Shell script read user input

Question

I got stuck on this shell script code where it requires user to enter the group number and find the largest and the average out of that group number. My code ATM only works with passing the group number as a command-line argument. How to prompt for the group number as user input?

read n

    if [ $n -ge 1 ]; then

    sum=0

     count=$n

     max=-1000
    if [ $max -lt $1 ]; then

    max=$1

    fi

    while [ $n -ge 1 ]; do

            case $1 in
            [0-9] | [1-9][0-9])
            sum=`expr $sum +$1`;;
            -[1-9] | -[1-9][0-9])
            sum=`expr $sum + $1`;;


    done

    if [ $count -gt 0 ]; then

    avg=`expr $sum / $count`

    echo The largest number is $max

    echo The average number is $avg

Answer 1

From your comments it seems you would like to read values from stdin rather than from the command line. To do that in Bash you use the read builtin:

read -ep "Enter group number: " group
printf "Entered %d\n" $group

For interactive prompting it is usually put in the test part of a while loop where you can break if the input is invalid:

shopt -s extglob
while read -ep "Enter group number: " group; do
    case $group in 
        ?(-)+([0-9]))    # valid input
            # compute average here
        *) break ;;      # not valid input
    esac
done

See help read for more information.

Answer 2

You're working way too hard, and your script is way too verbose. Try:

#!/bin/sh

test $# -gt 0 || { echo Please enter at least one argument >&2; exit 1; }
max=0
for x; do
  test "$max" -lt $x && max=$x
  test $? -gt 1 && exit 1
  : $(( count += 1 ))
  : $(( sum +=  x ))
done

echo max = $max
printf "avg = "
expr $sum / $count

Since you used expr in your script, I'm doing the same, but be aware that all of the arithmetic will be done in the integers (so the reported average will be the greatest integer less than the actual average, and non-integer input will be considered an error). This solution relies on test returning a value greater than 1 when it encounters an error (eg, non integer input), which is the behavior specified by the open group.

Also note that this puts the error message on stderr (where error messages belong) and returns a non-zero value to indicate that the script failed.