Karan Sharma

Ramblings on tech, cycling, and finance

cURL

Show only headers

curl has an option to display only headers using -I. This flag is better than using a combination of -s and redirecting the output to /dev/null or 2>&1 as it's easier to remember.

An important thing to note is that -I sends a HEAD request. As shown here:

$ curl -I  -vvvv https://mrkaran.dev 2>&1 | grep -C 3 'HEAD'
} [5 bytes data]
* Using Stream ID: 1 (easy handle 0x55dff1e30920)
} [5 bytes data]
> HEAD / HTTP/2
> Host: mrkaran.dev
> user-agent: curl/7.76.1
> accept: */*

However it's easy to override the HTTP method using -X. For eg, to send a GET request but only display the headers:

curl -I -X GET -vvvv https://mrkaran.dev

Send a JSON payload from file

curl -i -XPOST -H "Content-Type: application/json" -d @mock_payload.json http://localhost:6000/endpoint

Fail if response is 4xx/5xx

Using the --fail flag, curl can detect if the response code is an error (includes 4xx,5xx with an exception for 401 and 407 as they are authentication related). This is handy to use in scripts. Read this for more.

❯ curl -i --fail https://httpbin.org/status/200
HTTP/2 200 
date: Tue, 02 Nov 2021 10:43:38 GMT
content-type: text/html; charset=utf-8
content-length: 0
server: gunicorn/19.9.0
access-control-allow-origin: *
access-control-allow-credentials: true

❯ curl -i --fail https://httpbin.org/status/502
curl: (22) The requested URL returned error: 502 

❯ curl -i --fail https://httpbin.org/status/400
curl: (22) The requested URL returned error: 400