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Web scraping is an incredibly useful technique that allows you to extract data from websites. While there are many tools and libraries available for web scraping, one of the most versatile is a command-line utility called cURL.

In this in-depth guide, we‘ll explore what cURL is, why it‘s so popular for web scraping, and how you can start using it to collect data from the web. Whether you‘re a beginner looking to learn the basics or an experienced developer wanting to up your web scraping game, this article will provide all the details you need to know.

What is cURL?

cURL, which stands for "Client URL", is a command-line tool for transferring data using various network protocols. Originally released in 1997, cURL has become one of the most widely used utilities for interacting with web servers.

At its core, cURL allows you to make HTTP requests and receive responses, making it perfect for fetching the HTML source of web pages – the foundation of web scraping. But cURL‘s capabilities go far beyond simple page downloads. With support for over 25 different protocols including FTP, SMTP, and SSL, cURL is an incredibly flexible tool for all kinds of data transfer tasks.

Some common use cases for cURL include:

• Downloading the source code of web pages
• Submitting web forms and handling cookies/sessions
• Uploading files to web servers
• Testing APIs and inspecting HTTP headers
• Automating interactions with websites and web apps

cURL is free, open source, and available on just about every operating system and device, from Linux and macOS to Windows, Android and iOS. This ubiquity, combined with its power and flexibility, has made cURL the go-to utility for automating interactions with web servers.

Installing cURL

Before you can start using cURL for web scraping, you need to make sure it‘s installed on your system. The good news is that cURL comes pre-installed on most Unix-like operating systems, including Linux and macOS.

To check if you already have cURL, open up a terminal and type:


curl --version


If cURL is installed, this will display the version number and build info. If you get a "command not found" error, you‘ll need to install cURL yourself.

On Ubuntu and Debian Linux, you can install cURL with apt-get:


sudo apt-get install curl


On CentOS and Fedora, use yum:


sudo yum install curl


On macOS, the easiest way is to use Homebrew:


brew install curl


If you‘re on Windows, you have a few options. Recent versions of Windows 10 and 11 actually come with cURL pre-installed. But if you‘re on an older version, you can either install an official cURL build, use a package manager like Chocolatey, or install the Windows Subsystem for Linux which will give you access to the same cURL as on native Linux.

Using cURL – The Basics

Once you‘ve got cURL installed, you‘re ready to start using it for web scraping. Let‘s begin by looking at the basic syntax.

To download the HTML source of a web page, the most common cURL command is:


curl https://example.com


This will fetch the contents of the specified URL (in this case, http://example.com) and output it directly in your terminal.

If you want to save the HTML to a file instead of printing it to the screen, use the -o flag followed by a filename:


curl -o example.html https://example.com


This will save the page source to a file called example.html in the current directory.

If you want the saved file to have the same name as the remote file, use -O instead:


curl -O https://example.com/page.html


This will create a local file called page.html with the contents of https://example.com/page.html.

Those are the basics, but cURL has dozens of different options you can use to customize its behavior. Some of the most useful ones for web scraping include:

• -L to follow redirects
• -H to set custom HTTP headers
• –cookie to send cookies
• –data to submit form data or JSON payloads
• –user-agent to set the user agent string

We‘ll look at some of these more advanced options later on. But first, let‘s talk about some of the benefits of using cURL for web scraping.

Why cURL is Great for Web Scraping

So what makes cURL such a popular choice for web scraping compared to other tools and libraries? There are a few key reasons:

1. cURL is extremely versatile and feature-rich. With support for cookies, redirects, proxies, authentication, and dozens of protocols, cURL can handle just about any web scraping scenario you might encounter. You‘d be hard pressed to find a website that cURL can‘t scrape.

2. cURL is lightweight and fast. As a command-line utility written in C, cURL has very little overhead compared to web scraping frameworks and libraries. This makes it an excellent choice when you need to scrape a large number of pages quickly.

3. cURL requires no dependencies. Unlike language-specific libraries that depend on particular modules, runtimes, and package managers, cURL is completely standalone. All you need is the cURL binary which is available everywhere.

4. cURL is great for automation. Need to set up a cron job or GitHub action to periodically scrape data? Using cURL makes this a breeze. It‘s trivial to schedule cURL commands and capture the output.

5. cURL is perfect for testing and debugging. Trying to figure out why your scraper isn‘t working? Use cURL to interact with the site manually and pinpoint the issue. cURL makes it easy to inspect headers, cookies, status codes and response bodies when things aren‘t working as expected.

Now that we‘ve seen why cURL is so widely used, let‘s dive into some more advanced usage for web scraping.

Using Proxies with cURL

When you‘re scraping a large number of web pages, it‘s a good idea to use proxies to distribute your requests across many IP addresses. This helps avoid triggering rate limits and IP bans that can shut down your web scraper.

Fortunately, cURL has built-in support for making requests through HTTP, HTTPS and SOCKS proxies. To use a proxy with cURL, simply pass the proxy details with the -x flag:


curl -x http://user:[email protected]:3128 http://example.com


This will route the request to http://example.com through the HTTP proxy at proxy.com on port 3128, using the specified username and password for authentication if required.

