I’ve never liked the fact that vim doesn’t allow users to define commands that start with a lowercase letter. Every time I create one I end up having to also make a cnoreabbrev that lets me use my lowercase version. This has the ugly side effect of having text transform as you type. It also will make the cursor jump around if you’re doing more than changing the case of things. For example:

cnoreabbrev ack ack<c-\>esubstitute(getcmdline(), '^ack\>', 'Ack!', '')<enter>

This allows me to type “:ack ” and have it automatically change to “:Ack! ” as soon as I press <space>. The text changes automatically and my cursor jumps to the right two spaces instead of just one. Obviously this is a small inconvenience but it is an annoying one for me.

I have come up with a bit of a hacky workaround for this that allows more transparency and I thought I’d share in case someone out there is as stubborn as me. The following function will run a substitution on the current command line:

function! CommandLineSubstitute()
    let cl = getcmdline()
    if exists('g:command_line_substitutes')
        for [k, v] in g:command_line_substitutes
            if match(cl, k) == 0
                let cl = substitute(cl, k, v, "")
                break
            endif
        endfor
    endif
    return cl
endfunction

This function reads search/replace pairs from a global variable you set in your .vimrc. That global variable looks something like this:

" note that line continuation is only possible without 'C' in 'cpoptions'
let g:command_line_substitutes = [
    \ ['^ack ', 'Ack! '],
    \ ['^ee \(.\+\)', 'e **/\1*'],
    \ ['^h ', 'vertical help '],
\]

The last thing we need to do is a single map to call this function whenever we press <enter> on the command line:

cnoremap <enter> <c-\>eCommandLineSubstitute()<enter><enter>

While this configuration is a bit ugly, it saves me the inconvenience of having a bunch of abbreviations lying around and makes the substitution transparent to me.

I’ve only been using this for a few hours but I haven’t hit any issues thus far. If you try this out and have problems or if you know of a way to simplify it please let me know in the comments.