[OS] Passed OS Students

#!/bin/bash
#if there is not exactly 1 argument
if [ $# -ne 1 ]
then
    echo "USAGE: `basename $0` file_name.csv"
    exit 1
fi
#if the argument don't exist
if [ ! -f $1 ]
then
        echo "Ne postoi taa datoteka. Probaj pak!"
        exit 1
fi
FILENAME=`echo $1 | awk -F. '{print $1}'`
#if the output file exists, delete it, then create it again
if [ -f passed_${FILENAME}.csv ]
then
        rm passed_${FILENAME}.csv
fi
touch passed_${FILENAME}.csv
echo "Surname,\"First name\",Index,Points" >> passed_${FILENAME}.csv

SODRZINA=`cat $1 | grep [0-9] | awk -F, '$4>4 {print $0}'`
NUMBER_PASSED=`cat $1 | grep [0-9] | awk -F, '$4>4 {print $0}' | wc -l`
TOTAL_POINTS=0

for line in $SODRZINA
do
        POINTS=`echo $line | awk -F, '{print $4}'`
        TOTAL_POINTS=`expr $TOTAL_POINTS + $POINTS`
        echo $line >> passed_${FILENAME}.csv
done
AVERAGE=`expr $TOTAL_POINTS / $NUMBER_PASSED`
echo "Average points of passed students is: ${AVERAGE}!" >> passed_${FILENAME}.csv
cat passed_${FILENAME}.csv