Find out the differences between multiple .env

diff-env.js

/**
 * Imports
 */
const fs = require('fs');

/**
 * Extract env keys from env content
 */
function parseEnv(envContent) {
  const lines = envContent.split('\n');
  const vars = lines.filter(line => line.trim() && !line.startsWith('#'));
  const keys = vars.map(v => v.split('=')[0]);
  return keys;
}

/**
 * Read file and return parsed env
 */
function parseFile(filePath) {
  return new Promise((resolve, reject) => {
    fs.readFile(filePath, (err, data) => {
      if (err) {
        reject(err);
      } else {
        resolve(parseEnv(data.toString('utf8')));
      }
    });
  });
}

/**
 * Return additionnal keys for this array compared to others
 */
Array.prototype.additionnal = function(...arrs) {
  let keys = new Set();
  for (let arr of arrs) {
    if (arr !== this) {
      for (let key of arr) {
        keys.add(key);
      }
    }
  }
  keys = Array.from(keys);
  return this.filter(key => !keys.includes(key));
};

/**
 * Return missing keys for this array compared to others
 */
Array.prototype.missing = function(...arrs) {
  let keys = new Set();
  for (let arr of arrs) {
    if (arr !== this) {
      for (let key of arr) {
        keys.add(key);
      }
    }
  }
  return Array.from(keys).filter(key => !this.includes(key));
};

/**
 * Check differences for every array
 */
function diffArray(...arrs) {
  return arrs.map(arr => ({
    additionnal: arr.additionnal(...arrs),
    missing: arr.missing(...arrs),
  }));
}

/**
 * Starting point, read argv, process differences and print!
 */
const entryFiles = process.argv.slice(2);
Promise.all(entryFiles.map(parseFile))
  .then(files => diffArray(...files))
  .then(results => {
    for (let i = 0; i < results.length; i++) {
      console.log('>>> %s <<<', process.argv[i + 2]);
      console.log(results[i]);
    }
  });

run.sh

# Usage node diff-env.js [...env files]
node diff-env.js .env.example .env
node diff-env.js .env.example .env .env.development .env.production

# Example output with .env.example and .env
# >>> .env.example <<<
# {
#   additionnal: [
#     'CREDENTIALS'
#   ],
#   missing: [
#     'NEW_FEATURE_ENV'
#   ],
# }
# >>> .env <<<
# {
#   additionnal: [
#     'NEW_FEATURE_ENV'
#   ],
#   missing: [
#     'CREDENTIALS'
#   ],
# }