#!/bin/bash
# isprime - given a number, ascertain if it's a prime or not
#     This uses what's know as trial division: simply check to see if any
#     number from 2 .. (n-1) divides into the number without a remainder.

  setglobal counter = '2'
setglobal remainder = '1'

if test $Argc -eq 0  {
  echo "Usage: isprime NUMBER" > !2
  exit 1
}

setglobal number = $1

# 3 and 2 are primes, 1 is not.

if test $number -lt 2  {
  echo "No, $number is not a prime" ; exit 0
}

# now let's run some calculations

while [ $counter -le $(expr $number / 2) -a $remainder -ne 0 ]
{
  setglobal remainder = $[expr $number % $counter]  # '/' is divide, '%' is remainder
  # echo "  for counter $counter, remainder = $remainder"
  setglobal counter = $[expr $counter + 1]
}

if test $remainder -eq 0  {
  echo "No, $number is not a prime"
} else {
  echo "Yes, $number is a prime"
}
exit 0