File & Pathflags: m

.env File Key-Value Line

Parse KEY=value lines from .env config files, handling quoted values and trailing comments.

Available in

JavaScript / ECMAScript code

jsJavaScript

const re = new RegExp("^([A-Z_][A-Z0-9_]*)\\s*=\\s*(?:\"([^\"]*)\"|'([^']*)'|([^#\\s]*))(?:\\s*#.*)?$", "m");
const input = "DATABASE_URL=postgres://localhost/db";
const matches = [...input.matchAll(re)];
console.log(matches.map(m => m[0]));

Uses `String.prototype.matchAll` for global iteration (Node 12+ / all modern browsers).

Python (re) code

pyPython

import re

pattern = re.compile(r"^([A-Z_][A-Z0-9_]*)\\s*=\\s*(?:\"([^\"]*)\"|'([^']*)'|([^#\\s]*))(?:\\s*#.*)?$", re.MULTILINE)
input_text = "DATABASE_URL=postgres://localhost/db"
for m in pattern.finditer(input_text):
    print(m.group(0))

Stdlib `re` module — no third-party dependency. Works on Python 3.6+.

Go (RE2) code

goGo

package main

import (
	"fmt"
	"regexp"
)

func main() {
	re := regexp.MustCompile(`(?m)^([A-Z_][A-Z0-9_]*)\s*=\s*(?:"([^"]*)"|'([^']*)'|([^#\s]*))(?:\s*#.*)?$`)
	input := `DATABASE_URL=postgres://localhost/db`
	for _, match := range re.FindAllString(input, -1) {
		fmt.Println(match)
	}
}

Uses `regexp.MustCompile` (panics on bad patterns at startup) and `FindAllString` for all matches.

Pattern

regexengine-agnostic

^([A-Z_][A-Z0-9_]*)\s*=\s*(?:"([^"]*)"|'([^']*)'|([^#\s]*))(?:\s*#.*)?$   (flags: m)

Raw source: ^([A-Z_][A-Z0-9_]*)\s*=\s*(?:"([^"]*)"|'([^']*)'|([^#\s]*))(?:\s*#.*)?$

How it works

([A-Z_][A-Z0-9_]*) captures the variable name (uppercase + underscores by convention). The value alternation supports double-quoted, single-quoted, and unquoted values. (?:\s*#.*)? allows an optional inline comment. The m flag lets ^ and $ match individual lines in a multi-line file.