Write a daemon under linux

#! /bin/sh
#Process name can be modified shipInfo
PRO_NAME=shipInfo
WLAN=ra0
  
while true; do
  
# Use ps to get the number of $PRO_NAME processes
  NUM=`ps aux | grep ${PRO_NAME} | grep -v grep |wc -l `
# echo $NUM
# Less than 1, restart the process
  if ["${NUM}" -lt "1" ]; then
    echo "${PRO_NAME} was killed"
 ./shipInfo
# ${PRO_NAME} -i ${WLAN }
# Greater than 1, kill all processes, restart
  elif ["${NUM}" -gt "1" ];then
    echo "more than 1 ${PRO_NAME},killall ${PRO_NAME}"
    killall -9 $PRO_NAME
    ${ PRO_NAME} -i ${WLAN}
  fi
# kill the zombie process
  NUM_STAT=`ps aux | grep ${PRO_NAME} | grep T | grep -v grep | wc -l`
  
  if ["${NUM_STAT}" -gt "0" ];then
    killall -9 ${PRO_NAME}
    ${PRO_NAME} -i ${WLAN}
  fi
done
  
exit 0