title: How to retrieve unique IDs from the txt file?
body: <p>I have a text file containing the sequence IDs. These Ids file contain some duplicate IDs. Few IDs are also present more then 2 times in this file. I want to find  unique IDs in one file and repeated IDs in another file. Furthermore I am also interested to find the number, how many times the repeated IDs present in the file.</p>
  
  <p>I found duplicated sequence using the following command</p>
  
  <pre><code>$ cat id.txt | grep '^&gt;' | sort | uniq -d &gt; dupid.txt
  </code></pre>
  
  <p>This gives me the duplicated sequences in "dupid.txt" file. But how do I get those that are present more then 2 times and how many times they are present? Secondly, how do I find unique sequences?</p>