cURL, short for client uniform resource locator, is a free, open-source software project that facilitates data transfer using over 22 internet protocols. It comprises a command-line tool with tens of functions supported by a comprehensive and powerful library known as libcurl. Though cURL and libcurl enable programmers to perform numerous tasks listed below, this article will mainly focus on how cURL is used for web scraping.
Uses of cURL
Contents
Programmers and data scientists use cURL for the following applications:
- Data transfer
- Downloading and storing files (data collection and web scraping)
- Uploading files onto a server using the File Transfer Protocol (FTP)
- Sending and reading emails
- Copying recent browser operations using the copying with cURL command
- Routing requests through proxies with the help of the cURL with proxy commands
- Defining timeouts to reduce time wastage, particularly in automated browsing
- Verifying a Secure Sockets Layer (SSL) certificate
- Automatic logins in FTP servers running on the Unix operating system
- Testing and debugging URL to determine whether the web address is live.
Why cURL’s Popularity is Growing
Despite having numerous hidden capabilities and being non-verbose, cURL’s popularity is increasing among the developer community. This is because of several reasons, including:
- cURL is powerful, as evidenced by its numerous use cases, some of which we have not listed above
- cURL is a cross-platform tool, meaning it can be installed on multiple operating systems (it also runs similarly on all platforms)
- It is a free
- cURL is open-source, meaning programmers can contribute to the project
- The command-line tool supports multiple protocols, including HTTP, HTTPS, FTP, FTPS, GOPHER, GOPHERS, POP3, POP3S, SMTP, SMTPS, SCP, SMB, SMBS, MQTT, DICT, FILE, RTMP, and more
Web Scraping and Data Collection Using cURL
cURL supports data transfer via multiple internet protocols. But data transfer is just one aspect of data collection; the other is retrieving the transferred information. There are two main ways to achieve the latter using cURL. These include:
- Creating a web scraper using PHP
- Downloading and storing URL files
Using cURL in PHP
Using a PHP module, you can create a few lines of code that enable PHP programs to access cURL commands and functions within the PHP ecosystem. As a result, you can use cURL with PHP to extract data from websites. cURL enables the PHP system to make HTTP requests to the website(s) from which you wish to extract data.
cURL comes in handy in this particular use case because web scraping normally involves the issuance of multiple HTTP requests. With cURL being well suited for automating repetitive processes such as this, you as the developer can concentrate on other important functions of a web scraper. Simply put, the PHP module allows you to combine the cURL functions with lines of code written in PHP.
As a result, you can create a PHP cURL web scraper that not only makes HTTP requests but also parses the responses for specific datasets, checks whether the webpage contains images, and more.
Downloading and Storing URL Files
cURL facilitates data transfer from a web client to a server and vice versa. When this data is sent from the server to a browser, it can be downloaded and stored locally. This, therefore, means that you can use cURL to scrape data from websites. Ordinarily, the command below enables cURL to download a URL.
curl http://example.com
However, the URL may also feature a file name such as PDF or HTML. In that case, you can use cURL to download that specific file. For this, you can use the command below:
curl -O http://example.com/file.pdf where the -O is in uppercase or
curl -o file.pdf http://example.com/file.pdf where the -o is in lowercase
It is noteworthy that while both of these commands serve the same function, to download the PDF or HTML file defined in the URL, they defer in their lengths and, therefore, simplicity.
cURL with Proxy and Web Scraping
In addition to using cURL to scrape data from websites, you can use the cURL with a proxy command to route web requests through supported proxy servers. As an internet protocol-based tool, cURL detects and creates HTTP, HTTPS, SOCKS (version 4 and 4a), and SOCKS5 proxies.
Using these types of proxies allows you to assign the web requests a new IP address, promoting online anonymity. This makes cURL with proxy commands a vital addition to web scraping. This is particularly important since evolving web development has given rise to anti-scraping tools, the most common of which is IP blocking. Click here to read more about using cURL with proxies.
Conclusion
As a powerful data transfer tool that supports numerous internet protocols, cURL has proven to be an effective tool in promoting data collection from websites. It is used to automate repetitive processes such as HTTP requests when creating PHP web scrapers. Separately, it can be used to download URL files as well as files defined in the URL. Additionally, programmers can use cURL with proxy commands to create proxies.