Do you mean blocking yahoo.com to the client PCs?
In squid proxy server add the entry in /etc/squid/squid.conf file as below
acl blocked_sites dstdomain "/etc/squid/.blocked_sites"
http_access deny blocked_sites
Now add the sites whichever you need in .blocked_sites file, the acl name, file path and file name can be anything as you wish. But make sure to change the entries in /etc/squid/squid.conf file according to your changes.
save the file and reload the squid service
service squid reload
It blocks not only elinks but also block other CLI & GUI browsers.