title: Join lines depending on the line beginning
body: <p>I have a file that, occasionally, has split lines. The split is signaled by the fact that the line starts with a space, empty line or a nonnumeric character. E.g.</p>
  
  <pre><code>40403813|7|Failed|No such file or directory|1
  40403816|7|Hi,
   The Conversion System could not be reached.|No such file or directory||1
  40403818|7|Failed|No such file or directory|1
  ...
  </code></pre>
  
  <p>I'd like join the split line back with the previous line (as mentioned below):</p>
  
  <pre><code>40403813|7|Failed|No such file or directory|1
  40403816|7|Hi, The Conversion System could not be reached.|No such file or directory||1
  40403818|7|Failed|No such file or directory|1
  ...
  </code></pre>
  
  <p>using a Unix command like sed/awk. I'm not clear how to join a line with the preceeding one.</p>
  
  <p>Any suggestion?</p>