title: Use Windows findstr to list files not containing a string
body: <p>From Windows CMD I can use </p>
  
  <pre><code>findstr -m subroutine *.f90
  </code></pre>
  
  <p>to list all files with suffix .f90 containing "subroutine". To list all .f90 files not containing the string I can do something like</p>
  
  <pre><code>dir /b *.f90 &gt; files.txt
  findstr -m subroutine *.f90 &gt; files_with_string.txt
  </code></pre>
  
  <p>and then write a script to list the lines in files.txt not found in files_with_string.txt. Is there a more elegant way?</p>