crawl a web page, extract all domains and resolve them to IP addresses with bash and common GNU/Linux tools

## crawl-extract-resolve.sh
#!/bin/bash

url='rawsec.ml'

domains=$(curl $url -s | grep -E 'https?://[^"]*' | cut -d '/' -f 3 | cut -d '"' -f 1 | uniq)

filename='/tmp/temporary_ips.txt'

for domain in $domains
do
  dig +noall +answer $domain | awk '/\sA\s/ {print $5}' >> $filename
done

cat $filename | sort -u