code: function run(env) {
    console.log(); // empty line
    var verbfile = env.configPath;
  
    if (versionFlag && tasks.length === 0) {
      verbLog('CLI version', pkg.version);
      if (env.modulePackage && typeof env.modulePackage.version !== 'undefined') {
        verbLog('Local version', env.modulePackage.version);
      }
    }
  
    // `node_modules/verb`
    if (!env.modulePath || !fs.existsSync(env.modulePath)) {
      /* deps: verb */
      env.modulePath = resolve.sync('verb');
    }
  
    // chdir before requiring `verbfile.js` to allow users to chdir as needed
    if (process.cwd() !== env.cwd) {
      process.chdir(env.cwd);
      verbLog('working directory changed to', tildify(env.cwd));
    }
  
    // require verb
    var verbInst = require(env.modulePath);
    verbInst.extend('argv', argv);
    verbInst.emit('loaded');
  
    if (!argv._.length && argv.no) {
      exit(0);
    }
  
    // `verbfile.js`
    if ((hasVerbmd && !hasVerbfile) || !verbfile) {
      verbfile = resolve.sync('verb-default');
      env.configBase = path.dirname(env.configBase);
      require(verbfile)(verbInst);
    } else {
      // this is what actually loads up the verbfile
      require(verbfile);
    }
  
    verbLog('using verbfile', tildify(verbfile));
    logEvents(verbInst);
  
    process.nextTick(function () {
      if (simpleTasksFlag) {
        return logTasksSimple(env, verbInst);
      }
      if (tasksFlag) {
        return logTasks(env, verbInst);
      }
  
      verbInst.run(toRun, function (err) {
        if (err) console.error(err);
      });
    });
  }
docs: the actual logic