You can also set a default proxy that will be used for all cURL requests like this:


export http_proxy="http://user:[email protected]:3128"
export https_proxy="http://user:[email protected]:3128"


With those environment variables set, you can omit the -x flag and your requests will automatically use the specified proxy.

If you‘re doing heavy web scraping, it‘s best to use a premium proxy service that‘s optimized for high concurrency and request volumes. Rotating through a large pool of proxies will help keep your scraper running smoothly.

Modifying Headers and the User Agent

Some websites attempt to block web scrapers by looking for signatures in the HTTP headers of incoming requests. One common tactic is examining the User-Agent header to determine if the traffic is coming from a real browser or an automated tool.

With cURL, it‘s easy to modify your request headers to make your scraper appear more like a regular user. The -H flag allows you to pass custom headers:


curl -H "User-Agent: Mozilla/5.0 Firefox/79.0" https://example.com


Here we‘re setting the User-Agent to a realistic browser signature, in this case Firefox 79 on desktop. Websites are less likely to block requests containing common user agent strings vs ones that are blank or contain "curl" or "python".

Along with User-Agent, some other headers you may want to set for web scraping include:

• Referer – Indicates the page that linked to this URL
• Accept – Specifies what content types are accepted
• Cookie – Sends cookie data
• Authorization – Provides authentication credentials

Logging In and Maintaining Sessions

So far we‘ve looked at scraping publicly accessible pages. But what if the data you need is behind a login form?

With cURL, handling authentication and maintaining a session is fairly straightforward. The basic process is:

1. Submit a POST request to the login URL containing your username and password
2. Capture the session cookie that‘s returned on successful login
3. Include that session cookie in all subsequent page requests

Here‘s what that might look like in practice:

curl -c cookies.txt -d "user=bob&pass=123" https://example.com/login

curl -b cookies.txt https://example.com/members_only


The -c flag tells cURL to write any received cookies to the specified file. We then use -b to read in that cookie file when accessing the protected page, allowing us to maintain the logged-in session.

Some websites use additional CSRF tokens or non-cookie based session handling which can be a bit trickier. But in most cases, capturing and replaying the right cookies is all you need to access logged-in content.

Putting It All Together

As you can see, cURL is an incredibly powerful tool for web scraping. By combining flags, customizing headers, and capturing cookies, you can automate the process of logging into websites, submitting forms, and collecting protected data.

Here‘s an example that puts many of the concepts we‘ve covered together:

export https_proxy=http://user:[email protected]:3128

curl -c cookies.txt \
-H "User-Agent: Mozilla/5.0 Firefox/79.0" \
-d "username=bob&password=123" \
https://example.com/login

curl -b cookies.txt \
-H "User-Agent: Mozilla/5.0 Firefox/79.0" \
-O https://example.com/data_page_1.html
curl -b cookies.txt \
-H "User-Agent: Mozilla/5.0 Firefox/79.0" \
-O https://example.com/data_page_2.html
curl -b cookies.txt \
-H "User-Agent: Mozilla/5.0 Firefox/79.0" \
-O https://example.com/data_page_3.html


This script logs into a website through a proxy, captures the session cookie, then uses that cookie to download 3 protected data pages while spoofing its User Agent. With a bit of bash scripting, you could easily expand this to scrape hundreds or thousands of pages.

Alternatives to cURL

While cURL is great for many scraping workflows, it‘s not the only option out there. Here are a few alternatives you may want to consider:

• Wget – Wget is another command line utility for downloading files over HTTP and FTP. It has many of the same capabilities as cURL but some differences in syntax and functionality.

• Python Scrapy – Scrapy is a popular Python framework designed specifically for web scraping. It includes many high level features like built-in support for extracting data using CSS selectors and XPath expressions.

• Node.js Puppeteer – Puppeteer is a Node library that allows you to control a headless Chrome browser. This is useful for scraping JavaScript heavy sites where you need to execute scripts and fully render the page.

• Web Scraping APIs – If you don‘t want to build and maintain your own web scrapers, you can often find existing APIs that will provide the data you need in a structured format. This can be a big time saver for one-off projects.

Ultimately, the best web scraping tool depends on your specific needs and preferences. But for many jobs, it‘s hard to beat the simplicity and power of cURL.

Wrap Up

In this guide, we‘ve taken a deep dive into using cURL for web scraping. We‘ve covered:

• What cURL is and how to install it
• Basic usage and common flags
• Using proxies to distribute requests
• Modifying headers to blend in with browsers
• Logging in and handling session cookies
• Scripting multi-page scraping tasks

As you‘ve seen, cURL is an incredibly versatile tool that allows you to automate all kinds of interactions with websites. Whether you just need to download a few public pages or fully log in and navigate a complex web app, cURL has you covered.

So the next time you need to collect some data from the web, consider giving cURL a try. With its wide availability, extensive feature set, and ease of use, cURL is truly the Swiss Army Knife for web scraping.