Bash variable echoing 0

Question

I'm trying to create a simple bash script but I can't get the variable handling right. When the RESULT variable receives an empty value it does not echo "-1", it returns a 0. Why does bash turn the empty value into 0?

SERVICE="$1"
RESULT=`ps auxw | grep ${SERVICE} | grep -v grep | awk '{s+=$3} END {print s}'`
if [ -z "$RESULT" ]; then
   echo "-1"
else
   echo $RESULT
fi

Answer 1

Because there is always a ${RESULT}. You see, you put the ${SERVICE} in the command line when you search for it so its always found. See how can we avoid it:

cat search.sh

SERVICE="$1"
RESULT=$(ps auxw | grep ${SERVICE} | grep -v 'grep\|search.sh' | awk '{s+=$3} END {print s}')
if [ -z "$RESULT" ]; then
   echo "-1"
else
   echo $RESULT
fi

I added the name of the script into the grep -v. Otherwise there is always a process called search.sh ${SERVICE}

However it is far from best practice. As I understand, you need the current CPU usage of the process by name? Consider the following:

SERVICE="$1"
RESULT=`pgrep ${SERVICE}`
if [ -z "$RESULT" ]; then
   echo "-1"
else
   for proc in ${RESULT}; do ps -p ${proc} -o %cpu | tail -n +2; done
fi