curl

Transfer data to/from servers. Essential for testing APIs and debugging HTTP requests.

Synopsis

curl [options] [url]

When to Use It

Use curl when you need to test an API endpoint quickly, inspect HTTP headers, replay a failing request from backend logs, download files in scripts, or verify auth, redirects, and payload formatting outside the browser.

Core Options

-X METHOD

HTTP method (GET, POST, PUT, DELETE).

-H 'Header: Value'

Add custom headers.

-d 'data'

Send data in request body.

-o file

Write output to file.

-I

Fetch response headers only.

-L

Follow redirects.

-u user:pass

Basic auth.

-sS -f

Silent, show errors, fail on HTTP errors.

Usage Examples

GET JSON

Fetch JSON API response.

curl -sS https://api.github.com

POST JSON

Send JSON payload.

curl -X POST -H 'Content-Type: application/json' -d '{"name":"John"}' https://api.example.com/users

Upload File

Send multipart form data.

curl -F 'file=@report.pdf' https://api.example.com/upload

Auth Request

Basic authentication.

curl -u user:pass https://api.example.com/secure

Download with Redirects

Follow 3xx redirects and save file.

curl -L -o app.tar.gz https://example.com/app.tar.gz

Headers Only

Inspect response headers without downloading the full body.

curl -I https://devref.cc

Verbose Debugging

See request and response details while debugging connectivity or TLS.

curl -v https://api.example.com/health

Common Mistakes

  • Forgetting -L on redirected downloads is common and often makes it look like the target file is broken when curl actually saved a redirect response.
  • Many API bugs come from missing Content-Type or Authorization headers, so inspect headers before assuming the server is wrong.
  • When sending JSON, shell quoting mistakes can silently corrupt payloads. Prefer single quotes around the outer body when possible.

Related

HTTP Headers Reference

Understand the headers you are adding and reading in curl requests.

HTTP Methods Cheat Sheet

Pair curl usage with the right GET, POST, PUT, PATCH, and DELETE semantics.

ssh Command Guide

Useful when you need to test remote services from inside a host over shell access.

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