Directory shortcuts in emacs buffer

Question

So I asked this question about directory shortcuts in a shell. The idea is I'd like to be able to open a file in /home/Documents/foo, say, by typing (C-x C-f) ~foo/file.

So, is there a way to emulate zsh's "named directories" in the emacs buffer? (Incidentally, the shortcut definitions I want to use are already in my .zshrc, if there's a solution that reads them directly, that gets bonus points...)

Answer 1

The Emacs component that's responsible for expanding ~ in file names is expand-file-name. Unfortunately, it's written in C, and deep inside its bowels is code that assumes that what comes after ~ is a user name. Fortunately, Emacs has a generic way of adding a wrapper around functions, so you can do what you want if you don't mind repeating some of the logic in the built-in function.

Here's some completely untested code that should get you going. Look up “Advising Emacs Lisp Functions” in the Emacs Lisp manual for more information; the basic idea is that defadvice adds some code to run before the actual code of expand-file-name. Please signal the mistakes I've inevitably made in comments (whether you know how to fix them or not).

(ad-define-subr-args 'expand-file-name '(name &optional default-directory))
(defvar expand-file-name-custom-tilde-alist
  '("foo" . "/home/Documents/foo"))
(defadvice expand-file-name (before expand-file-name-custom-tilde
                             activate compile)
  "User-defined expansions for ~NAME in file names."
  (save-match-data
    (if (string-match "\\`\\(\\(.*/\\)?~\\([^:/]+\\)\\)/" name)
        (let ((replacement (assoc (match-string 2 name) expand-file-name )))
          (if replacement
              (setq name (replace-match replacement t t name 1)))))))

I'll leave parsing the shortcuts in .zshrc to fill expand-file-name-custom-tilde-alist (or whatever technique you choose to keep the aliases in synch) as an exercise.

Answer 2

Simply use $foo instead of ~foo in the minibuffer. Emacs will treat foo as the name of an environment variable and use its value.