src/lib/cross-conf-env.js

import Spawn from 'cross-spawn';

/**
 * Select the key of the value to be replaced from "process.env".
 *
 * @return {Array.<String>} Keys.
 */
export function FilterKeys() {
  return Object
  .keys( process.env )
  .filter( ( key ) => {
    return (
      key && typeof key === 'string' &&
      ( key.indexOf( 'npm_package_' ) !== -1 || key.indexOf( 'npm_config_' ) !== -1 )
    );
  } )
  .sort( ( a, b ) => {
    // Processing the variables with the same prefix in the correct order.
    // "npm_package_config_NAME_NAME2" contained in "npm_package_config_NAME"
    // is in descending order by the length to prevent from being replace earlier.
    //
    return ( b.length - a.length );
  } );
}

/**
 * Replace the arguments in the value of "process.env".
 *
 * @param {Array.<Object>} argv Arguments of the command line.
 * @param {Array.<Object>} keys The filtered key ( "npm_package_" or "npm_config_" ) of "process.env".
 *
 * @return {Array.<String>} Augments.
 */
export function ReplaceArgv( argv, keys ) {
  if( keys.length === 0 ) { return argv; }

  return argv.map( ( arg ) => {
    let newArg = arg;
    keys.forEach( ( key ) => {
      const pettern = '%' + key + '%|\\$' + key + '|' + key;
      const regexp  = new RegExp( pettern );
      if( regexp.test( newArg ) ) {
        newArg = newArg.replace( regexp, String( process.env[ key ] ) );
      }
    } );

    return newArg;
  } );
}

/**
 * Replace the value of the command line arguments in process.env,
 * and run the process with a replaced arguments.
 *
 * @param {Array.<Object>} argv Arguments of the command line.
 *
 * @return {Object} Process.
 */
export default function CrossConfEnv( argv ) {
  const newArgv = ReplaceArgv( argv, FilterKeys() );
  if( !( newArgv && 0 < newArgv.length ) ) { return process.exit(); }

  const command = newArgv.shift();
  const proc    = Spawn( command, newArgv, { stdio: 'inherit' } );

  proc.on( 'exit', process.exit );

  return proc;
}