title: Why does tr -d replace the target with -?
body: <p>According to the tr man:</p>
  
  <p>-d, --delete            delete characters in SET1, do not translate</p>
  
  <p>However</p>
  
  <pre><code>$ echo "abc" | tr "a" -d 
  -bc
  </code></pre>
  
  <p>Now this could be removed with an additional command such as </p>
  
  <pre><code>echo "abc" | tr "a" -d | sed 's/-//'
  </code></pre>
  
  <p>but am I missing something here?  Why does delete do a replace with - ?</p>