Can Emacs detect the path of its executable?

Question

Suppose that I have two identical emacs (of the same version) on my system. One is placed at C:\Program Files\Gnu Emacs and the other one at different place, say C:\Program Files\New Gnu Emacs. Can a running Emacs detect which one is? For example, can it give the path of its executable (i.e., the path where emacs.exe or emacs.bin can be found)?

Answer 1

Assuming Emacs knows how it was started, you can access the full path of the executable file by doing:

(expand-file-name invocation-name invocation-directory)

In my system, for instance, this returns "/usr/local/bin/emacs" on my regular session and returns "~/.evm/bin/emacs" on my evm test session. If you want to get fancy, you can also wrap that in a file-truename to resolve any symlinks.

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The two variables used above, as described by their doc strings:

• invocation-name

  The program name that was used to run Emacs.
  Any directory names are omitted.

• invocation-directory

  The directory in which the Emacs executable was found, to run it.
  The value is nil if that directory's name is not known.