title: sed with regular expression
body: <p>I am trying to replace three letter code at the end of a sequence with nothing (basically removing) with <code>sed</code> but is not working well for multiple regex pattern. Here is an example of sequences</p>
  
  <pre><code>GCAAAAAGTTGTATAGTCACACAACCTAGACTTATATCGTCTGCTATTCATTAG
  GCAAAAAGTTGTATAGTCACACAACCTAGACTTATATCGTCTGCTATTCATTAA
  GCAAAAAGTTGTATAGTCACACAACCTAGACTTATATCGTCTGCTATTCATTGA
  </code></pre>
  
  <p>When I try to use <code>regex</code> individually with <code>sed</code> it works</p>
  
  <pre><code>echo "GCAAAAAGTTGTATAGTCACACAACCTAGACTTATATCGTCTGCTATTCATTAG" | sed 's/TAG$//'
  echo "GCAAAAAGTTGTATAGTCACACAACCTAGACTTATATCGTCTGCTATTCATTAA" | sed 's/TAA$//'
  echo "GCAAAAAGTTGTATAGTCACACAACCTAGACTTATATCGTCTGCTATTCATTAG" | sed 's/TAG$//'
  </code></pre>
  
  <p>However when I try to include multiple regex it doesn't work</p>
  
  <pre><code>echo "GCAAAAAGTTGTATAGTCACACAACCTAGACTTATATCGTCTGCTATTCATTAG" |
  sed 's/(TAG$|TAA$|TGA$)//'
  </code></pre>
  
  <p>Could somebody point to me where I am doing wrong?</p>