在Google上也没有找到相关的解释，请问 ._. 这是种什么用法？

const path = require('path');//nodejs module 
const args = require('minimist')(process.argv.slice(2));
// List of allowed environments
const allowedEnvs = ['dev', 'dist', 'test'];
// Set the correct environment
var env;
if(args._.length > 0 && args._.indexOf('start') !== -1) {
  env = 'test';
} else if (args.env) {
  env = args.env;
} else {
  env = 'dev';
}
process.env.REACT_WEBPACK_ENV = env;