In the vast landscape of Linux, tools exist that, once mastered, can unlock a new level of productivity and understanding. One such tool is cURL, a command-line utility for data transfer across many protocols. This guide thoroughly explores the cURL command, its syntax, options, and practical examples demonstrating its versatility and power.
Introduction to cURL Command
cURL, an acronym for “Client for URLs,” is a free, open-source command-line tool for transferring data using various network protocols. Its support for protocols like HTTP, HTTPS, FTP, and SFTP, among others, makes it a versatile tool for interacting with servers and APIs. Whether fetching a webpage, downloading a file, or interacting with a RESTful API, cURL has you covered.
The Syntax of cURL Command
The cURL command follows a simple syntax:
curl [options] [URL]In this syntax:
options: These are the parameters that modify the behavior of cURL.URL: This is the address of the file or resource you want to interact with.
cURL Command Options
cURL offers a wide range of options that allow you to customize its behavior. Here are some of the most commonly used options:
-O: Downloads the file from the specified URL.-I: Fetches the HTTP-header from the server.-u: Specifies the user credentials for server authentication.-d: Sends the specified data in a POST request to the server.-x: Specifies the proxy address to use for the requests.
Diving into cURL: 30 Examples
Now, let’s delve into some practical examples of using the cURL command. Each example will be prefaced with an explanation and followed by a demonstration of the output.
Example 1: Fetching Data from a URL
The most basic use of cURL is to fetch the contents of a webpage. Here’s how you can do it:
curl https://www.example.comThis command fetches the HTML content of the webpage at https://www.example.com.
Example 2: Downloading a File
cURL can also be used to download files from the internet. Here’s an example:
curl -O https://www.example.com/file.txtThis command downloads the file file.txt from https://www.example.com and saves it in the current directory.
Example 3: Sending a POST Request
You can use cURL to send POST requests to a server. Here’s how:
curl -d "param1=value1¶m2=value2" -X POST http://www.example.comThis command sends a POST request to http://www.example.com with the data param1=value1¶m2=value2.
Example 4: Fetching HTTP Headers
If you want to fetch the HTTP headers from a server, you can use the -I option. Here’s an example:
curl -I https://www.example.comThis command fetches the HTTP headers from https://www.example.com.
Example 5: Using a Proxy
If you need to use a proxy, you can specify it using the -x option. Here’s how:
curl -x http://proxy.example.com:8080 https://www.example.comThis command sends the request to https://www.example.com through the proxy at http://proxy.example.com:8080.
Example 6: Sending Cookies
You can send cookies along with your request using the -b option. Here’s an example:
curl -b "name=value" https://www.example.comThis command sends a cookie with name=value to https://www.example.com.
Example 7: Sending User Agent
Websites often use the user agent to deliver content suitable for the client’s browser. To send a user agent with your request, use the -A option:
curl -A "Mozilla/5.0" https://www.example.comThis command sends a request to https://www.example.com with the user agent set as Mozilla/5.0.
Example 8: Following Redirects
Some URLs redirect to other URLs. To follow these redirects, use the -L option:
curl -L https://www.example.comThis command follows any redirects from https://www.example.com.
Example 9: Saving Output to a File
To save the output of a cURL command to a file, use the -o option:
curl -o output.html https://www.example.comThis command saves the output of https://www.example.com to output.html.
Example 10: Uploading Files with FTP
cURL can upload files to a server using FTP. Here’s how:
curl -T file.txt ftp://ftp.example.com --user username:passwordThis command uploads file.txt to ftp://ftp.example.com using the provided username and password.
Example 11: Resuming a Download
If a download gets interrupted, you can resume it with the -C - option:
curl -C - -O https://www.example.com/file.txtThis command resumes the download of file.txt from https://www.example.com.
Example 12: Downloading Multiple Files
To download multiple files, specify multiple URLs:
curl -O https://www.example.com/file1.txt -O https://www.example.com/file2.txt
This command downloads file1.txt and file2.txt from https://www.example.com.
