title: confirm numeric character of variable
body: <p>I need to do an operation but something is wrong in my code in bash</p>
  
  <p>I have 4 variables,  km1, km2, km3, km4.</p>
  
  <p>I want to sum the 4 variables except when the value is "CLOSED"</p>
  
  <pre><code>3.200
  CLOSED
  1.800
  0.600
  </code></pre>
  
  <p>When I do the following sum, there is an error...I thing my variables are not numeric, any help? How can I force them to be numeric and then do the sum?</p>
  
  <pre><code>let km=$km1+$km3+$km4
  echo $km
  </code></pre>
  
  <p>./sum.sh: line 41: let: km=3.200: syntax error: invalid arithmetic operator (error token is ".200")</p>