This variable is the equivalent of the PATH environment variable for Emacs. It contains a list of directories Emacs will search for executables.

Here’s an example of appending the /sw/bin directory to the exec-path and PATH variables (useful for Mac OS X users running LaTeX):

    (setenv "PATH" (concat (getenv "PATH") ":/sw/bin"))
    (setq exec-path (append exec-path '("/sw/bin")))


I found there are difference between exec-path and PATH.

Aborn Jiang