How to Send POST Requests With cURL

In this tutorial, you're going to learn how to send cURL POST requests. cURL is a powerful command-line tool for transferring data over various network protocols, including HTTP, HTTPS, FTP, and more. Since POST is a request method of HTTP & HTTPS protocols, cURL POST request is a one-line command that you can easily run in your terminal.

Tutorial: Sending POST requests

First, install cURL if you haven't installed it already. You can find the installation instructions in our How to Use cURL With Proxy blog post. Next, take a look at the table below:

This table represents all the necessary command-line options of the cURL command that you'll be using in the next few sections. You don't need to memorize all of them right away, just briefly go over them. Once you start to use cURL requests daily, they'll become part of your muscle memory while working in a terminal. And whenever you need, you can always access all the available cURL options including the above using the --help option for more detailed descriptions:

curl --help

The basic cURL POST request syntax is as below:

curl -X POST -d "Hello" https://example.com/api

Notice the -X flag followed by POST. It tells cURL to make a POST request using the typical HTTP POST method, and the -d flag sets request data as Hello and sends it to the HTTP server at https://example.com/api. The -X flag is the short form of the command line option --request. Check out the above table for learning all the long forms of the various command line options.

Specifying the Content-Type

Like any HTTP request, cURL POST requests can also have custom headers. Here, using the header flag will force cURL to use any specific Content-Type header of your choice.

curl -X POST -H "Content-Type: text/plain" -d "Hello" https://example.com/api

In the above cURL POST command, there's an additional -H flag that lets users send custom HTTP request headers via cURL. In this case, by specifying the Content-Type header as text/plain you’re letting the web server know that the request body data is in TEXT format. 

Posting JSON

It’s also possible to send JSON data in the cURL POST request body. All you need to do is set the appropriate Content-Type header and pass the JSON body with either the -d flag or cURL --data option. This command will make a cURL POST request with the JSON format data specified in the argument.

curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' https://example.com/api

If you need a straightforward way to create a JSON code from a cURL command, use this cURL to JSON converter.

Posting XML

Similar to JSON data, you can also use cURL POST with body in XML format. You'll have to make changes to the request header and set it to application/xml.

curl -X POST -H "Content-Type: application/xml" -d '<?xml version="1.0" encoding="UTF-8"?><root><name>John Doe</name><age>30</age></root>' https://example.com/api

Sending a file/multiple files via POST

To send form data or a file via cURL POST, you'll have to use the -F flag. Pay attention to the capitalization of the letter “F”. All of the cURL flags or command-line options are case-sensitive and should look like the following cURL POST example:

curl -X POST -F "file=@/path/to/img.png" https://example.com/api/upload

As you can see, the above cURL POST request is uploading an image local file. Right after the -F the path of the image was given. Keep in mind cURL supports both local and remote file transfers. You can also use multiple -F flags to send multiple files to the server as shown below:

curl -X POST -F "file=@/path/to/img1.png" -F "file=@/path/to/img2.png" https://example.com/api/upload

The same HTTP request methods apply when working with form data, where you can specify each form field individually. This way, you can send form data, including binary data, and cURL will handle the completed transfer automatically.

Sending authentication credentials

You can use the -u flag or the --user option to specify the username & password for basic authentication. cURL will automatically create the Authorization header based on the received data. 

curl -u username:password https://example.com/login

You’ll have to replace username and password with the actual authentication credentials. Also, don’t forget to replace the example URL with your own when making cURL requests.

Conclusion

cURL is a lightweight yet powerful tool for sending POST requests from CLI. With just a single line of command, you can easily transmit data in various formats such as JSON, XML, or file uploads and form data. cURL's simplicity and flexibility make it a popular choice for developers. While it may not offer a graphical interface, cURL provides a versatile and efficient way to interact with servers. Whether you're a seasoned developer or a complete beginner, mastering cURL is a valuable skill that’ll help you in various stages of your career. If you're new to cURL, we recommend reading our article on how to send GET requests with cURL or trying our cURL converter tool.

You can also check out the How to Use cURL With REST API and How to Use cURL With Python articles available on our blog. Additionally, you can learn how to use cURL OPTIONS requests for web scraping. As usual, if you have any questions, please contact us at hello@oxylabs.io or via the live chat – our professional team is always ready to provide you with the needed assistance.