Shell script to verify connectable Google IPs

verify_google_ips.sh

#!/bin/bash

if [ $# -ne 1 ]; then
  echo "Usage: $0 <IP>[/subnet]"
  exit 1
fi

for ip in $(nmap -sL $1 | awk '/Nmap scan report/{print $NF}'); do {
  ip=$(echo $ip | tr -d '()')
  output=$(curl --connect-to :443:$ip:443 --connect-timeout 5 --verbose --head https://www.google.com.hk 2>&1)
  if [[ $output == *"HTTP/2 404"* ]]; then
    echo "$ip: HTTP 404"
  elif [[ $output == *"no alternative certificate subject name"* ]]; then
    echo "$ip: Certificate error - $(echo $output | grep -o 'subject: CN=[^\n]*' | cut -d' ' -f2)"
  elif [[ $output == *"HTTP/2 200"* ]]; then
    echo "$ip: Success"
  elif [[ $output != *"curl: (28)"* ]]; then
    echo "$ip: Failed - $(echo $output | grep -o 'curl: (.*) [^$]*$')"
  fi
} &
done