# slow version
host="google.com"
port_list=(21 22 23 25 80 443 445 3389 5985 5986 8080 8443)
for port in ${port_list[@]}; do timeout 1 bash -c "echo >/dev/tcp/$host/$port" 2>/dev/null && echo "port $port is open" || echo "port $port is closed" done

# ram go burrrrr
host="google.com"
for port in {1..65535}; do timeout 1 bash -c "echo >/dev/tcp/$host/$port" 2>/dev/null && echo "port $port is open" || echo "port $port is closed" >/dev/null & done 2>/dev/null