Parse an env string (printenv output)

#parseEnv.ts

import assert from 'node:assert/strict';

/**
 * Parses a string containing environment variables and returns a map of key => value pairs.
 *
 * The string format is `KEY=VALUE` pairs separated by new lines;
 * it typically comes from UNIX command `printenv` or `env`.
 */
export function parseEnv(env: string) {
  const lines = env
    .split('\n')
    // Trim lines
    .map(line => line.trim())
    // Remove empty lines
    .filter(line => line !== '')
    // Remove commented lines
    .filter(line => !line.startsWith('#'));

  const envMap = new Map();

  for (const line of lines) {
    const result = /^(.+)=(.*)$/.exec(line);
    assert(result !== null, `Invalid line '${line}'`);
    const key = result[1];
    const value = result[2];
    envMap.set(key, value);
  }

  return envMap;
}

parseEnv.test.ts

import { expect, test } from 'vitest';

import { parseEnv } from './parseEnv';

test('parse printenv output', () => {
  const env = `
    SHELL=/bin/zsh
    HOME=/Users/username
    LOGNAME=username
    USER=username
    PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/Apple/usr/bin

    # This is a comment

    DOUBLE_QUOTES="value with double quotes"
    SINGLE_QUOTES='value with single quotes'

    NO_VALUE=

    SPACES= value  with   spaces

    EQUAL=value with = equal sign

    HASH=value with # number sign
    `;

  expect(Object.fromEntries(parseEnv(env).entries())).toEqual({
    SHELL: '/bin/zsh',
    HOME: '/Users/username',
    LOGNAME: 'username',
    USER: 'username',
    PATH: '/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/Apple/usr/bin',
    DOUBLE_QUOTES: '"value with double quotes"',
    SINGLE_QUOTES: "'value with single quotes'",
    NO_VALUE: '',
    SPACES: ' value  with   spaces',
    'EQUAL=value with ': ' equal sign',
    HASH: 'value with # number sign'
  });
});

test('fail when parsing a malformed env string', () => {
  expect(() => parseEnv(`=no key`)).toThrow("Invalid line '=no key'");
  expect(() => parseEnv(`=`)).toThrow("Invalid line '='");
});