title: (( COUNT++ )) -> "COUNT++: not found" in shell script
body: <pre><code>#!/bin/sh
  INTERVAL=1
  COUNT=0
  while [ $COUNT -le 9 ]
  do
      (( COUNT++ ))
      sleep $INTERVAL
      echo "count is $COUNT"
  done
  </code></pre>
  
  <p>On execution.</p>
  
  <pre><code>$ sh ascript 
  ascript: 9: COUNT++: not found
  count is 0
  ascript: 9: COUNT++: not found
  count is 0
  ascript: 9: COUNT++: not found
  count is 0
  ascript: 9: COUNT++: not found
  count is 0
  ascript: 9: COUNT++: not found
  count is 0
  ascript: 9: COUNT++: not found
  count is 0
  ascript: 9: COUNT++: not found
  count is 0
  ascript: 9: COUNT++: not found
  </code></pre>