title: Identify operating system
body: <p>My Fortran 90 code on Intel compiler depends on the operating system it is running on, e.g. </p>
  
  <pre><code>if (OS=="win7") then
     do X
  else if (OS=="linux") then
     do y
  end if
  </code></pre>
  
  <p>How do I do this programmatically?</p>