I\'m trying to get a compile command (rake cucumber) to run with a specific ruby version on my Mac OS X system, I use rvm to do this currently in the terminal. My ~/.MacOSX/
I don't have a Mac, so I cannot test this directly, but this can all be found in the *info* page Interactive Inferior Shell.
When you start a shell in Emacs, the process that gets spawned is the program in the Emacs variable explicit-shell-file-name (and if that is nil, the environment variables ESHELL and SHELL are used).
It then sends the contents of ~/.emacs_*shellname* (e.g. if your shell is csh, then ~/.emacs_csh would be sent over. Also, the appropriate .rc files for csh program is sourced, so you can update that as well (in my case .cshrc). Additionally, you can wrap customizations in the .rc file with a check for the environment variable INSIDE_EMACS (which which Emacs sets before it runs a shell).
You need to update those files to change the path in the shell, not the Emacs variable exec-path. exec-path - which is just a list of directories Emacs uses to find executable programs. The behavior of the executables are not affected by changes to exec-path.