env.js

const fs = require('fs');
const qs = require('querystring');
const buf = fs.readFileSync('.env').toString();
const env = qs.parse(buf, "\n"); 

function getHash(env) {
  return new Promise((resolve, reject) => {
    require('child_process').exec('git rev-parse HEAD', (err, hash) => {
      if(err) return reject(err);
      env.COMMIT_HASH = hash;
      resolve(hash);
    });
  });
}

function dump() {
  Object.keys(env).forEach(k => { if(!k || k.length < 1 || !env[k]) delete env[k]; });
  fs.writeFileSync('.env', qs.stringify(env, "\n", "=", { 
    encodeURIComponent: function(x) { return x; } 
  }));
}

getHash(env)
  .then(_ => {
    dump();
  })
  .catch(err => {
    console.error(err.stack);
    process.exit(1);
  });