Populate repo with initial version
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README.md
58
README.md
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# direnv-cache
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## Setup
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direnv-cache consists of two components: the direnv-cache script and an
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extension to direnv's stdlib.
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To set up direnv-cache, make direnv read the provided direnvrc, eg. via
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cp direnvrc ~/.config/direnv/direnvrc
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and install direnv-cache somewhere in your PATH.
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If you use home-manager, you can add the following to your configuration
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...
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let
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direnv-cache = pkgs.callPackage ./path/to/this/repo {};
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in
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...
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home.packages = [ ... direnv-cache ... ];
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programs.direnv = {
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enable = true;
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enableBashIntegration = true;
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stdlib = builtins.readFile direnv-cache.direnvrc;
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};
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...
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## Usage
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The following assumes a working direnv setup.
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Use the cache function in your `.envrc` files, eg.
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cache <<EOF
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# everything in here will be cached
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use nix -p hello
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EOF
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# you can also have stuff outside the cached region
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export PATH=/some/other/path:$PATH
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If you now enter the directory, direnv will tell you that the environment
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is not yet cached. We can fix that by running `direnv-cache reload`. This
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will also tell direnv to reload. From now on, if you enter the directory,
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direnv will load the cached environment.
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Re-run `direnv-cache reload` whenever your `.envrc` or other dependencies change
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to update the cache.
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## How it works
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Everything piped into the `cache` function is stored in a recipe file in
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direnv-cache's cache directory when the `.envrc` is evaluated. Then, if the
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environment cache exists, it is sourced.
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When `direnv-cache reload` is called, it looks for a recipe file for the
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current directory, and runs it. A diff of the environments before and after the
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recipe is run is written to the directory-specific cache file.
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{ pkgs ? import <nixpkgs> {} }:
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(pkgs.writers.writeBashBin "direnv-cache" ./direnv-cache).overrideAttrs
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(o: { passthru = { direnvrc = ./direnvrc; }; })
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#!/usr/bin/env bash
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set -eo pipefail
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# Dumps all environment variables sorted alphabetically. Uses zero byte as a
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# delimiter since bash variables can not contain '\0'.
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dumpEnv() {
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env -0 | sort -z
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}
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# Retrieves the value of variable name passed as $1 in dumped environment
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# passed as $2 (see dumpEnv)
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getByName() {
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local name="$1"
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local envFile="$2"
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grep -z "^${name}=" $envFile | cut -z -f2- -d '=' | tr -d '\0'
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}
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# Produces a diff of two given environment dumps, suitable for consumption by
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# bash. Given environment dumps A and B (both generated by dumpEnv),
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#
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# source A; source <(diffEnvs A B)
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#
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# shall be equivalent to
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#
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# source B
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#
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diffEnvs() {
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local name
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local old="$1"
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local new="$2"
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while read -r -d '' line; do
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name=$(tr -d '\0' <<<"$line" | head -n1 | cut -f1 -d'=')
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if ! getByName "$name" "$new" >/dev/null; then
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echo "export -n '${name}'"
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fi
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done <"$old"
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while read -rd $'\0' line; do
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name=$(tr -d '\0' <<<"$line" | head -n1 | cut -f1 -d'=')
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if getByName "$name" "$old" >/dev/null; then
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# found in old env, check if values match
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if ! grep -z "^${line}\$" "$old" >/dev/null; then
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# variable has changed
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echo "export ${line@Q}"
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fi
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else
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# variable is new
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echo "export ${line@Q}"
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fi
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done <"$new"
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}
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usage() {
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echo "${BASH_SOURCE[0]} COMMAND"
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echo
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echo "Commands:"
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echo -e "\tstatus,s: Show cache status"
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echo -e "\treload,r: Recreate cache from .envrc"
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echo -e "\tclear,c: Remove cache file for current directory"
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}
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getCacheFilePath() {
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local cacheDir="${XDG_CACHE_HOME:-$HOME/.cache}/direnv-cache"
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echo "${cacheDir}/$(pwd | sha1sum | tr -d ' -')"
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}
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cmd="$1"
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if ! [[ -e .envrc ]]; then
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echo "Error, no .envrc found in current directory"
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exit 1
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fi
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cacheFile=$(getCacheFilePath)
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case $cmd in
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reload|r)
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echo "Re-creating cache"
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mkdir -p "$(dirname ${cacheFile})"
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dumpEnv > "${cacheFile}.pre"
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source <(direnv stdlib)
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if [[ .envrc -nt ${cacheFile}.recipe ]]; then
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direnv exec . true > /dev/null
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fi
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source "${cacheFile}.recipe"
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dumpEnv > "${cacheFile}.post"
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diffEnvs "${cacheFile}.pre" "${cacheFile}.post" > "$cacheFile"
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rm "${cacheFile}.pre" "${cacheFile}.post"
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echo "Environment cached in $cacheFile, telling direnv to reload"
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direnv reload
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;;
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status|s)
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shift
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ls "$cacheFile" "$@"
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;;
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clear|c)
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if [[ -e "$cacheFile" ]]; then
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rm "$cacheFile"
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fi
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;;
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*)
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usage
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exit 1
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esac
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# -*- mode: sh -*-
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cache() {
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local cacheDir="${XDG_CACHE_HOME:-$HOME/.cache}/direnv-cache"
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mkdir -p "$cacheDir"
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local cacheFile
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cacheFile="${cacheDir}/$(pwd | sha1sum | tr -d ' -')"
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cat - > "${cacheFile}.recipe"
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if [[ -e "$cacheFile" ]]; then
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echo "Using cached environment from $cacheFile"
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. $cacheFile
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else
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echo "Environment not cached"
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fi
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}
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