GNU ELPA - buffer-env


Buffer-local process environments
buffer-env-0.3.tar, 2022-Mar-25, 30.0 KiB
Augusto Stoffel <>
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To install this package, run in Emacs:

M-x package-install RET buffer-env RET

Full description


With this package, you can teach Emacs to call the correct version of external programs such as linters, compilers and language servers on a per-project basis. Thus you can work on several projects in parallel with no undue interference and switch seamlessly between them.

1 Basic setup

1.1 On the project side

Your project settings should go into a shell script named .envrc which exports a suitable PATH, as well as any other desired environment variables. Place this script at the root directory of your project.

This follows the approach of the popular direnv program, and is mostly compatible with it. However, buffer-env is entirely independent of direnv so it is not possible to use direnv-specific features in the .envrc scripts — at least not directly.

Alternatively, it is possible to configure buffer-env to directly support other environment setup methods, such as Python virtualenvs or .env files. See below for details.

1.2 On the Emacs side

The usual way to activate this package in Emacs is by including the following in your init file:

(add-hook 'hack-local-variables-hook 'buffer-env-update)

In this way, any buffer potentially affected by directory-local variables will also be affected by buffer-env. It is also possible to add buffer-env-update only to specific major-mode hooks, or call it interactively.

2 How this package works

When called interactively, buffer-env-update asks for a script file and executes it (in the sense detailed below). The role of the script is to set some environment variables. Then the Emacs variables process-environment and exec-path are made buffer-local and their values are set so as to replicate the environment defined by the script.

When buffer-env-update is called from a hook, a file named buffer-env-script-name is looked up in the current directory or one of its parents. If found, the same procedure as in the interactive case takes place. Otherwise, nothing happens.

It remains to clarify what “executing a script” means in the paragraphs above. Normally, it simply means to execute the script as a shell script and collect all the exported variables. However, certain script names are treated specially. These are:

  • .env: These files, used by Docker, Node.js and others, are simple lists of VARIABLE=value pairs. They are still executed as shell scripts (which dictates when and how quotes are to be used, for instance), but no export statements are needed.
  • guix.scm: The development environment of the Guix package is loaded and exported to Emacs. Make sure you have entered guix shell at least once before to install the dependencies, otherwise you may block Emacs for a long time.

For instructions on how to extend this list, see the documentation of the variable buffer-env-commands.

3 Integration with other environment management mechanisms

3.1 Python virtualenvs

In most cases, the easiest way to interface with Python virtualenvs is to create an .envrc file with the following contents:

source path-to-virtualenv/bin/activate

You can also call buffer-env-activate interactively and select the activate script directly.

However, if you want to avoid writing .envrc scripts and you create virtualenvs in a predictable place, say in a .venv directory at the root of each project, you can say

(setq buffer-env-script-name ".venv/bin/activate")

or a variation thereof. Note that it is also possible to provide an absolute path for buffer-env-script-name, and it is possible to specify it as a buffer- or directory-local variable.

3.2 .env files

To load the environment defined by a .env file, you can select it interactively with buffer-env-update. To automate the process, set buffer-env-script-name to ".env", either globally, dir-locally or buffer-locally.

3.3 Direnv

Buffer-env is mostly compatible with direnv; specifically, it assumes .envrc is a regular shell script, so you can't directly use anything from direnv's library of helper functions. A workaround is to use the following configuration:

(with-eval-after-load 'buffer-env
  (add-to-list 'buffer-env-commands '(".envrc" . "direnv exec . env -0")))

If you need tighter integration with direnv, you may want to check out the envrc package.

4 Compatibility issues

Most Emacs packages are not written with the possibility of a buffer-local process environment in mind. This leads to issues with a few commands; specifically, those which start an external process after switching to a different buffer or remote directory. Examples include:

  • shell, project-shell (C-x p s) and other REPLs;
  • compile and project-compile (C-x p c) in Emacs 27 and older;
  • async-shell-command (M-&).

Fortunately, the problem has an easy fix provided by the inheritenv package, which see.

Alternatively, if you speak Elisp and want to keep your configuration lean, you can just copy the function below and apply it as an :around advice to any affected commands.

(defun buffer-env-inherit (fn &rest args)
  "Call FN with ARGS using the buffer-local process environment.
Intended as an advice around commands that start a process after
switching buffers."
  (cl-letf (((default-value 'process-environment) process-environment)
	    ((default-value 'exec-path) exec-path))
    (apply fn args)))

4.1 Non-Unix-like systems

Currently, this package assumes your system shell is POSIX. For other types of operating system, I would need to know what the appropriate value of buffer-env-commands is. Drop me a line if you can help.

5 Related packages

This package is essentially a knockoff of the envrc package by Steve Purcell. The main difference is that envrc depends on and tightly integrates with the direnv program, while buffer-env is minimalist and has no extra dependencies.

For a comparison of the buffer-local approach to environment variables with the global approach used by most of the similar packages, see envrc's design notes.

There is a large number of Emacs packages interfacing with the Python virtualenv system. They all seem to take the global approach and, therefore, the comparisons and caveats in the envrc design notes also apply, mutatis mutandis.

6 Contributing

Discussions, suggestions and code contributions are welcome! Since this package is part of GNU ELPA, contributions require a copyright assignment to the FSF.

Old versions

buffer-env-0.2.tar.lz2022-Feb-285.58 KiB