Converter.sh, a bash script to convert domain lists to resolved IP lists without duplicates

converter.sh

#!/bin/bash
# Converter.sh by @xdavidhu
# This is a script inspired by the Bug Hunter's Methodology 3 by @Jhaddix
# With this script, you can convert domain lists to resolved IP lists without duplicates.
# Usage: ./converter.sh [domain-list-file] [output-file]

echo -e "[+] Converter.sh by @xdavidhu\n"
if [ -z "$1" ] || [ -z "$2" ]; then
  echo "[!] Usage: ./converter.sh [domain-list-file] [output-file]"
  exit 1
fi
echo "[+] Resolving domains to IPs..."
while read d || [[ -n $d ]]; do
  ip=$(dig +short $d|grep -oE "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b"|head -1)
  if [ -n "$ip" ]; then
    echo "[+] '$d' => $ip"
    echo $ip >> $2
  else
    echo "[!] '$d' => [RESOLVE ERROR]"
  fi
done < $1
echo -e "\n[+] Removing duplicates..."
sort $2 | uniq > $2.new
mv $2.new $2
echo -e "\n[+] Done, IPs saved to '$2'."

Hey inteligent.
Please create such repo with additional feature like specifying no. of threads, and taking resolvers from .txt file. which would increase the speed of resolve of domain to ip.

Thanks --> Does anyone have tips for recon for finding information disclosure Vulns? thanks