title: sort -un removing non-matching lines
body: <p>Whenever I am using <code>sort -un</code> function on this specific text file it removes certain values. Now <code>-n</code> is numeric sort, and <code>-u</code> is remove duplicates, I see no reason why it should remove those entries with only open port.</p>
  
  <pre><code>aaa@aaa cat test 
  All 1500 scanned ports on 10.10.10.10 are open|filtered
  161/udp  open|filtered snmp
  161/udp   open          snmp
  161/udp   open          snmp
  161/udp  open          snmp
  
  aaa@aaa cat test | sort -un
  All 1500 scanned ports on 10.10.10.10 are open|filtered
  161/udp  open|filtered snmp
  </code></pre>
  
  <p>Any ideas why is sort function having this weird bahaviour? I would exptect <code>sort -un</code> would be the same as <code>sort -n file | sort -u</code></p>