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====== SED - Change - Change lines in a file ======

This script will obtain the current IP address for different sites and update the /etc/hosts file with the correct IP address.

It could be run through Cron to ensure that the host file keeps an updated list of IPs.

----

===== Input file =====

Assuming /etc/hosts contains:

<file bash /etc/hosts>
1.2.3.4  restrict.youtube.com
1.2.3.4  restrictmoderate.youtube.com
1.2.3.4  strict.bing.com
1.2.3.4  forcesafesearch.google.com
1.2.3.4  safe.duckduckgo.com
</file>



----

===== Script using dig =====

<file bash update_hosts.sh>
#!/bin/bash

update_ip_address() {
file=/etc/hosts
if [[ $(grep $1 $file) ]]; then
	IP=$(dig +noall +answer +short @8.8.8.8 $1 | \
		grep -oE '((1?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])\.){3}((1?[0-9]?[0-9]|2[0-4][0-9]|25[0-5]))')
	sed -i "/$1/ s/.*/$IP\t$1/g" $file
fi
}

update_ip_address restrict.youtube.com
update_ip_address restrictmoderate.youtube.com
update_ip_address strict.bing.com
update_ip_address forcesafesearch.google.com
update_ip_address safe.duckduckgo.com
</file>

----

===== Script using nslookup =====

<file bash update_hosts.sh>
#!/bin/bash

update_ip_address() {
file=/etc/hosts
if [[ $(grep $1 $file) ]]; then
	IP=$(nslookup -query=A $1 8.8.8.8 | grep 'Address:' | tail -1 | \
		grep -oE '((1?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])\.){3}((1?[0-9]?[0-9]|2[0-4][0-9]|25[0-5]))')
	sed -i "/$1/ s/.*/$IP\t$1/g" $file
fi
}

update_ip_address restrict.youtube.com
update_ip_address restrictmoderate.youtube.com
update_ip_address strict.bing.com
update_ip_address forcesafesearch.google.com
update_ip_address safe.duckduckgo.com
</file>

----

===== Output File =====

The original input file will be changed to this:

<file bash /etc/hosts>
216.239.38.120  restrict.youtube.com
216.239.38.119  restrictmoderate.youtube.com
204.79.197.220  strict.bing.com
216.239.38.120  forcesafesearch.google.com
52.142.126.100  safe.duckduckgo.com
</file>