title: All the npm package not installed globally can't be executed directly
body: <h1>Symptom:</h1>
  
  <p>I can't execute the npm packages directly that are not installed globally. But I can execute it by <code>npm scripts</code>. How to fix it?</p>
  
  <p>For example:
  I installed <code>gulp</code> under the project: </p>
  
  <pre><code>npm install gulp --save-dev
  </code></pre>
  
  <p>Then I try to execute it by </p>
  
  <pre><code>gulp
  zsh: command not found: gulp
  </code></pre>
  
  <p>But if I add a <code>npm script</code> to <code>package.json</code>:</p>
  
  <pre><code>  "scripts": {
      "test": "mocha --require intelli-espower-loader &amp;&amp; gulp test",
      "start": "gulp"
    },
  </code></pre>
  
  <p>Then run </p>
  
  <pre><code>npm start
  </code></pre>
  
  <p>It can get executed without problem. </p>
  
  <p>P.S.
  Same issue with the <code>mocha</code> package, I can't execute <code>mocha</code> directly but I can execute <code>npm test</code> without problem.</p>
  
  <h1>Help Wanted:</h1>
  
  <p>What I can do to fix that issue?</p>
  
  <h1>Notice:</h1>
  
  <p>I'm not saying that I want to execute them globally, I just want to execute them under the project.</p>
  
  <p>I don't know where goes wrong, but they are executable not long ago, just don't work recently!</p>