#!/bin/bash

[[ -z "${1}" ]] && netstat -punta && exit 0

ISDIGIT="false"
REGEX="^[[:digit:]]+$"
[[ "${1}" =~ ${REGEX} ]] && netstat -punta | grep ":${1}" && exit 0
[[ "${1}" =~ ${REGEX} ]] && netstat -punta | grep "${1}"
exit 0