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In this guide, we'll be taking you through the step by step process of using Client URL or "cURL" with proxies.

What is cURL?

cURL is command-line based tool and library for transferring data to and from a server. This tool is widely used in networking and development to make requests to send or receive data. When using the cURL command it allows the user, through the command line, to specify and target a server URL. It is installed on almost all UNIX based operating systems. As a relatively quick script to run, it's a powerful tool to use to test your proxies; as well as any other tasks required.

There are many useful functions of cURL, such as:

• Downloading files from a website without the need to use a web browser.
• Checking the status of a web server, monitoring the response times.
• Quickly scraping web pages.

If you're already utilising cURL and are experiencing blocks, it's likely you're sending too many requests from the same IP address. In this case, we look to use proxies to navigate around that.

Getting Started

To start, you can use this to get the main page from a web server:   curl https://ipinfo.io   From this, you are initiating a GET request at the specified URL. It's worth noting, that URL is protocol dependant. When using cURL, if you fail to specify it will default to the most often used host name prefixes. In this case, it would be HTTPS.

Using cURL With Proxies

Sending the same request repeatedly, on the same IP, could result in that IP being restricted. In this instance, you'll be required to use a proxy to circumvent that restriction. For this you'll be using the inbuilt library.

To dictate a proxy, we use:   -x   or   --proxy   Similarly to Python requests, we will need to restructure the proxy from the format on the dashboard of IP:PORT:USER:PASS to USER:PASS@IP:PORT. Once done you'll be able to send the request at the site, using a proxy to change your IP as shown:   curl -x "USER:PASS@IP:PORT" https://ipinfo.io  

Troubleshooting

Error codes are easily used to troubleshoot.

Error 404 would indicate the page is not found. Check the target URL is formatted correctly.

Error 407 is a proxy authentication error. This means the proxy is unable to authenticate the client.

Error 400 is commonly given due to invalid syntax.

In conclusion cURL is a powerful and lightweight tool. It might seem intimidating at first, but with some practise it becomes a great addition to the networkers arsenal.