Initial commit: Go clone of daemontools envdir

.gitignore

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+envdir

LICENSE

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+MIT License
+
+Copyright (c) 2026 Jeffrey Paul
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# envdir
+
+A Go clone of the [daemontools](https://cr.yp.to/daemontools.html) `envdir`
+program.
+
+## Install
+
+```
+go install sneak.berlin/go/envdir@latest
+```
+
+## Usage
+
+```
+envdir dir child [args...]
+```
+
+`envdir` sets various environment variables as specified by files in `dir`,
+then runs `child` with the given arguments.
+
+If `dir` contains a file named `FOO` whose first line is `bar`, `envdir`
+sets the environment variable `FOO` to `bar`, then runs `child`.
+
+### Rules
+
+- Each file in `dir` corresponds to one environment variable. The filename
+  is the variable name and the first line of the file is the value.
+- If a file is empty, the corresponding variable is **unset**.
+- NUL bytes (`\0`) in file contents are replaced with newlines.
+- Trailing spaces and tabs are stripped from the value.
+- Lines after the first newline are ignored.
+- Subdirectories and files with `=` in the name are skipped.
+- Exit code is **111** if `envdir` encounters an error.
+
+## Example
+
+```
+$ mkdir /tmp/env
+$ echo -n "production" > /tmp/env/APP_ENV
+$ echo -n "localhost:5432" > /tmp/env/DB_HOST
+$ envdir /tmp/env printenv APP_ENV
+production
+```
+
+## License
+
+MIT

go.mod

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+module sneak.berlin/go/envdir
+
+go 1.25.5

main.go

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+package main
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+)
+
+func main() {
+	if len(os.Args) < 3 {
+		fmt.Fprintf(os.Stderr, "usage: envdir dir child\n")
+		os.Exit(111)
+	}
+
+	dir := os.Args[1]
+	child := os.Args[2]
+	childArgs := os.Args[2:]
+
+	env, err := buildEnv(dir)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "envdir: %s\n", err)
+		os.Exit(111)
+	}
+
+	path, err := findExecutable(child)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "envdir: %s\n", err)
+		os.Exit(111)
+	}
+
+	err = syscall.Exec(path, childArgs, env)
+	fmt.Fprintf(os.Stderr, "envdir: exec: %s\n", err)
+	os.Exit(111)
+}
+
+func buildEnv(dir string) ([]string, error) {
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return nil, fmt.Errorf("unable to read directory %s: %w", dir, err)
+	}
+
+	// Start with the current environment.
+	envMap := make(map[string]string)
+	unset := make(map[string]bool)
+	for _, e := range os.Environ() {
+		k, v, _ := strings.Cut(e, "=")
+		envMap[k] = v
+	}
+
+	for _, entry := range entries {
+		name := entry.Name()
+
+		// Skip subdirectories.
+		if entry.IsDir() {
+			continue
+		}
+
+		// Skip names containing '='.
+		if strings.Contains(name, "=") {
+			continue
+		}
+
+		path := filepath.Join(dir, name)
+		data, err := os.ReadFile(path)
+		if err != nil {
+			return nil, fmt.Errorf("unable to read %s: %w", path, err)
+		}
+
+		// If the file is empty, unset the variable.
+		if len(data) == 0 {
+			delete(envMap, name)
+			unset[name] = true
+			continue
+		}
+
+		// Use only the first line.
+		if i := bytes.IndexByte(data, '\n'); i >= 0 {
+			data = data[:i]
+		}
+
+		// Replace NUL bytes with newlines.
+		data = bytes.ReplaceAll(data, []byte{0}, []byte{'\n'})
+
+		// Trim trailing spaces and tabs.
+		value := strings.TrimRight(string(data), " \t")
+
+		envMap[name] = value
+		delete(unset, name)
+	}
+
+	env := make([]string, 0, len(envMap))
+	for k, v := range envMap {
+		env = append(env, k+"="+v)
+	}
+	return env, nil
+}
+
+func findExecutable(name string) (string, error) {
+	// If name contains a slash, use it directly.
+	if strings.Contains(name, "/") {
+		return name, nil
+	}
+
+	// Search PATH.
+	pathEnv := os.Getenv("PATH")
+	for _, dir := range filepath.SplitList(pathEnv) {
+		path := filepath.Join(dir, name)
+		info, err := os.Stat(path)
+		if err != nil {
+			continue
+		}
+		if info.Mode().IsRegular() && info.Mode()&0111 != 0 {
+			return path, nil
+		}
+	}
+	return "", fmt.Errorf("command not found: %s", name)
+}