bug#14110: 24.3.50; Add command to open files outside of Emacs (use xdg-open, open etc)

[Stefan Monnier]

> Leo suggests `dired-guess-shell-alist-user'.  COMMAND there is a sexp,
> btw. So the above variable is also evil.

Yes.  I also plead guilty of doing that a few times in the past.
It's still evil.

> There is one another reason why `dired-guess-shell-alist-user' will be
> improper to be used for Open semantics.  IIRC, running a shell command
> .tex file compiles it.  So equating shell command with open is
> confusing, btw.

I tend to agree, but:
- I can't think of anything useful "open" could do with a .tex file
  other than pass it back to Emacs (which you can already do better by
  opening the file in Emacs without going through "open").
  While this might not apply to all cases, I suspect that most cases are
  like that.
- That doesn't preclude using dired-guess-shell.  It might just mean
  that we should have maybe an alist for "run command" and another alist
  for "open command" (and maybe a third alist to share the many common
  cases between the two).


        Stefan