Much *nix software will obey the proxy environment variables:
for a squid proxy on IP 220.127.116.11, for instance. (Use "unset" to turn these environment variables off later.) You can then test with and without the proxy thusly, for example:
w3m -no-proxy http://google.com/
Or you can test directly with telnet:
telnet 18.104.22.168 3128
which in the case of squid will result in following output:
Escape character is '^]'.
And then enter the URL you wish to access over the proxy:
GET http://www.google.com/ HTTP/1.1
followed by this line:
followed by two returns, and the site html will be dumped in your terminal.