What is cURL Command Line Tool Explained
This article provides a clear overview of cURL, explaining what the tool is, how it functions, and why it is essential for developers and system administrators. You will learn about its supported protocols, common use cases, and basic command examples to help you get started with transferring data over network protocols.
Understanding cURL
cURL, which stands for “Client URL,” is a highly popular, open-source command-line tool and library used for transferring data with URLs. Designed to work without user interaction, cURL allows users to connect to servers, send requests, and retrieve data directly from the terminal or via automated scripts.
At its core, cURL is powered by libcurl, a robust transfer library that can be integrated into various programming languages and software applications.
Key Features of cURL
- Wide Protocol Support: cURL supports a vast array of network protocols, including HTTP, HTTPS, FTP, SFTP, FTPS, SCP, SMTP, POP3, IMAP, and LDAP.
- Platform Independent: It is highly portable and runs on virtually every operating system, including Linux, macOS, and Windows.
- Automation Friendly: Because it operates via the command line, it is easily integrated into shell scripts, cron jobs, and CI/CD pipelines.
- Diagnostic Capabilities: Developers frequently use cURL to debug network connections, inspect HTTP headers, and test API endpoints.
How to Use cURL: Basic Examples
The syntax for a basic cURL command is straightforward:
curl [options] [URL]Here are some of the most common ways developers use cURL:
1. Fetching a Web Page
To retrieve the HTML content of a website and display it in your terminal, simply provide the URL:
curl https://example.com2. Downloading a File
To download a file and save it with a specific name, use the
-o (lowercase) option:
curl -o download.html https://example.comTo save the file with its original remote name, use the
-O (uppercase) option:
curl -O https://example.com/file.zip3. Sending POST Requests
cURL is widely used for testing APIs. To send a POST request with
data, use the -X option to specify the method and
-d to specify the payload:
curl -X POST -d "username=admin&password=123" https://api.example.com/login4. Viewing HTTP Headers
If you want to inspect only the response headers (such as status
codes and content type) without downloading the page body, use the
-I option:
curl -I https://example.comAccessing the Documentation
Because cURL has hundreds of command-line flags and options to customize headers, manage cookies, use proxies, and handle authentication, referring to the official manuals is highly recommended. You can find the complete list of options, protocols, and detailed guides by visiting the cURL online documentation.