How to create an alias for a command in Vim?

Question

Vim is my preferred text editor when I program, and thus I always run into a particularly annoying issue.

Frequently, when I quickly need to save the buffer and continue on to some other miscellaneous task, I do the typical

:w

However, I always?— what seems to be like more than 50% of the time?— manage to capitalize that?:w. Naturally, Vim yells at me because W is an invalid command:

E492: Not an editor command: W

My question is how can one alias colon-commands in Vim. Particularly, could you exemplify how to alias W to w.

I am aware of the process to map keys to certain commands, but that is not what I’m looking for.

Answer 1

To leave completion untouched, try using

cnoreabbrev W w

It will replace?W in command line with?w, but only if it is neither followed nor preceded by word character, so :W<CR> will be replaced with :w<CR>, but :Write won’t. (Note that this affects any commands that match, including ones that you might not expect. For example, the command :saveas W Z will be replaced by :saveas w Z, so be careful with this.)

Update

Here is how I would write it now:

cnoreabbrev <expr> W ((getcmdtype() is# ':' && getcmdline() is# 'W')?('w'):('W'))

As a function:

fun! SetupCommandAlias(from, to)
  exec 'cnoreabbrev <expr> '.a:from
         .' ((getcmdtype() is# ":" && getcmdline() is# "'.a:from.'")'
         .'? ("'.a:to.'") : ("'.a:from.'"))'
endfun
call SetupCommandAlias("W","w")

This checks that the command type is?: and the command is?W, so it’s safer than just cnoreabbrev W w.