# The Power of cURL > cURL is a command-line tool used to transfer files and invoke APIs over protocols like HTTP, HTTPS, and FTP. Learn how to send GET, query params, URI params, headers, and POST requests, plus how to print output. - **Author:** Whitney Akinola - **Published:** Mar 30, 2021 - **Category:** Tutorials - **Tags:** MuleSoft, API, cURL - **Source:** https://prostdev.com/post/the-power-of-curl --- ## Series: The Power of cURL (Part 1 of 2) 1. The Power of cURL (this post) 2. [The Power of cURL - Part II](https://prostdev.com/post/the-power-of-curl-part-ii) --- [Advanced Rest Client](https://install.advancedrestclient.com/install), [Postman](https://www.postman.com/downloads/) and [SoapUI](https://www.soapui.org/downloads/soapui/) are top API clients you may have used while building or testing API integrations. These applications are useful. However there are cases where invoking the API from the command line is advantageous and is made possible through **cURL.** ## What is cURL? [cURL](https://curl.se/) is a tool used to transfer files. The cURL command can be used inside scripts or from the command line. cURL provides support for common protocols like HTTP, HTTPS, FTP and much more. This article will focus on using the cURL command to invoke integrations that use HTTP. The cURL commands provided in this article will be demonstrated by invoking a sample API built in Mule 4, running on my local machine. Let’s get started! ## How do I start? Open your command prompt (Windows) or terminal (Mac/Linux). Run ```bash curl ``` ![Git Bash terminal where running curl prints "try 'curl --help' for more information"](../../assets/blog/the-power-of-curl-1.png) Look for the following output: ```bash curl: try 'curl --help' for more information ``` This is a good indicator that cURL is installed on your local machine. If not, you will need to do a fresh install of cURL. Download cURL [here](https://curl.se/download.html). cURL commands typically use the following syntax: ```bash curl [options] [url] ``` ## Need help? Use the --help option to provide a list of options. ```bash curl --help ``` ![curl --help output listing common options like --data, --header, --output, and --verbose](../../assets/blog/the-power-of-curl-2.png) Use the --manual option to reference the “man” page (or manual). ```bash curl --manual ``` ![curl --manual page showing the cURL name, synopsis, and description of supported protocols](../../assets/blog/the-power-of-curl-3.png) > [!NOTE] > Since I am using a Windows machine, I often use the command line from a Git Bash terminal. ## Demo Time The remainder of this article will focus on HTTP. All demonstrated cURL command examples will be HTTP requests (unless otherwise specified) and invoked against a simple Mule API running on my local machine. The API takes in the HTTP request and provides a breakdown of the request in the response. REQUEST OPTION: To create an HTTP/HTTPS request. Use the --request option. SYNTAX: ```bash curl --request '' ``` > [!NOTE] > URL will include the protocol (http/https). ### **GET** GET requests can be written in two formats: 1) Short-hand SYNTAX: ```bash curl '' ``` EX: ```bash curl 'http://localhost:8081/curl/helloget' ``` 2) Long-hand SYNTAX: ```bash curl --request GET '' ``` EX: ```bash curl --request GET 'http://localhost:8081/curl/helloget' ``` ![curl GET request to /curl/helloget and the JSON response echoing the request method and path](../../assets/blog/the-power-of-curl-4.png) ### **QUERY PARAMS** SYNTAX: ```bash curl --request '?=...&=' ``` EX: ```bash curl --request GET 'http://localhost:8081/curl/helloget?firstname=Daffy&lastname=Duck' ``` ![curl GET with firstname and lastname query params echoed back in the response queryParams](../../assets/blog/the-power-of-curl-5.png) ### **URI PARAMS** SYNTAX: ```bash curl --request '/' ``` EX: ```bash curl --request GET 'http://localhost:8081/curl/helloget/1' ``` ![curl GET to /curl/helloget/1 with the uriParams id of 1 echoed in the response](../../assets/blog/the-power-of-curl-6.png) ### **HEADERS** SYNTAX: ```bash curl --request '' \ --header ':' ``` *Single Header* EX: ```bash curl --request GET 'http://localhost:8081/curl/helloget' \ --header 'Authorization: Bearer