Mastering curl: Essential Command‑Line Options for HTTP Requests

curl is a versatile command‑line tool for performing HTTP requests, acting as a URL client. Its extensive set of options lets you replace graphical tools like Postman for tasks such as setting headers, sending data, handling cookies, and debugging network traffic.

-A (User‑Agent)

Specifies the User-Agent header. The default is curl/[version]. Example:

$ curl -A 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.100 Safari/537.36' https://google.com

Use -A '' to omit the header, or set it via -H 'User-Agent: …'.

-b (Send Cookie)

Sends a Cookie header. Examples:

$ curl -b 'foo=bar' https://google.com

$ curl -b 'foo1=bar' -b 'foo2=baz' https://google.com

$ curl -b cookies.txt https://www.google.com

The last command reads cookies from a local cookies.txt file (created with -c).

-c (Save Cookie)

Writes server‑set cookies to a file:

$ curl -c cookies.txt https://www.google.com

-d (POST Data)

Sends data in a POST request. The Content‑Type header is set to application/x-www-form-urlencoded automatically, and the request method becomes POST, so -X POST can be omitted.

$ curl -d 'login=emma&password=123' -X POST https://google.com/login

$ curl -d '@data.txt' https://google.com/login

--data-urlencode

Like -d but URL‑encodes the data before sending:

$ curl --data-urlencode 'comment=hello world' https://google.com/login

-e (Referer)

Sets the HTTP Referer header:

$ curl -e 'https://google.com?q=example' https://www.example.com

The same effect can be achieved with -H 'Referer: …'.

-F (Multipart Form)

Uploads binary files using multipart/form-data:

$ curl -F '[email protected]' https://google.com/profile

You can specify the MIME type or a different filename:

$ curl -F '[email protected];type=image/png' https://google.com/profile

$ curl -F '[email protected];filename=me.png' https://google.com/profile

-G (GET with Data)

Appends data as a query string to the URL, turning a POST‑style -d into a GET request:

$ curl -G -d 'q=kitties' -d 'count=20' https://google.com/search

-H (Custom Header)

Adds arbitrary HTTP headers:

$ curl -H 'Accept-Language: en-US' https://google.com

$ curl -H 'Content-Type: application/json' -d '{