title: Sed for partial replacement?
body: <p>Imagine I have a file that has the following type of line:</p>
  
  <p>FIXED_DATA1 VARIABLE_DATA FIXED_DATA2</p>
  
  <p>I want to change the fixed data and leave the variable data as is. <em>For various reasons</em>, using two sed operations to replace the fixed data will not work. For instance, the fixed fields might be double-quotes, and the line has other areas containing them, thus really the regex is written to match a pattern in the variable data and the fixed data.</p>
  
  <p>If I'm bent on using sed, is there a way to change both fixed data fields at once while leaving the variable field unchanged?</p>
  
  <p>Thanks.</p>