title: Why do alternate delimiters not work with sed -e '/pattern/s/a/b/'?
body: <p>Here is something I have discover that doesn't make sense.</p>
  
  <p>Output of <code>cat config.h</code>:</p>
  
  <pre><code>define somevar foo // Sample variable
  </code></pre>
  
  <p>This version of the command works to change foo to bar and preserve the comments:</p>
  
  <pre><code>sed -e '/somevar/s/foo/bar/' config.h
  </code></pre>
  
  <p>This doesn't work:</p>
  
  <pre><code>sed -e '|somevar|s|foo|bar|' config.h
  </code></pre>
  
  <p>Gives this error:</p>
  
  <blockquote>
    <p>sed: -e expression #1, char 1: unknown command: `|'</p>
  </blockquote>
  
  <p>Funnily enough this does work:</p>
  
  <pre><code>sed -e '/somevar/s|foo|bar|' config.h
  </code></pre>
  
  <p>Perhaps I am missing some part of the documentation. It seems very odd to have two different delimiters in the same sed command.</p>
  
  <p>Bug or feature?</p>