Prints even numbers, and odd numbers

First script

#!/bin/bash
re='^-?[0-9]+([.][0-9]+)?$'
if ! [[ $2 =~ $re ]] ; then
  echo "El parámetro inicial NO es un número."
  exit
fi

if ! [[ $3 =~ $re ]] ; then
  echo "El parámetro final NO es un número."
  exit
fi

option=$1
begin=$2
((end=$3+1))

if [ $option == par ]; then
  while (($begin<$end)); do
    if (($begin%2==0));then 
      echo $begin
    fi
    let begin=begin+1
  done
elif [ $option == impar ]; then
  while (($begin<$end)); do
    if (($begin%2!=0)); then
       echo $begin
    fi
    let begin=begin+1
  done
fi

if [ $option == par ]; then
  while (($begin<$end)); do
    if (($begin%2==0));then 
      echo $begin
    fi
    let begin=begin+1
  done
elif [ $option == impar ]; then
  while (($begin<$end)); do
    if (($begin%2!=0)); then
       echo $begin
    fi
    let begin=begin+1
  done
fi