How to Hide Your IP with Proxy Servers Using Linux curl

Proxy Server Types

Proxy servers sit between a browser and an HTTP server, forwarding requests. The main supported protocols are HTTP(S) and SOCKS. HTTP proxies are divided into three categories: transparent (the server sees the original IP), anonymous (the server knows a proxy is used but not the original IP), and high‑anonymous (the server cannot detect a proxy). SOCKS proxies include SOCKS4, SOCKS4A, and SOCKS5, which support TCP, UDP, server‑side DNS resolution, multiple authentication methods, and IPv6.

curl Proxy Options on Linux

The curl command can set proxies using -x host:port or --proxy protocol://[user:pwd@]host[:port]. Supported protocols are http_proxy, HTTPS_PROXY, socks4, socks4a, and socks5. Authentication methods can be specified with flags such as --proxy-basic, --proxy-ntlm, --proxy-negotiate, and --proxy-anyauth. Username and password can be provided via -U user:password or --proxy-user user:password.

Example: Setting an HTTP Proxy

curl -x 113.185.19.192:80 http://example.com/test.php

curl --proxy 113.185.19.192:80 http://example.com/test.php

curl -x http_proxy://user:[email protected]:80 http://example.com/test.php

Example: Setting a SOCKS5 Proxy

curl --socks5 122.192.32.76:7280 http://example.com/test.php

curl -x socks5://user:[email protected]:7280 http://example.com/test.php

Testing Proxy Anonymity

Create a test.php file that outputs selected $_SERVER variables. Example PHP code:

<?php
$array = array(
    'HTTP_USER_AGENT',
    'HTTP_HOST',
    'HTTP_ACCEPT',
    'PATH',
    'SERVER_SIGNATURE',
    'SERVER_SOFTWARE',
    'SERVER_NAME',
    'SERVER_ADDR',
    'SERVER_PORT',
    'DOCUMENT_ROOT',
    'SERVER_ADMIN',
    'SCRIPT_FILENAME',
    'REMOTE_PORT',
    'GATEWAY_INTERFACE',
    'SERVER_PROTOCOL',
    'REQUEST_METHOD',
    'QUERY_STRING',
    'REQUEST_URI',
    'SCRIPT_NAME',
    'REQUEST_TIME',
    'PHP_SELF'
);
$srv = $_SERVER;
foreach ($array as $name) {
    unset($srv[$name]);
}
print_r($srv);
?>

Access the script without a proxy, with a transparent proxy, an anonymous proxy, a high‑anonymous proxy, and a SOCKS5 proxy. Observe the output:

Without proxy: REMOTE_ADDR shows the client’s real IP.

Transparent proxy: REMOTE_ADDR shows the proxy IP, and headers like HTTP_X_FORWARDED_FOR and HTTP_VIA reveal the original IP and proxy usage.

Anonymous proxy: REMOTE_ADDR shows the proxy IP, but no original IP header; the presence of HTTP_PROXY_CONNECTION indicates proxy usage.

High‑anonymous proxy: Only REMOTE_ADDR shows the proxy IP; no additional headers expose proxy usage.

SOCKS5 proxy: Similar to high‑anonymous behavior, showing only the proxy IP.

These results help determine the anonymity level of each proxy type.