title: how to use kubectl command with flag --selector?
body: <p>I have a question about kubectl command with flag --selector. In help menu it says,</p>
  
  <pre><code>-l, --selector="": Selector (label query) to filter on
  </code></pre>
  
  <p>how ever it does't work as i expect, 
  for example, i want to get RC who have selector like</p>
  
  <pre><code>    "spec": {
      "replicas": 2,
      "selector": {
          "app": "tas-core"
      },
  </code></pre>
  
  <p>when i give command</p>
  
  <pre><code>kubectl get pod --selector="app:tas-core"
  </code></pre>
  
  <p>system report: the provided selector "app:tas-core" is not valid: unable to parse requirement: label key: invalid value 'app:tas-core', Details: must match regex [a-z0-9?(.a-z0-9?)* / ] a-z0-9?</p>
  
  <p>after i check the regexp </p>
  
  <pre><code>[[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)* / ] [a-z0-9]([-a-z0-9]*[a-z0-9])?
  </code></pre>
  
  <p>i still can't find any string which can pass the regexp!
  i gave,</p>
  
  <pre><code>kubectl get rc -l app/tas-core
  </code></pre>
  
  <p>nothing has been returned.
  How could i use it?</p>
  
  <p>I have also another question, how to filter all pods which with label like</p>
  
  <pre><code>"labels": {
    "app": "tas-core"
  }
  </code></pre>
  
  <p>?  </p>