xybaneoovganfZbe' ``` ![curl GET with a single Authorization Bearer header echoed in the response headers](../../assets/blog/the-power-of-curl-7.png) *Multiple Headers* EX: ```bash curl --request GET 'http://localhost:8081/curl/helloget' \ --header 'client_id: bond' \ --header 'client_secret: 0007' ``` ![curl GET with client_id and client_secret headers echoed in the response headers](../../assets/blog/the-power-of-curl-8.png) ### **POST** SYNTAX: ```bash curl --request '' \ --header 'Content-Type: ' \ --data-raw '' ``` EX: ```bash curl --request POST 'http://localhost:8081/curl/hellopost' \ --header 'Content-Type: application/json' \ --data-raw '{ "RQ" : {"message" : "hello prostdev readers"}}' ``` ![curl POST to /curl/hellopost with a JSON body echoed back in the response requestBody](../../assets/blog/the-power-of-curl-9.png) ### **Print Output** Interested in saving the output of your API invocation? Use the --output option. SYNTAX: ```bash curl --request --output output.txt ``` EX: ```bash curl --request GET 'http://localhost:8081/curl/helloget'\ --output output.txt ``` ![curl GET request using --output output.txt to save the response to a file](../../assets/blog/the-power-of-curl-10.png) ![The saved output.txt opened in Notepad showing the JSON response from the curl request](../../assets/blog/the-power-of-curl-11.png) ## Lessons Learned - Although quotes are not required around the URL, when sending requests with query parameters make sure you wrap requests around quotes. Without the quotes, I noticed that cURL dropped the query parameters. - Wrap your request URL in “double-quotes” if using command prompt and ‘single-quotes’ if using command line terminal. I found issues with ‘’ and “” between command prompt and command line. - Multi-line in command prompt is different from multi-line on command line. - Add “\” at the end of the line to enter a new line on a multi-line request from the command line. - Add “^” at the end of the line to enter a new line on a multi-line request from the command prompt. ## Conclusion This post invoked an API through HTTP. However, most of the time we invoke APIs over HTTPS. If you are interested in an HTTPS version of this post, please let us know through a comment. If you would like to learn more about cURL, check out the cURL documentation [here](https://curl.se/docs/httpscripting.html). Lastly, I am Whitney Akinola. I’m a fellow MuleSoft Developer and content creator. Feel free to check out my technical content [here](https://www.whitneyakinola.io/blog). --- ## FAQs ### How do I check whether cURL is already installed? Open your command prompt on Windows or terminal on Mac/Linux and run `curl`. If you see the output `curl: try 'curl --help' for more information`, that is a good indicator cURL is installed on your machine. If not, you can do a fresh install from https://curl.se/download.html. ### What's the difference between the short-hand and long-hand way to send a GET request? Both produce a GET request. The short-hand form is just `curl ''`, while the long-hand form spells out the method explicitly as `curl --request GET ''`. ### How do I send query parameters with cURL? Append them to the URL after a `?`, separating multiple pairs with `&`, as in `curl --request GET 'http://localhost:8081/curl/helloget?firstname=Daffy&lastname=Duck'`. The author notes you should wrap requests with query parameters in quotes, because without the quotes cURL dropped the query parameters. ### How do I add headers to a cURL request? Use the `--header` option with a `':'` pair, and repeat `--header` once per header for multiple headers, for example a single `--header 'Authorization: Bearer xybaneoovganfZbe'` or two lines `--header 'client_id: bond'` and `--header 'client_secret: 0007'`. ### How do I save the output of a cURL request to a file? Use the `--output` option followed by a filename, as in `curl --request GET 'http://localhost:8081/curl/helloget' --output output.txt`, which saves the response into that file. ### How do I write a multi-line cURL command? It differs by shell: add `\` at the end of the line to continue onto a new line from the command line terminal, and add `^` at the end of the line to do the same from the Windows command prompt.