Check port 25 opened.

check-port.sh

#!/bin/bash

file='list.txt'
port='25'

while getopts "p:f:" arg; 
do
	case $arg in
	p)
  		port=$OPTARG
  	;;
  	f)
  		file=$OPTARG
  	;;
	*)
  		echo "Unknown parameter."
  	;;
	esac
done

if [ -f $file ]
then
	if [ -z $port ]
		then
			cat $file | sort -u | while read -r ip; do nc -vz -w 3 $ip 25 >> /tmp/25-result.txt 2>&1; done
		else
			cat $file | sort -u | while read -r ip; do nc -vz -w 3 $ip $port >> /tmp/25-result.txt 2>&1; done
		fi
		echo "---Port $port opened:---"
		cat /tmp/25-result.txt | grep -w 'succeeded' | grep -oE "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b" | sort -ur
		rm -rf /tmp/25-result.txt
else
	echo -e "$file: File not found.\nUsage: $0 -p <Port Number|Default: 25> -f <File-IP-Listing>\nExample: $0 -p 80 -f list1.txt"
fi