#!/bin/sh
# validint -- Validates integer input, allowing negative ints too.

function validint
{
 # Validate first field. Then test against min value $2 and/or
 # max value $3 if they are supplied. If they are not supplied, skip these tests.

 number="$1";   min="$2";   max="$3"

 if [ -z $number ] ; then
  echo "You didn't enter anything. Unacceptable." >&2 ; return 1
 fi

 if [ "${number%${number#?}}" = "-" ] ; then # is first char a '-' sign?
testvalue="${number#?}"   # all but first character
 else
  testvalue="$number"
 fi

 nodigits="$(echo $testvalue | sed 's/[[:digit:]]//g')"

 if [ ! -z $nodigits ] ; then
  echo "Invalid number format! Only digits, no commas, spaces, etc." >&2
  return 1
 fi

 if [ ! -z $min ] ; then
  if [ "$number" -lt "$min" ] ; then
    echo "Your value is too small: smallest acceptable value is $min" >&2
    return 1
  fi
 fi
 if [ ! -z $max ] ; then
   if [ "$number" -gt "$max" ] ; then
    echo "Your value is too big: largest acceptable value is $max" >&2
    return 1
   fi
 fi
 return 0
}


if validint "$1" "$2" "$3" ; then
 echo "That input is a valid integer value within your constraints"
fi