curl Command in Linux with Examples

The curl command in Linux is a command-line tool used to transfer data between a system and a server using different network protocols. It is widely used for fetching web content, testing APIs, and sending or receiving data over the network.

• Supports multiple protocols such as HTTP, HTTPS, FTP, and SCP
• Used to download, upload, and send data from the terminal
• Helpful for testing REST APIs and web services
• Works with headers, authentication, and data formats like JSON

Example 1: Fetching Data Using curl Command

The simplest use of curl is to fetch a URL. By default, curl prints the content of the URL directly to your terminal (stdout).

curl https://example.com

• This command will retrieve the HTML content of the specified URL and display it in the terminal.  

Example 2:

curl https://www.geeksforgeeks.org//%3C/span>

This should display the content of the URL on the terminal. The URL syntax is protocol dependent and multiple URLs can be written as sets like: 

curl http://site.{one, two, three}.com

URLs with numeric sequence series can be written as: 

curl ftp://ftp.example.com/file[1-20].jpeg

Progress Meter: curl displays a progress meter during use to indicate the transfer rate, amount of data transferred, time left, etc. 

curl -# -O ftp://ftp.example.com/file.zip
curl --silent ftp://ftp.example.com/file.zip

If you like a progress bar instead of a meter, you can use the -# option as in the example above, or --silent if you want to disable it completely. 

Output:

Examples of Curl with Options Reference

Given below are some examples demonstrating the use of the curl command in Linux along with their options.

Syntax of curl Command

curl [options] [URL]

Here,

• [options]: Can be various command-line flags that modify the behavior of curl
• [URL]: Specifies the location from which to fetch or send data.

1. -O Option

This option downloads the file and saves it with the same name as in the URL. 

Syntax:

curl -O [URL...]

Example:

curl -O ftp://speedtest.tele2.net/1MB.zip

Output:

2. -C - Option:

This option resumes download which has been stopped due to some reason. This is useful when downloading large files and was interrupted. 

Syntax:

curl -C - [URL...]

Example:

curl -C - -O ftp://speedtest.tele2.net/1MB.zip

Output:

3. --limit-rate Option:

This option limits the upper bound of the rate of data transfer and keeps it around the given value in bytes. 
Syntax:

curl --limit-rate [value] [URL]

Example:

curl --limit-rate 1000K -O ftp://speedtest.tele2.net/1MB.zip

Output:

The command limits the download to 1000K bytes.

4. -u Option:

curl also provides options to download files from user authenticated FTP servers. 

Syntax:

curl -u {username}:{password} [FTP_URL]

Example:

curl -u demo:password -O ftp://test.rebex.net/readme.txt

Output:

5. -T Option:

This option helps to upload a file to the FTP server. 

Syntax:

curl -u {username}:{password} -T {filename} {FTP_Location}

If you want to append an already existing FTP file you can use the -a or --append option.

6. --libcurl Option:

This option is appended to any curl command, it outputs the C source code that uses libcurl for the specified option.

Syntax:

curl [URL...] --libcurl [filename]

Example:

curl https://www.geeksforgeeks.org// > log.html --libcurl code.c

Output:

The above example downloads the HTML and saves it into log.html and the code in code.c file. The next command shows the first 30 lines of the code.

Some Other uses of curl Command

The curl command supports multiple protocols, allowing it to perform tasks like sending emails and fetching dictionary meanings directly from the terminal.

1. Sending mail:

If we can transfer data over different protocols, including SMTP, we can use curl to send mails. 

Syntax:

curl --url [SMTP URL] --mail-from [sender_mail] --mail-rcpt [receiver_mail] -n --ssl-reqd -u {email}:{password} -T [Mail text file] 

2. DICT protocol:

DICT protocol which can be used to easily get the definition or meaning of any word directly from the command line. 

Syntax:

curl [protocol:[dictionary_URL]:[word]

Example:

curl dict://dict.org/d:overclock

Output:

3. Handling HTTP Requests Using curl Command

'curl' is the perfect tool for interacting with REST APIs. The `curl` command allows you to send custom HTTP requests with various methods such as GET, POST, PUT, DELETE, etc. For example, to send a GET request:

curl -X GET https://api.sampleapis.com/coffee/hot%3C/span>

In the same way, to send a POST request with data:

curl -X POST -d "key1=value1&key2=value2" https://api.sampleapis.com/coffee/hot%3C/span>

In this case, the `-d` flag is used to send data to be sent with the request.

4. Downloading Files Using curl Command

curl is also generally used to download a file from the web. To download a file, you simply provide the URL of the file as the argument:

-o: saves the downloaded file to the local host with the specified name in parameters.

Syntax:

curl -o [file_name] [URL...]

Example:

curl -o hello.zip ftp://speedtest.tele2.net/1MB.zip

Output:

The above example downloads the file from the FTP server and saves it with the name hello.zip.

5. Uploading Files

If you want to upload a file to a server, for example using FTP (File Transfer Protocol), curl can do that in just one line:

curl -T uploadfile.txt ftp://example.com/upload/

• -T uploadfile.txt: This tells curl which file to upload (in this case, a file called uploadfile.txt).
• ftp://example.com/upload/: This is the destination FTP URL where the file will be uploaded.

6. Handling Authentication

Sometimes the API or site you're trying to access is protected with a username and password. In those cases, you can put your credentials in the command itself using the -u flag.

curl -u username:password https://example.com//api%3C/span>

• -u username:password: This sends your login details securely with the request.
• https://example.com//api%3C/strong>: The protected API or resource you want to access.