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🔹 What is curl?

curl stands for Client URL.

It is a command-line tool used to send requests to URLs and get responses from servers.

👉 In simple words:

curl is used to talk to servers from the terminal

You can:

• Call APIs (REST APIs)
• Download files
• Upload files
• Send GET, POST, PUT, DELETE requests
• Send headers, tokens, cookies
• Test backend APIs (Django, Spring Boot, Node, etc.)

🔹 Where is curl used?

• Backend developers (API testing)
• DevOps (health checks, automation)
• Cloud engineers (AWS, servers)
• CI/CD pipelines
• Debugging production APIs

🔹 Is curl installed by default?

Check:

curl --version

🔹 Basic curl syntax

curl [options] URL

Example:

curl https://example.com

👉 This sends a GET request to the server.

🔹 HTTP Methods in curl

🔹 GET Request (Most common)

curl https://api.example.com/users

With query params:

curl "https://api.example.com/users?id=10"

🔹 Show full response (headers + body)

curl -i https://example.com

🔹 Show only headers

curl -I https://example.com

🔹 Pretty print JSON response

curl https://api.example.com/users | jq

(jq is a JSON formatter tool)

🔹 POST Request (Send data)

Send JSON data

curl -X POST https://api.example.com/users \
-H "Content-Type: application/json" \
-d '{"name":"Dev","age":22}'

Explanation:

• -X POST → HTTP method
• -H → Header
• -d → Data (body)

🔹 PUT Request (Update)

curl -X PUT https://api.example.com/users/1 \
-H "Content-Type: application/json" \
-d '{"name":"Dev","age":23}'

🔹 PATCH Request (Partial update)

curl -X PATCH https://api.example.com/users/1 \
-H "Content-Type: application/json" \
-d '{"age":24}'

🔹 DELETE Request

curl -X DELETE https://api.example.com/users/1

🔹 Sending Headers (Auth tokens, etc.)

curl https://api.example.com/profile \
-H "Authorization: Bearer YOUR_TOKEN"

Multiple headers:

curl https://api.example.com \
-H "Accept: application/json" \
-H "User-Agent: curl-test"

🔹 Authentication with curl

Basic Auth

curl -u username:password https://api.example.com

Bearer Token

curl -H "Authorization: Bearer TOKEN" https://api.example.com

🔹 Upload file using curl

curl -X POST https://api.example.com/upload \
-F "file=@image.png"

🔹 Download file using curl

curl -O https://example.com/file.zip

Rename file:

curl -o myfile.zip https://example.com/file.zip

🔹 Follow redirects

curl -L https://short.url

🔹 Save response to file

curl https://api.example.com/data -o data.json

🔹 Timeout in curl

curl --max-time 10 https://example.com

🔹 Silent mode (no progress)

curl -s https://example.com

🔹 Verbose / Debug mode (VERY IMPORTANT)

curl -v https://example.com

👉 Shows:

• DNS lookup
• TLS handshake
• Request headers
• Response headers

🔹 Common curl options (Must know)

🔹 curl vs Postman

👉 In real projects, both are used

🔹 curl in Backend Development (Your case)

Since you work with Django APIs & Angular, curl is useful for:

• Testing API endpoints without frontend
• Checking auth headers
• Debugging POST/GET issues
• Server health checks on EC2

Example for Django:

curl http://127.0.0.1:8000/api/expenses/

🔹 Common curl mistakes ❌

1. Forgetting quotes around JSON
2. Missing Content-Type
3. Wrong HTTP method
4. Sending GET with -d
5. Forgetting -L for redirects

🔹 Interview-ready answer

Q: What is curl?

curl is a command-line tool used to transfer data between a client and a server using protocols like HTTP, HTTPS, FTP, etc. It is commonly used for testing APIs, downloading/uploading files, and debugging network requests.

🔹 When should you use curl?

• When you don’t have frontend
• When debugging APIs on server
• When automating API calls
• When Postman is not available