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When you read API documentation, you may see requests made by a tool called curl. Here’s an example from Github:
Many APIs explain their documentation through curl. You’ll be able to understand every API documentation if you know curl.
Curl is command line program that lets you send requests.
You can access the command line with the “Terminal” app if you use a Mac. If you use Windows, you can use Command Prompt.
The command line looks scary, but there’s nothing to be afraid of. Here’s an article I wrote that can help you out if you’re scared.
Type curl --version into your command line.
curl --version
If you see a version number, it means you have curl installed. You can move on to the next section.
If you see a “command not found” error, you will need to install curl first.
To send a GET request with curl, you type curl, followed by the endpoint.
curl https://api.github.com
If the server sends you a response, you will see the body of the response in your command line.
If you want to add query parameters to your request, you need to prepend question marks and equal signs with \. Most command line applications will prepend \ for you automatically. This is because ? and = are special characters in the command line.
curl https://api.github.com/users/zellwk/repos\?per_page\=1
To send POST, PUT, PATCH, or DELETE requests, you use a -X flag. Make sure the X in -X is a capital letter. The flags are case sensitive.
curl -X POST https://api.github.com/user/repos
The flag order doesn’t matter. You can put it before or after the url.
curl https://api.github.com/user/repos -X POST
You can perform basic authentication with the -u flag.
curl -X POST -u username:password https://api.github.com/user/repos
Notice the error message changed from “requires authentication” to “problems parsing JSON”. This tells us the authentication is successful.
If you want to authenticate yourself through a token, you need to set an authorization header.
You can set request headers with -H.
curl -H "Authorization: Bearer token_12345" https://api.github.com
To set a second request header, you use another -H.
curl -H "header1: value1" -H "header2: value2" https://api.github.com
To see your own request headers, you can use -v. Your request headers will be prefixed with >.
curl -v -H "Authorization: Bearer token_12345" https://api.github.com
You can also use -v to see response headers. Response headers will be prefixed with <.
If you want to view the response headers only, you can use -I.
curl -I -H "Authorization: Bearer token_12345" https://api.github.com
To send body data, you use -d. Curl will send your data as x-www-form-urlencoded.
curl -X POST https://jsonplaceholder.typicode.com/posts -d title='Article title' -d body='shameless plug'
If you need to encode a value, use --data-urlencode
curl -X POST https://jsonplaceholder.typicode.com/posts -d title='Article title' -d body='shameless plug' --data-urlencode link=https://google.com
If it makes sense, you can break lines up with \. Make sure there are no spaces after each \.
curl -X POST https://jsonplaceholder.typicode.com/posts \
-d title='Article title' \
-d body='shameless plug' \
--data-urlencode link=https://google.com
Here’s a table to make the commands easier to look up.
| Flag | Purpose |
|---|---|
| -d | Sends data |
| -H | Set request headers |
| -I | View response headers |
| -v | Verbose mode (view request headers, response headers, and body) |
| -u | Basic authentication |
| -X | Sets method |
The flags I taught you above should be enough for most use cases. If you want to find out more about curl, you can read its documentation.