Monitor top-10000 hosts from different places in the world. Give output of change.

alexamontor.sh

#!/bin/bash                                                                                                                                       

open_dns() {
    # Look for open DNS at X.X.Y.Y                                                                                                                
    parallel -j0 --tag host -t a youtube.com {1}.{1}.{2}.{2} ::: {1..255} ::: {1..255} |
        grep 'youtube.com has address' |
        perl -pe 's/^(\d+) (\d+)\t.*/$1.$1.$2.$2/'
}

if [ ! -e open_dns_list ] ; then
    # Create list of open DNS if it does not exist                                                                                                
    open_dns > open_dns_list
fi

if [ ! -e top-1m.csv.zip ] ; then
    # Download Alexa list if it does not exist                                                                                                    
    wget http://s3.amazonaws.com/alexa-static/top-1m.csv.zip
fi

# Unpack top-1m                                                                                                                                   
zcat top-1m.csv.zip |
    # Keep only top 10000                                                                                                                         
    head -n10000 |
    # Split list on ,                                                                                                                             
    # Retry lookups 10 times if they fail                                                                                                         
    # Sort output because the order is not significant                                                                                            
    # mispipe is needed to get the error code from host                                                                                           
    # look up 'a' and 'mx' record                                                                                                                 
    # on all open DNS servers                                                                                                                     
    # save output to new                                                                                                                          
    parallel -j0 -k --tagstring {3}-{1}-{4} --colsep , --retries 10 \
             mispipe \"host -t {1} {3} {4}\" sort \
             ::: a mx \
             :::: - \
             :::: open_dns_list > new;
# Is there any difference from last run?                                                                                                          
diff new old;
# Make this the basis for next run                                                                                                                
mv new old