equivalent of unix "which" for exec-path?

Question

I am trying to debug some bizarre issues with my exec-path settings.

When I debug PATH in shell, the key tool is "which", which tells me the absolute path we resolve for a given binary, i.e.

(701) % which ifconfig
/sbin/ifconfig

Is there some equivalent to tell me, for example, what binary Tramp will get when it asks to execute "ssh"?

Answer 1

You can attempt locating an executable in exec-path with executable-find:

(executable-find "ls") ;=> "/usr/bin/ls"
(executable-find "sl") ;=> nil

Answer 2

Tramp provides a debugging buffer, usually *debug tramp...* that provides a lot of information. For example...

;; GNU Emacs: 24.4.51.2 Tramp: 2.2.9-24.4 -*- mode: outline; -*-
17:54:29.340451 tramp-maybe-open-connection (3) # Opening connection for schwern.net using scp...
17:54:29.369182 tramp-maybe-open-connection (3) # Sending command `exec ssh   -o ControlPath=/var/folders/0b/7xp2lxbd7yl0tcpms06fr3d40000gn/T/tramp.40010Dqz.%r@%h:%p -o ControlMaster=auto -o ControlPersist=no -e none schwern.net'

You can see, it's running exec ssh which will pick up the normal ssh from your PATH. If you want to be sure you can run M-x shell and check which ssh or use the commands in @wasamasa's answer.

What tramp will use to login is controlled by the tramp-login-program argument to the particular method in the tramp-methods variable. For example, here's the ssh method.

 ("ssh"
  (tramp-login-program "ssh")
  (tramp-login-args
   (("-l" "%u")
    ("-p" "%p")
    ("%c")
    ("-e" "none")
    ("%h")))
  (tramp-async-args
   (("-q")))
  (tramp-remote-shell "/bin/sh")
  (tramp-remote-shell-args
   ("-c"))
  (tramp-gw-args
   (("-o" "GlobalKnownHostsFile=/dev/null")
    ("-o" "UserKnownHostsFile=/dev/null")
    ("-o" "StrictHostKeyChecking=no")))
  (tramp-default-port 22))