The minimum you need to know to test your APIs with CURL
CURL is a command-line tool that allows you to transmit data with URL syntax, supporting a myriad of protocols (DICT, FILE, FTP, FTPS, GOPHER, GOPHERS, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, MQTT, POP3, POP3S, RTMP, RTMPS, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET, TFTP, WS and WSS). In this article, I will focus on using CURL to make HTTP requests to APIs, which, at least for me, is the most common use.
Installation
CURL is already installed on most Linux distributions and recent versions of Windows. To check if it's installed, just run the curl command in the terminal. If you don't have CURL installed, you can install it with the command sudo apt install curl (Ubuntu/Debian) or sudo yum install curl (CentOS/Fedora) or winget install curl (Windows).
Oh, and as it is common for us to work with REST APIs in web development, another command-line tool that will be useful to us is jq, which serves to format JSON in the terminal. To install jq, just run the command sudo apt install jq (Ubuntu/Debian) or sudo yum install jq (CentOS/Fedora) or winget install jqlang.jq (Windows).
Our example API
For didactic purposes, I will use DummyJSON as an API.
Making a GET request
To make a GET request, just run the curl command followed by the URL you want to access. For example, to request data for product 1, just run the command curl https://dummyjson.com/products/1.
And, to format the output, just add a | jq at the end of the command:
Making a POST, PUT, PATCH or DELETE request with JSON in the body
To make a POST request, just run:
The curl will take care of adding the headers Content-Type: application/json and Accept: application/json. If you want to make a PUT, PATCH or DELETE request, add the -X option followed by the HTTP method you want to use. For example, to make a PUT, run:
You can also send a JSON file instead of typing the JSON in the terminal by putting an @ in front of the file name:
Or passing data from stdin (note that I use @- instead of @ to indicate that the data will come from stdin):
Making a request with headers
To make a request with headers, just run the curl command followed by the URL you want to access, and the -H option followed by the header you want to send. So, to send a Bearer Token, you would run the following command:
Some Exercises
Julia Evans published a few exercises to help you become fluent in curl. It should be worth to take a look at this post in her blog.