Why does vim tell me that I added an autocommand?

Question

I have been changing "$OLD" to "~/new" in a lot of files lately, so I am now used to starting vim like this

$ vim file.txt

Enter

Lorem ipsum $OLD
Lorem .OLD ipsum

:%up (brings back %s:\$OLD:\~/new:gc)Enter

:wqEnter

$

So I added a new autocommand in ~/.vimrc, like this

if has("autocmd")
  au BufEnter %s:\$OLD:\~/new:gc
endif

and this

  au BufEnter :%s:\$OLD:\~/new:gc

And next time I tried vim, it wasn't as impressed as I was hoping:

$ vim file.txt

Enter

--- Auto-Commands ---
Press ENTER or type command to continue

Enter

Lorem ipsum $OLD
Lorem .OLD ipsum

:qEnter

$

Why is vim just telling me about the commands, instead of running them?

Answer 1

You didn't provide a pattern to au. Note the syntax:

:au[tocmd] [group] {event} {pat} [nested] {cmd}
                        Add {cmd} to the list of commands that Vim will
                        execute automatically on {event} for a file matching
                        {pat} autocmd-patterns.

:au[tocmd] [group] {event} {pat}
                        Show the autocommands associated with {event} and
                        {pat}.

The first adds an autocommand, and the second lists autocommands. That's why you got that output.

Answer 2

You should change:

au BufEnter %s:\$OLD:\~/new:gc

to:

au BufEnter * %s:\$OLD:\~/new:gc

or something else.