05-validint

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

validint()
{
  # Validate first field and test that value against min value $2 and/or 
  # max value $3 if they are supplied: If the value isn't within range or
  # it's not composed of just digits, fail.

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

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

  # Is the first character a '-' sign?
  if [ "${number%${number#?}}" = "-" ] ; then
    testvalue="${number#?}" # Grab all but the first character to test.
  else
    testvalue="$number"
  fi
  
  # Create a version of the number that has no digits, for testing.
  nodigits="$(echo $testvalue | sed 's/[[:digit:]]//g')"
  
  # Check for non-digit characters.
  if [ ! -z $nodigits ] ; then
    echo "Invalid number format! Only digits, no commas, spaces, etc" >&2
    return 1
  fi
  
  if [ ! -z $min ] ; then
    # Is the input less than the minimum value?
    if [ "$number" -lt "$min" ] ; then
      echo "$number is too small: smallest acceptable value is $min" >&2
      return 1
    fi
  fi
  if [ ! -z $max ] ; then
    # Is the input greater than the maximum value?
    if [ "$number" -gt "$max" ] ; then
      echo "Your value is too big: largest acceptable value is $max" >&2
      return 1
    fi
  fi
  return 0
}

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