I am facing trouble just with modify_record function in the code provided below. I could use awk but my instructor told us to do it using sed. Could anyone help in this?

menu() {
    echo "choose one of the following options: n"
    echo "1) create a student database"
    echo "2) view a student database"
    echo "3) insert a student record"
    echo "4) delete a student record"
    echo "5) modify a record"
    echo "6) display result"
    echo ""
}


create_db() {
    echo "creating a student database..."
    touch student.db
    echo "created a student database."
}


view_db() {
    echo -e "opening database... n"
    cat student.db
}

insert_record() {
    echo -e "enter roll number: c"
    read roll
    echo -e "enter name of student: c"
    read name
    echo -e "enter marks of subject 1: c"
    read sub1
    echo -e "enter marks of subject 2: c"
    read sub2
    echo -e "enter marks of subject 3: c"
    read sub3
    
    echo "$roll|$name|$sub1|$sub2|$sub3" >> student.db
    
}

delete_record() {
    echo -e "enter roll number whose info is to be deleted: c"
    read roll
    grep -iv $roll student.db > temp.db && mv temp.db student.db
}

modify_record() {
    echo -e "enter roll no. whose info is to be modified: c"
    read roll
    #echo -e "enter name: "
    #read temp_name
    echo -e "enter sub1 marks: c"
    read newsub1
    echo -e "enter sub2 marks: c"
    read newsub2
    echo -e "enter sub3 marks: c"
    read newsub3

    sed -i "s/^$roll|([^|]*)|[^|]*|[^|]*||[^|]*$/&1|$newsub1|2|$newsub2|3|$newsub3/" student.db

 
    
}

calc_avg() {
    echo "enter roll no. whose average is to be calculated: c"
    read rollno
    x=`grep $rollno student.db | cut -d'|' -f3`

    y=`grep $rollno student.db | cut -d'|' -f4`
    
    z=`grep $rollno student.db | cut -d'|' -f5`
    
    sum=`expr $x + $y + $z`
    average=`expr $sum / 3`
    # echo -e "average: $averagen"
    echo -e "average: $averagen"
}


while : 
do
    menu
    read -p "enter your choice: " choice
    
    case $choice in
    1) create_db ;;
    2) view_db ;;
    3) insert_record ;;
    4) delete_record ;;
    5) modify_record ;;
    6) calc_avg ;;
    7) break ;;
    *) echo "invalid choice"
    esac
    
done

The database which is created when you run this code looks like this:

rollno|name|sub1|sub2|sub3

The sed line in modify_record(), rather than replacing the subject marks it inserts them randomly in between other fields. I looked up other solutions and tried to copy their implementation but it didn’t work.