omni is a python script that let you check if a URL is UP or DOWN and if it is UP, it saves it in alive.txt. Another option of omni is that it can find all the possible subdomain, using subfinder, and than it will check each subdomain to see if it is reachable or not, if yes than it will save it in subdomains.txt
git clone https://github.com/SSHpectator/omni.git
cd omni
python3 alive.py