First released in 1996 by Daniel Stenberg, who was creating a bot that would download data over HTTP, cURL has grown immensely to support numerous internet protocols. Currently, it is a free, powerful, open-source, cross-platform command-line tool powered by a vast library known as libcurl. In this beginner’s guide, we will detail what cURL is, how to set it up, and what it does.
Setting up cURL
cURL is a free cross-platform tool that is supported by numerous operating systems powering computers, mobile phones, and servers. This is because the libcurl library can be built on and works similarly on multiple operating systems. These include Android, Microsoft Windows, iOS, Symbian, Blackberry 10, UnixWare, macOS, Linux, DOS, NetWare, and more.
There are different ways to install cURL based on the OS and system architecture. You can use the cURL download wizard, which will automatically help you select what to download. Alternatively, curl.se offers a comprehensive list of download packages for various operating systems. The available resources, therefore, make it easy to get started.
For beginners, cURL may seem complex owing to the fact that it is a non-verbose tool with numerous hidden options and configurations. However, this should not be a deterrent as this tool offers the “verbose” feature that explains the various functions in detail. Additionally, cURL is an extremely powerful tool that, once understood, opens users up to numerous capabilities. In fact, there are plenty of ways through which programmers and data scientists can use cURL.
Uses of cURL
cURL is mainly used to transfer data through various internet protocols. However, its utility is not just limited to this single function. Rather, this command-line tool can be applied in various other computing and networking scenarios. It is this fact that has made it a powerful tool for developers.
cURL is used for the applications:
- Data transfer
- Downloading files via internet protocols and web scraping
- Uploading data
- Testing REST API
- Debugging
- Sending and reading emails
- Connecting proxy servers (cURL with proxy commands)
- Storing usernames and passwords as a .netrc file (for remote FTP servers running on Unix operating system)
- Defining timeouts, including maximum time allowed to create a connection with the host before disconnecting
- Copy as cURL, which uses the command line to reproduce an operation just completed on a browser
This article will mainly focus on a few important use cases.
Data Transfer
cURL supports multiple internet protocols. These include: HTTP, HTTPS, SOCKS, POP3, POP3S, TFTP, TELNET, SMTP, SMTPS, SMB, SMBS, SFTP, SCP, RTMP, RTSP, MQTT, LDAP, LDAPS, DICT, IMAP, IMAPS, GOPHER, GOPHERS, FILE, FTP, and FTPS.
An internet protocol is a method through which data is sent via the internet from one computer to another. Thus, by virtue of supporting approximately all protocols, cURL facilitates the transfer of data.
Web Scraping
You can use cURL with PHP to create a web scraper that automatically sends HTTP requests (using cURL functions and commands) and parses the data (using PHP lines of code). Alternatively, you can use cURL to download URLs or the files named in the URL. This second method enables you to download HTML or PDF files. However, unlike the first one, it does not parse the data, meaning the downloaded file will contain unstructured data.
And as detailed below, you can use cURL with proxy to increase your online anonymity during web scraping. You can find more info about using cURL with proxies here.
Sending and Reading Emails
cURL supports IMAP, IMAPS, POP3, and POP3S protocols, which are used to download and read emails from servers. It also supports the Simple Mail Transfer Protocol (SMTP) and SMTPS, which can be used to send emails with cURL.
Debugging
In the event that you do not understand the exact function cURL has undertaken, you can opt to make the tool verbose using the curl -v command. This command prompts cURL to explain what it is doing, enabling you to solve any issue you may have faced before.
Timeouts
A connection may take too long to load as a result of fragile or unreliable network operations. To avoid wasting time waiting on the connection to go through, particularly in automated requests, you can set the maximum time using cURL commands.
cURL with Proxy
cURL with proxy commands enables you to connect to internet protocol-based proxies such as HTTP, HTTPS, and SOCKS. This often adds an extra layer of anonymity as the proxies assign your requests a new IP address. In this regard, you can use cURL with proxy commands alongside web scraping functions.
Conclusion
cURL is a powerful, multi-platform tool that offers numerous capabilities. It is also easy to set up, thanks to readily available resources for each operating system. Once you have installed cURL, you can use it to execute numerous functions. These include: data transfer, sending and reading emails, routing the requests through proxies using cURL with proxy commands, scraping data from websites, and more.
