Getting Started with cURL

Before we talk about what cURL or curl lets discuss what a server is**,** and why we need it

In simple terms, a server is a computer or system that provides data, services, or programs to clients. Servers receive requests from clients to retrieve files or data stored (e.g., in a database). Like your computer, a server has an operating system—such as Ubuntu, Windows, etc.

Types of Servers

• Web Servers — Deliver web content (HTML, CSS, JS, images).

• File Servers — Store and manage files.

• Mail Servers — Handle incoming and outgoing emails.

• Database Servers — Manage databases and applications.

Types of Servers

• Web Servers - Deliver web contents

• File Servers - Store and Manage files

• Mail Servers - Handles incoming & outgoing mails

• Database Servers - Manage databases and applications.

What is cURL? (In Very Simple Terms)

cURL is an open-source command-line tool and library that lets you transfer data using various network protocols (HTTP, HTTPS, FTP, and more). It’s often used to:

• Interact with APIs

• Download files

• Test how a server responds

cURL stands for Client URL — you (the client) use it to talk to a URL (a server).

How cURL Sends Messages to a Server

cURL builds an HTTP request and sends it to a specific URL. It handles the full request–response cycle in the terminal—no browser or UI needed.

curl https://shivam-goyal.site

Key Components of a cURL Message

1. URL: The destination server address (e.g., https://shivam-goyal.site).

2. HTTP Method (-X): Defines the action (e.g., GET, POST, PUT, DELETE). If not specified, it defaults to GET.

3. Headers (-H): Metadata about the request, such as Content-Type (e.g., -H "Content-Type: application/json").

4. Body (-d): The message data itself. Used with POST our PUT methods.

What just happened?

1. cURL sent a GET request to https://shivam-goyal.site.

2. The server at that URL processed the request.

3. The server sent back a response (status + headers + body).

4. cURL printed the body (the HTML) to your terminal.

Understanding Request and Response

Every HTTP exchange has two parts: request (what you send) and response (what the server sends back).

The Response

When you run curl https://shivam-goyal.site, you mainly see the body. But the full response also includes:

1. Status code — A number that tells you if the request succeeded or failed.

• 200 — OK (success).

• 404 — Not Found.

• 500 — Server error.

2. Headers — Metadata (content type, date, etc.).

3. Body — The actual data (HTML, JSON, etc.).

To see status and headers as well, use -i (include headers):

curl -i https://shivam-goyal.site

You’ll see something like:

HTTP/2 200

content-type: text/html; charset=UTF-8

Then the HTML follows. 200 means the request succeeded.

GET vs POST (Only These Two for Now)

• GET — “Give me data.” Used to read or fetch something. Nobody needed. Default in cURL.

• Example: open a URL, fetch a user, list items.

POST — “Here is some data; do something with it.” Used to send data to the server (e.g., create a user, submit a form).

• You often send a body (e.g., JSON) and set Content-Type.

GET (default)

curl https://api.shivam-goyak.site/users

Same as:

curl -X GET https://api.shivam-goyal.site/users

POST (sending data)

curl -X POST https://api.shivam-goyal.site/users \

  -H "Content-Type: application/json" \

  -d '{"name":"Alice","email":"alice@example.com"}'

- -X POST — use POST method.

- -H "Content-Type: application/json" — body is JSON.

- -d '...' — the JSON body.

Stick to GET and POST at first; add PUT/DELETE later when you’re comfortable.

Using cURL to Talk to APIs

Many services expose APIs—URLs that return or accept data (often JSON) instead of a full webpage.

1. Read the API docs — They tell you the URL, method (GET/POST), and whether you need headers or a body.

2. Start with GET — Try fetching a public API:

   curl https://jsonplaceholder.typicode.com/posts/1

You’ll get JSON for “post” with id 1.

3. Then try POST — Same site allows a sample POST:

curl -X POST https://jsonplaceholder.typicode.com/posts \
     -H "Content-Type: application/json" \
     -d '{"title":"Hello","body":"My first post","userId":1}'

That’s the core idea: same tool (cURL), different URLs and methods — you’re “talking” to the API from the terminal.

Common Mistakes Beginners Make with cURL

1. Forgetting quotes — If the URL or JSON has &, ?, or spaces, put it in quotes:

 curl "https://example.com?name=John Doe"

2. Wrong Content-Type for POST — If you send JSON, set the header:

  -H "Content-Type: application/json"

3. Typos in the URL — http vs https, missing slash, wrong domain. Double-check the URL.

4. Using GET when you need POST — Creating or updating data usually needs POST (or PUT). Check the API docs.

5. Ignoring the status code — Always look at the first line of the response (e.g., HTTP/2 200 or 404). Use curl -i to see it.

Start with simple commands; add flags only when you need them.

Where cURL Fits in Backend Development

• Backend dev — You build the server. cURL lets you call your own APIs (GET/POST) without a frontend.

• Testing — Quick checks: “Does this endpoint return 200? What JSON do I get?”

• Scripts — Cron jobs, deploy scripts, or automation that hit a URL.

• Learning — You see the raw HTTP request and response, which helps when you use libraries (e.g., fetch, Axios) in code.

Conceptually, Browser and cURL both send HTTP requests; the browser also renders HTML and runs JS. cURL just shows you the “wire” — the request and response — which is why it’s so useful for APIs and debugging.