An Introduction to cURL: The Most Popular HTTP Client

Hold on to your keyboards, web developers! If your toolkit doesn't feature cURL, you might be missing out on one of the most powerful tools in the game. cURL isn’t just a CLI-based HTTP client—it's the command-line HTTP client!

Join us on a journey into the heart of cURL, where we’ll uncover its mysteries, explore its capabilities, and equip you with the knowledge to use it like a pro. Ready to unleash the true power of cURL? Let's roll!

What Is cURL?

cURL, short for “Client for URLs,” is a software project encompassing a command-line tool and a library called libcurl. This duo specializes in data transfer with URL syntax across a spectrum of network protocols. libcurl also boasts features like SSL support, proxy tunneling, header configuration, and cookie management.

Delving into the complete list of protocols supported by libcurl feels like navigating a digital alphabet soup. That includes HTTP, HTTPS, FTP, SFTP, IMAP, POP3, SMTP, MQTT, and dozens of others. The list is so long that you may have never even heard of some of them—rest assured, you're not alone if that's the case! 😜

Why has cURL achieved rock star status among developers? It's all about its cross-platform prowess! With libcurl bindings available in so many programming languages—think PHP, Python, and Java—cURL seamlessly integrates into diverse tech stacks. The popularity lies in its ubiquity. cURL is pre-installed on Linux, macOS, and Windows, making it the go-to tool for web requests in the terminal on any machine straight out of the box.

Whether retrieving web content, testing APIs, or uploading files, cURL stands tall as an essential tool in the toolkit of any web developer. Nothing can match its unparalleled flexibility and efficiency. 🚀

cURL in Action: Syntax and Examples

So, you’ve got cURL in your toolkit, but how to use it? Simple! Launch a command in your terminal following this syntax:

curl [options] [URL]

URL is the destination—the online server or resource you're targeting, while some common cURL options are:

• -X or --request: To set the HTTP method to use.

• -d or --data: To add data in the body of your request.

• -b or --cookie: To manage cookies for your requests.

• -H or --header: To add a custom header to your requests. For multiple headers, repeat the options many times. GET by default.

• -v or --verbose: To print detailed information for debugging.

  
  

To find out all the options available, check out the docs 🔎

⚠️ Note 1: Beware, command-line curl options sensitive. Thus, -x and -X have two different meanings.

⚠️ Note 2: In PowerShell, curl is an alias for Invoke-Request. To use cURL on Windows, write curl.exe instead of curl.

Now, get ready to see the cURL syntax in action in real-world examples categorized by HTTP methods!

GET

Here’s how to use cURL to get the source HTML of a target web page:

curl "https://example.com/"

Under the hood, cURL will make a GET request, fetch the HTML document associated with the https://example.com/ web page, and print it in the terminal.

You just retrieved information with a single command. Impressing, isn't it? 🔥

POST

The cURL POST example below calls the https://api.example.com/users endpoint with the JSON data required to create a new user:

curl -X POST -H "Content-Type: application/json" -d '{"name": "John", "age": 30}' "https://api.example.com/users"

Notice the -X option to specify the desired HTTP method. Pay also attention to the use of the -H option, which sets the Content-Type header, and the -d option, specifying the raw JSON data in a string. Check out a dedicated cURL POST request guide!

PUT

cURL PUT calls adhere to the following syntax:

curl -X PUT -d "name=Amazon%20Scraping&description=Automated%20data%20extraction%20for%20retrieving%20price%20data&status=completed" "https://api.example.com/projects/12"

The HTTP request will update the project with ID 12 using the provided data. In this example, the data in the request body is in the application/x-www-form-urlencoded format, in contrast to the JSON body used in the cURL POST call above. This flexibility in data formats showcases the adaptability of cURL for different use cases.

PATCH

Want to perform a PUT request in cURL to update a single field of an online resource? Here’s how you can do it:

curl -X PATCH -d "status=failed" "https://api.example.com/projects/12"

DELETE

cURL allows you to make DELETE request and erase the existence of existing entities, as below:

curl -X DELETE https://api.example.com/user/431

After this API call, the user with ID 431 will no longer exist!

Advanced cURL Options

cURL offers a multitude of options, each offering a unique capability for complex use cases. As you navigate through that universe, certain advanced options stand out. Here are the top 10 most useful advanced cURL options:

• -o or --output: To write the output to the specified local file instead of <stdoud>.
• -O or --remote-name: To save the output to a remote file.
• -i or --include: To include the response HTTP headers in the output.
• -u or --user: To authenticate with a username and password in the user:password format.
• -L or --location: To follow the redirects when the server responds with a 3XX response code.
• -e or --referer: To send the “Referrer Page” information to the HTTP server.
• -x or --proxy: To specify the URL of the proxy server to make the request through. For more information, read our tutorial on how to use cURL with a proxy or watch the video below.
• --rate: To specify the maximum transfer frequency you want cURL to respect to avoid triggering rate-limiting measures.
• --data-binary: To send data to the server exactly as specified with no extra processing whatsoever.
• --compressed: To request a compressed response and automatically decompress the response content.

Mastering these options empowers you to wield cURL with unparalleled finesse in the ever-evolving realm of web interactions. 🌐

How to Get the Most Out of cURL

cURL is a powerhouse for web requests, but its default setup leaves it vulnerable to anti-bot measures. Consider, for example, its default User-Agent header:

curl/X.Y.Z

See how to change cURL user agent value.

Now, compare that with the latest Chrome's user agent:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

That’s a quite different string!

Using cURL without overriding that header is just like screaming to the target server, “Look at me! I’m an automated, non-browser, robot request!”

No wonder, that may trigger defensive mechanisms 😅. Also, don’t forget that cURL is just an HTTP client. Thus, it can’t deal with pages relying on JavaScript for rendering or data retrieval.

👎That’s bad if you want to use cURL for web scraping!👎

Should you stop using cURL, then? Not at all! You just need to equip it with the right tools! To unlock cURL's full potential and address its limitations, either integrate it with a:

• Web proxy: To get a fresh, geolocated, trustworthy IP at each request; or a
• Web unlocking tool: To access public statics or JavaScript-dependent web pages while also bypassing bot detection technologies.

Whatever your decision, Bright Data has you covered! With one of the largest and most reliable proxy networks in the market, Bight Data has millions of proxy servers spread all over the world. Plus, its Web Unlocker solution enables you to access any public website via cURL, regardless of its level of bot protection.

Conclusion

cURL, the rock star of HTTP clients, is the go-to tool for developers making web requests in the terminal. Here, you've now mastered its usage with common HTTP methods and explored its diverse options. That’s a powerful tool, but let's be real—most sites will be able to detect that you’re contacting them via cURL.

Fear not! The antidote is simple: enlist the help of a web proxy or, for optimal results, embrace the Web Unlocker solution from Bright Data. Join us in our mission to democratize the Internet, making it accessible to everyone, everywhere—even through the mighty cURL!

Until next time, keep exploring the Web with freedom!