envel

Introduction

envel is a utility to record environment variables in a form that can be easily read by Emacs. It’s written in C++ so that it can be run during shell initialization without noticable impact.

It’s used to make Emacs load shell environment variables even when it is not launched from a shell. See this article for an explanation.

Installation

You need a recent version of cmake and a C++ compiler to compile envel:

scripts/configure-release
scripts/build

Then copy build/src/gen-envel to a directory in your $PATH, for example ~/.local/bin.

Usage

Add the following to your shell initialization file (assuming gen-envel is in your $PATH). Change the --vars= list to the variables you need in Emacs.

if command -v gen-envel >/dev/null 2>&1; then
    gen-envel --vars PATH http_proxy https_proxy all_proxy SSH_AUTH_SOCK \
              SSH_AGENT_PID --output ~/.emacs.d/.local/env.el
fi

Add the following snippet to your Emacs initialization file:

(defun load-env-file (file)
  "Read and set envvars from FILE."
  (if (null (file-exists-p file))
      (signal 'file-error
              (list "No envvar file exists." file
                    "See https://github.com/hjiang/envel."))
    (with-temp-buffer
      (insert-file-contents file)
      (when-let (env (read (current-buffer)))
        (let ((tz (getenv-internal "TZ")))
          (setq-default
           process-environment
           (append env (default-value 'process-environment))
           exec-path
           (append (split-string (getenv "PATH") path-separator t)
                   (list exec-directory))
           shell-file-name
           (or (getenv "SHELL")
               (default-value 'shell-file-name)))
          (when-let (newtz (getenv-internal "TZ"))
            (unless (equal tz newtz)
              (set-time-zone-rule newtz))))
        env))))

(let ((env-file "~/.emacs.d/.local/env.el"))
  (when (file-readable-p env-file)
    (defun reload-env ()
      "Reload environment variables"
      (interactive)
      (load-env-file env-file))
    (reload-env)))

If ~/.emacs.d/.local/ does not exist, you have to create it first. During a long-running Emacs session, you can use M-x reload-env to reload the env file.