VG:normal @a

The problem with the visual mode is that it only works when your macro is only editing on a single line. If you macro spans across lines, the visual mode trick will not work. I have to confess, I still need to fully understand how to use normal in vim commands.