PATH and exec-path set, but emacs does not find executable

Question

My .emacs contains

(setenv "PATH" (concat ".:/usr/texbin:/opt/local/bin" (getenv "PATH")))
(setq exec-path (append exec-path '(".:/usr/texbin:/opt/local/bin")))

(add-to-list 'load-path "/usr/local/share/emacs/site-lisp")
(require 'tex-site)
(load "auctex.el" nil t t)
(load "preview-latex.el" nil t t)

/usr/texbin is where latex/pdflatex/.. are located. /opt/local/bin/ is where gs can be found.

And yet when I run preview-at-point, which apparently needs both latex and gs, I get

Preview-DviPS finished at Thu Dec 22 11:25:46
DviPS sentinel: Searching for program: No such file or directory, gs

which means that latex could be found all right, but not gs.

I am not sure whether setting exec-path is necessary, perhaps PATH is enough, but I've set it as a debugging measure.

Why can emacs not find gs even though the directory it's in is in both PATH and exec-path?

Answer 1

If you're setting $PATH inside your Emacs, you might well be on OS X. GUI applications are not started via your shell, so they see different environment variables.

Here's a trick which I use to ensure the $PATH inside Emacs is the same one I see if I fire up a terminal (but see "update" below):

(defun set-exec-path-from-shell-PATH ()
  "Set up Emacs' `exec-path' and PATH environment variable to match that used by the user's shell.

This is particularly useful under Mac OSX, where GUI apps are not started from a shell."
  (interactive)
  (let ((path-from-shell (replace-regexp-in-string "[ \t\n]*$" "" (shell-command-to-string "$SHELL --login -i -c 'echo $PATH'"))))
    (setenv "PATH" path-from-shell)
    (setq exec-path (split-string path-from-shell path-separator))))

Then simply call the set-exec-path-from-shell-PATH function, perhaps from your Emacs init file. I keep that code on github, BTW.

Update: this code has now been improved and published as an elisp library called exec-path-from-shell; installable packages are available in MELPA.