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Chamal Randika
Chamal Randika

Posted on • Edited on

How to use curl

#linux #api #networking #productivity

What is curl?

curl (connect URL) is a command line tool and a library for transferring data with URLs.

Why you should learn curl?

  1. Test any REST/ GraphQL/ API
  2. Test anything else related to http/https requests and responses.
  3. Test xml/ json RPC protocols
  4. Upload/ download files
  5. Perform Monitoring and deployments with the help of scripts

If you're an engineer of just a pc enthusiast who works with urls, you should learn curl coz it's gonna make your life easier.

Useful curl Flags:

  • -X <method>: Specifies the HTTP method (e.g., GET, POST, PUT, DELETE).
  • -H "<header>": Adds a header to the request.
  • -d "<data>": Sends data with a POST request (useful for sending JSON).
  • -I: Fetches only the HTTP headers.
  • -O: Saves the response to a file.
  • -L: Follows redirects.
  • -u <username>:<password>: For basic authentication.
  • -F "<form-field=@file>": Used to upload files.
  • -v: Enables verbose output to see request/response details.
  • -H "Authorization: Bearer <token>": Adds a Bearer token for authentication.

Examples of Using curl

REST API Example

To make a GET request to a REST API endpoint:

curl -X GET https://api.example.com/users
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To send data with a POST request:

curl -X POST https://api.example.com/login \
-H "Content-Type: application/json" \
-d '{"username": "user", "password": "pass"}'
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GraphQL API Example

To send a query to a GraphQL API:

curl -X POST https://api.example.com/graphql \
-H "Content-Type: application/json" \
-d '{"query": "{ users { id name } }"}'
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To use variables in the query:

curl -X POST https://api.example.com/graphql \
-H "Content-Type: application/json" \
-d '{"query": "query($id: ID!) { user(id: $id) { name } }", "variables": {"id": "123"}}'
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JSON-RPC Example

To call a method in a JSON-RPC API:

curl -X POST https://example.com/api \
-H "Content-Type: application/json" \
-d '{
  "jsonrpc": "2.0",
  "method": "getUser",
  "params": {"id": 1},
  "id": 1
}'
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File Upload Example

To upload a file using curl:

curl -X POST https://example.com/upload \
-F "file=@path/to/file.jpg"
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File Download Example

To download a file and save it locally:

curl -O https://example.com/file.zip
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Testing API with Authentication

For a REST API with Bearer token authentication:

curl -X GET https://api.example.com/protected-resource \
-H "Authorization: Bearer <your-token>"
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Testing API with Basic Authentication

For a REST API with Basic authentication:

curl -u "username:password" https://api.example.com/protected-resource
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Follow Redirects

To make a request and follow any redirects:

curl -L https://example.com
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Get Only HTTP Headers

To retrieve only the HTTP headers of a response:

curl -I https://example.com
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This should be all in one block, ready for you to use. Let me know if you need any more adjustments!
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Curl is more than you think

Believe me when I say this, I cannot cover all of the curl's functionalities from one article.

If I did, it would be book. Infact, there is one if you're curious.

Go ahead and read if you want to know -> Everything about curl

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