Validation using While and IF

UNIX for Beginners Q & A
1

I am learning Shell scripting on own. I am trying to do an assignment to get details from the user like username their individual marks ,DOB and send a report in mail with the Details calculated like total and average.

validate_marks() {
  local Value=$1
  if [ "${Value}" -ge "0" ] && [ "${Value}" -le "100" ]
  then
  return 0
  else
  echo "Enter numbers between 0-100"
  exit 1.
  fi

  }
  echo "Enter Marks for each subject:"
    read -p "Enter English Marks:" ENG
      validate_marks $ENG
    read -p "Enter Maths Marks:" MATHS
      validate_marks $MATHS
    read -p "Enter Science Marks:" SCI
      validate_marks $SCI
    read -p "Enter History Marks:" HIST
      validate_marks $HIST
    read -p "Enter your Email id:" EMAIL
      validate_email $EMAIL

In the validate marks function I am checking if the value entered is between 0 -100 if it is more return error and go back to prompt until it is correct. How do I achieve this

2

First, replace the exit 1 by return 1 .
Then loop around the input until it's okay.

until
  read ... &&
  validate ...
do
  :
done

Here it checks the exit status of the read and the validate. If not 0(=okay) it runs the empty loop body and repeats.
The : (noop) satisfies the syntax.