Requires GNU grep

[tviti]

Issue

This isn't really an issue with nix-direnv, but more of a caveate I encountered when trying to use nix-direnv on macOS. I first encountered this using direnv-mode in emacs w/ nix-direnv on macOS, but it looks like it's also a problem just using direnv from bash on macOS.

From a directory that DOESN'T have a cached environment (i.e. .direnv either doesn't exist or is empty), the following error is shown when making a first attempt at loading the env:

usage: grep [-abcDEFGHhIiJLlmnOoqRSsUVvwxZ] [-A num] [-B num] [-C[num]]
	[-e pattern] [-f file] [--binary-files=value] [--color=when]
	[--context[=num]] [--directories=action] [--label] [--line-buffered]
	[--null] [pattern] [file ...]

which results in the creation of an empty cache.

Setup

Directory structure:

nix-direnv-test taylor$ ls -la
total 16
drwxr-xr-x   5 taylor  staff   160 Mar 10 11:26 .
drwxr-xr-x  55 taylor  staff  1760 Mar 10 11:24 ..
drwxr-xr-x   3 taylor  staff    96 Mar 10 11:26 .direnv
-rw-r--r--   1 taylor  staff     8 Mar 10 11:24 .envrc
-rw-r--r--   1 taylor  staff    87 Mar 10 11:25 shell.nix

.direnv:

use nix

shell.nix:

let pkgs = import <nixpkgs> { };
in pkgs.mkShell {
    buildInputs = [ pkgs.hello ];
}

Steps to reproduce

nix-direnv-test taylor$ direnv allow
direnv: loading ~/Source/nix-direnv-test/.envrc
direnv: using nix
usage: grep [-abcDEFGHhIiJLlmnOoqRSsUVvwxZ] [-A num] [-B num] [-C[num]]
	[-e pattern] [-f file] [--binary-files=value] [--color=when]
	[--context[=num]] [--directories=action] [--label] [--line-buffered]
	[--null] [pattern] [file ...]

Fix

The issue seems to be that nix-direnv is trying to invoke the macOS builtin BSD-grep at /usr/bin/grep, which for one reason or another doesn't like (in direnvrc):

    tmp=$(nix-shell --show-trace --pure "$@" --run "$dump_cmd" \
              | grep -oP '(?<=_____direnv_____).*')

I haven't actually spent any time trying to figure out WHY that line is problematic with the builtin grep, but I managed to sort this out by installing nix-direnv with the following derivation, which explicitely uses nixpkgs.gnugrep

{ bash, fetchFromGitHub, gnugrep, stdenv }:

stdenv.mkDerivation {
  name = "nix-direnv";

  src = fetchFromGitHub {
    owner = "nix-community";
    repo = "nix-direnv";
    rev = "81d3f5083ae68aec5d9f6fc9eebac57c82a9d280";
    sha256 = "067493hbsij59bvaqi38iybacqbzwx876dvdm651b5mn3zs3h42c";
  };

  phases = [ "unpackPhase" "patchPhase" "installPhase" ];

  prePatch = ''
    substituteInPlace direnvrc --replace "/usr/bin/env bash" "${bash}/bin/bash"
    substituteInPlace direnvrc --replace "grep" "${gnugrep}/bin/grep"
  '';
  
  installPhase = ''
    mkdir -p $out/share/nix-direnv
    cp -rv ./* $out/share/nix-direnv
  '';
}

[Mic92]

Interesting. I might be able to replace this invocation with an awk call that should be portable. Do you now if nix show-derivation $out | grep -E -o -m1 '/nix/store/.*.drv' is problematic with bsdgrep?

[Mic92]

@zimbatm does direnv on macOS uses the builtin bash btw? Because that might also cause problems.

[Mic92]

Replacing /usr/bin/env bash should not have any effect because direnv executes the bash version itself.

[zimbatm]

yes... direnv uses whatever bash is in the environment

[Mic92]

In that case I should suggest people to install direnv via nixpkgs or get a newer version via $packagemanager. I have not tested bash compatibility though.

[zimbatm]

The one that comes from nixpkgs is bound to the nixpkgs bash at compile time.

[zimbatm]

Anyone using Homebrew should also brew install bash

[Mic92]

It would be great if direnv would have something like a .direnv.d or even environment variables to load third party plugins. I think it is time to package nix-direnv in nixpkgs itself.

[Mic92]

Can we convince the homebrew maintainers to also hard code bash? https://github.com/Homebrew/homebrew-core/blob/master/Formula/direnv.rb#L18

[zimbatm]

@Mic92 direnv looks in ~/.config/direnv/lib/*.sh for additional libs. (since v2.21)

[Mic92]

Ok. This would not play well with vanilla nix or most other system package manager in that regard, but a home-manager module could work.

[Mic92]

Nix-direnv can now be installed via nix. This version will hard code nix as well as gnugrep.