Vim autocommand creates weird file

Question

I've just set up slackware 14 on a virtualbox. As one does, I immediatly created/altered my .bashrc and, more importantly, my .vimrc files.

To avoid writing huge lines of code, I usually add something like

au BufWinEnter * w:m1=matchadd('ErrorMsg','\%>100v.\+', -1)
if version >= 702
    au BufWinLeave * call clearmatches()
endif

I've used these settings for quite a while now, only this time, whenever I open a file in vim, a weird file is being created, with :m1=matchadd('ErrorMsg','\%>100v.\+', -1) as its name.
I've reduced my .vimrc file to just the basics, which I believe can't have anything to do with this oddity (vim-7.3.645-x86_64-1):

set nocompatible
set ai
set nu
set ruler
set hlsearch
set hidden
set showcmd
set cursorline
set confirm
syntax on
color evening
au BufWinEnter * w:m1=matchadd('ErrorMsg','\%>100v.\+', -1)
if version >= 702
    au BufWinLeave * call clearmatches()
endif

Any ideas what is causing this behaviour, and how to fix it?

Answer 1

That is expected; the autocmd executes the Ex command w:m1=matchadd('ErrorMsg','\%>100v.\+', -1). w is the short form of write, what follows is interpreted as the file name.

I guess a :let went missing, because then the command makes sense: let w:m1=... defines a window-local variable m1 and assigns the result of the matchadd() call to it.

---

The autocmd appears to highlight all characters beyond column 100. Note that in recent Vim 7.3 versions, you can use the 'colorcolumn' feature for that:

:set colorcolumn=101

Answer 2

If you add,

set vbs=1 " Verbose error reporting Zero = Norm to Nine = Max

into your .vimrc and start with a 3 or 4 it will show you all the files loaded/called (and a lot more as you push to 9) as you are opening vim/files.

Not an exact answer, but could help you track it down.