cURL is used to transfer data in the command line or script. From cars to mobile devices, it is needed everywhere. It can send and receive data through various network protocols (such as HTTP, HTTPS, FTP, etc.).

Many people don’t know what cURL is and how to use it. This article will introduce the basic concepts of cURL, common usage, and its application scenarios in actual operations.

How cURL works

The main function of cURL is to send a request to a URL and receive the response returned by the server. In short, cURL is like a virtual "browser" that is only responsible for sending requests and getting the corresponding data.

For example, when you enter a web page address in the browser and press Enter, the browser actually sends an HTTP request to the server, and then the server responds to the request and returns the web page content to the browser for display. cURL can also do this, but it will not display the web page, but directly output the received data in the command line or save it to a file.

Install cURL

Most modern operating systems (including Linux, macOS, and Windows) come with cURL pre-installed. If it is not installed, users can install it in the following ways:

On Linux (Ubuntu as an example):

On macOS (using Homebrew):

On Windows:

You can download the corresponding binary file from the official website of cURL (https://curl.se/) and add it to the system's environment variables.

How to use cURL?

cURL sends requests through a proxy

cURL supports sending requests through a proxy server. Just use the -x or --proxy option to specify the address and port of the proxy server. cURL supports multiple types of proxies, including HTTP, HTTPS, and SOCKS proxies.

1. HTTP proxy

Suppose you want to send a request through an HTTP proxy server, you can use the following command:

In this command:

http://proxy.example.com:8080 is the address and port of the proxy server.

https://www.example.comis the target website.

This will first send the request to the proxy.example.com proxy server, and then the proxy server will forward the request to the target website.

2. HTTPS proxy

If you want to send requests through an HTTPS proxy, the command format is similar to that of an HTTP proxy, except that you only need to specify the protocol part of the proxy as https:

This command will use an HTTPS proxy server to send requests to increase the security of the transmission.

3. SOCKS proxy

In addition to HTTP and HTTPS proxies, cURL also supports SOCKS proxies. SOCKS proxies are more flexible than HTTP proxies and support more protocols and data streams. The commonly used SOCKS versions are SOCKS4 and SOCKS5. The following is the command to send a request through a SOCKS5 proxy:

In this command, socks5://proxy.example.com:1080 means to use a SOCKS5 proxy to send the request.

4. Proxy with authentication

Some proxy servers require authentication. If your proxy server requires a username and password, you can include this information in the proxy address:

This method allows you to authenticate through an HTTP or SOCKS proxy using the specified username and password.

Follow redirects

In a network request, the server sometimes returns a redirect response to inform the client that the resource has been moved to another URL. Typically, redirect responses have an HTTP status code of 301 (permanent redirect) or 302 (temporary redirect). By default, cURL does not automatically follow redirects, but you can enable this feature with the -L option.

To enable redirect following, you just need to add the -L option to your request. For example:

In this command, cURL will automatically follow the server's redirect request until it gets the final response.

Simulate browser behavior

Sometimes, websites will determine whether a request is from a browser or a script based on the request's User-Agent. With cURL's -H option, you can simulate the behavior of various browsers to avoid being blocked:

This way, the website will think that the request is from a normal browser, not a script.

Dealing with anti-crawler mechanisms

Some websites may deploy anti-crawler mechanisms such as IP blocking, request rate limiting, or verification codes to prevent malicious crawling of data. To avoid these problems, you can use cURL in conjunction with a proxy server to send requests to bypass some of these restrictions:

Other anti-crawler countermeasures

Reduce the request frequency: Add delays between multiple requests to simulate normal user behavior.

Randomize request headers: Randomly change the User-Agent and other header information for each request to increase diversity.

Summary

cURL is a powerful network tool that allows you to interact with servers. Combined with proxy servers and the ability to follow redirects, cURL becomes even more flexible and useful.

For more in-depth information on other interesting topics, such as How to Find the Best Unblocked YouTube Sites with a Proxy (https://www.piaproxy.com/blog/youtube-proxy/how-to-find-the-best-unblocked-youtube-sites-with-a-Proxy.html), How to Easily Find and Understand "My IP Location" (https://www.piaproxy.com/blog/ip-look-up/how-to-easily-find-and-understand-my-ip-location.html), etc., please visit PIAProxy's (https://www.piaproxy.com/blog/) blog, there are many interesting blog posts waiting for you to explore!