title: Sed script that matches lines containing a string but does not include another string
body: <p>I am trying to write a sed script that replaces a portion of a line but only on lines that do not have a "$" sign in it.  </p>
  
  <p>For example, the file may look like</p>
  
  <pre><code>host=$myvar
  param1=val1
  param2=val2
  host=abc
  host=def
  </code></pre>
  
  <p>I want to replace the "host=abc" and "host=def" with "host=zzzzz" and ignore the "host=$myvar".  So the final output should look like:</p>
  
  <pre><code>host=$myvar
  param1=val1
  param2=val2
  host=zzzzz
  host=zzzzz
  </code></pre>
  
  <p>I tried the a few regex expressions, but they didn't work.  </p>