number_of_variables.sh

#!/bin/bash

read -p "Enter the number of variables: " number

regex='^[0-9]+$'

if [[ ! $number =~ $regex ]] ; then
   echo "Number should be integer"
   exit 1
fi

i=0
field=()

for x in {a..z}
do
     read -p "Var $x:   " -r 'field[i]'
     regex='^[0-9]+([.][0-9]+)?$'
     if [[ ! ${field[$i]} =~ $regex ]] ; then
        echo "Variable should be integer or float"
        exit 1
     fi
     i=$(($i+1))
     if [ $i -ge $number ]; then
         break
     fi
done

read -p "Enter the formula: " formula

i=0
for x in {a..z}
do
    formula=$(echo $formula | sed -e 's/'$x'/'${field[$i]}'/g')
    i=$(($i+1))
done

ans=$(echo $formula | bc);
if ! [ -z $ans ] ; then
    echo "Answer:  $ans"
fi