title: Sed error : bad option in substitution expression
body: <p>I have a configuration file (<code>gpsd.default</code>) containing data with the following format:</p>
  
  <pre><code># If you must specify a non-NMEA driver, uncomment and modify the next line     
  GPSD_SOCKET="/var/run/gpsd.sock"                                                
  GPSD_OPTIONS=""                                                                
  GPS_DEVICES="" 
  </code></pre>
  
  <p>I am making a change on the file with sed:</p>
  
  <pre><code>sed -i 's/^GPS_DEVICES="".*/GPS_DEVICES="dev/ttyUSB1"/' /etc/default/gpsd.default
  or 
  sed -i '4s/^.*/GPS_DEVICES="dev/ttyUSB1"/' /etc/default/gpsd.default
  </code></pre>
  
  <p>The above <code>sed</code> command returns error:</p>
  
  <blockquote>
    <p>sed: bad option in substitution expression</p>
  </blockquote>
  
  <p>Because the new line contains "<code>/</code>" in its expression.</p>
  
  <p>How to update my <code>sed</code> command to make it work?</p>