title: sed on OS X - can't seem to use + in regexps
body: <p>Now according to all the literature</p>
  
  <pre><code>echo 1234abcd|sed "s|[0-9]\+|#|g"
  </code></pre>
  
  <p>should output #abcd. And</p>
  
  <pre><code>echo abcd|sed "s|[0-9]\+|#|g"
  </code></pre>
  
  <p>should output abcd.</p>
  
  <p>But on OS X 10.4.11 the first expression outputs 1234abcd. Using * instead of + works for the first example but fails on the second, outputting #abcd, because the [0-9] pattern is matched zero times.</p>
  
  <p>Does the + operator not work in regular expressions in OS X? Is there an alternative?</p>
  
  <p>Thanks</p>