Example 13: Sending a DELETE Request
To send a DELETE request, use the -X DELETE option:
curl -X DELETE https://www.example.com/resourceThis command sends a DELETE request to https://www.example.com/resource.
Example 14: Verbose Output
For detailed information about the request and response, use the -v option:
curl -v https://www.example.comThis command provides verbose output for the request to https://www.example.com.
Example 15: Silent Mode
To suppress the progress meter and error messages, use the -s option:
curl -s https://www.example.comThis command fetches the content of https://www.example.com in silent mode.
Example 16: Displaying the Download Progress
To display the download progress in a more readable format, use the # option:
curl -# -O https://www.example.com/file.txtThis command downloads file.txt from https://www.example.com and displays the progress as a progress bar.
Example 17: Sending JSON Data
To send JSON data in a POST request, use the -H option to set the content type:
curl -d '{"key1":"value1", "key2":"value2"}' -H "Content-Type: application/json" -X POST https://www.example.com
This command sends a POST request with JSON data to https://www.example.com.
Example 18: Using cURL with an API
cURL is often used to interact with APIs. Here’s an example:
curl -H "Authorization: Bearer YOUR_TOKEN" https://api.example.com
This command sends a request to https://api.example.com with an authorization header.
Example 19: Downloading Files in the Background
To download a file in the background, use the -O option with an ampersand at the end:
curl -O https://www.example.com/file.txt &This command downloads file.txt from https://www.example.com in the background.
Example 20: Sending Data from a File
To send data from a file in a POST request, use the @ symbol:
curl -d @data.txt -X POST https://www.example.comThis command sends a POST request with the data from data.txt to https://www.example.com.
Example 21: Fetching Content from FTP Server
cURL can be used to fetch content from an FTP server. Here’s how:
curl ftp://ftp.example.com/file.txt --user username:passwordThis command fetches file.txt from ftp://ftp.example.com using the provided username and password.
Example 22: Fetching Content from a Password-Protected Website
To fetch content from a password-protected website, use the -u option:
curl -u username:password https://www.example.comThis command fetches the content from https://www.example.com using the provided username and password.
Example 23: Fetching Content from a Website with SSL
To fetch content from a website with SSL, use the -k option:
curl -k https://www.example.comThis command fetches the content from https://www.example.com, ignoring any SSL certificate warnings.
Example 24: Sending a PUT Request
To send a PUT request, use the -X PUT option:
curl -X PUT -d "data" https://www.example.com/resourceThis command sends a PUT request with the data “data” to https://www.example.com/resource.
Example 25: Fetching the Response Headers
To fetch only the response headers, use the -I option:
curl -I https://www.example.comThis command fetches only the response headers from https://www.example.com.
Example 26: Fetching Content from a Website with Cookies
To fetch content from a website with cookies, use the -b option:
curl -b cookies.txt https://www.example.comThis command fetches the content from https://www.example.com using the cookies stored in cookies.txt.
Example 27: Fetching Content from a Website with Custom Headers
To fetch content from a website with custom headers, use the -H option:
curl -H "Custom-Header: Value" https://www.example.comExample 28: Fetching Content from a Website with a Timeout
To fetch content from a website with a timeout, use the -m option:
curl -m 10 https://www.example.comThis command fetches the content from https://www.example.com with a timeout of 10 seconds.
Example 29: Fetching Content from a Website in Verbose Mode
To fetch content from a website in verbose mode, use the -v option:
curl -v https://www.example.comThis command fetches the content from https://www.example.com in verbose mode, displaying detailed information about the request and response.
Example 30: Fetching Content from a Website and Displaying the Progress Meter
To fetch content from a website and display the progress meter, use the -# option:
curl -# https://www.example.comThis command fetches the content from https://www.example.com and displays the progress meter.
Conclusion
In conclusion, our comprehensive guide, “cURL Command in Linux: 30 Powerful Examples Unveiled,” has provided a deep dive into the practical applications of the cURL command in Linux. We’ve explored a variety of examples, each showcasing a unique aspect of cURL’s capabilities, from fetching data from a URL to interacting with APIs and handling data transfer across diverse network protocols.