A little bash script to gather valid AND fast DNS Resolvers from public-dns.info

getValidDNS.sh

if [ "$#" -eq 0 ] || [ "$#" -gt 2 ] || [[ $* == *--help* ]] || [[ $* == *-h* ]]; then                                                                                                                              
    echo "Usage ./getValidDNS.sh [output file] [optional: timeout (seconds)]"                                                                                                                                      
    exit 1                                                                                                                                                                                                         
fi                                                                                                                                                                                                                 
                                                                                                                                                                                                                   
if [ "$#" -eq 2 ]; then                                                                                                                                                                                            
    timeout=$2                                                                                                                                                                                                     
else                                                                                                                                                                                                               
    timeout=1                                                                                                                                                                                                      
fi                                                                                                                                                                                                                 
                                                                                                                                                                                                                   
rm us.txt                                                                                                                                                                                                          
wget -q "https://public-dns.info/nameserver/us.txt"                                                                                                                                                                
for line in $(cat us.txt); do                                                                                                                                                                                      
    if [[ $line =~ .*:.* ]]; then                                                                                                                                                                                  
        continue                                                                                                                                                                                                   
    fi                                                                                                                                                                                                             
    result=$( dig +time=$timeout A localhost.rhynorater.com @$line )                                                                                                                                               
    if [[ $result =~ "127.0.0.1" ]]; then                                                                                                                                                                          
        echo "Valid: $line"                                                                                                                                                                                        
        echo $line >> $1                                                                                                                                                                                           
    else                                                                                                                                                                                                           
        echo "Invalid: $line"                                                                                                                                                                                      
    fi                                                                                                                                                                                                             
done