title: Why does sed command contain at symbols
body: <p>I don't understand why the following sed command contains an @ symbol:</p>
  
  <pre><code>sed 's@session\s*required\s*pam_loginuid.so@session optional pam_loginuid.so@g' -i /etc/pam.d/sshd
  </code></pre>
  
  <p>I've looked at /etc/pam.d/sshd for the before/after effects of this command:</p>
  
  <p>BEFORE:</p>
  
  <pre><code>...
  # Set the loginuid process attribute.
  session    required     pam_loginuid.so
  ...
  </code></pre>
  
  <p>AFTER:</p>
  
  <pre><code>...
  # Set the loginuid process attribute.
  session optional pam_loginuid.so
  ....
  </code></pre>
  
  <p>Is the @ symbol possibly part of regex or sed syntax?
  Could not find any doco on this.</p>
  
  <p>Note: The above sed command is actually part of a Dockerfile RUN command in tutorial:
  <a href="https://docs.docker.com/examples/running_ssh_service/" rel="noreferrer">https://docs.docker.com/examples/running_ssh_service/</a></p>