Getting Started with cURL

To understand cURL, we should first take a look at what a server is. A server is a powerful computer, software, or virtual machine designed to store, manage, and deliver data, services, or resources to other computers—known as clients—over a network. A server will

• stays online 24/7

• listens on a port

• waits for requests

• sends back responses

In a real-world analogy, a server is like a shop counter:

• You (client) ask something from the shopkeeper

• The shopkeeper checks

• The shopkeeper gives you the thing that you have requested

The internet is just millions of such conversations happening per second.

Problems before cURL existed

To connect to the server, you really need some heavy software like Postman, browsers or you have to write a program.

But what if you just want to:

• Check if a server is alive

• see raw response

• debug quickly

Then cURL came into the picture to solve the problem of displaying raw data on terminals.

What is cURL?

cURL is a tool that allows you to talk to the servers directly from the terminal.

It sends a request to the server same like a browser. The only difference is it doesn’t have any formatting, no UI and no hiddings.

• Browser → need buttons/ui to connect to servers

• cURL → uses terminal commands to connect to the servers

It shows raw responses from the servers.

Why programmers need cURL

Both frontend and backend developers need cURL for various purposes:

Backend developers use cURL to:

• Test endpoints before the frontend exists

• Debug production APIs

• Validate request/response format

• Reproduce bugs

• Check authentication

cURL sits between you and the server:

• Frontend devs use it to test APIs

• Backend devs use it to debug endpoints

• DevOps uses it to check server health

Your first request — what actually happens

Let’s understand what happens when someone sends a request to a server using cURL:

This looks simple, but a LOT happens behind the scenes.

Step-by-step breakdown

1. DNS lookup

   • abc.com → IP address

2. Connection

   • TCP connection to the server

3. TLS handshake (for HTTPS)

   • secure channel established

4. HTTP request sent to the server.

5. Server responds

6. cURL prints the response from the server

Same happen for the Browser in the backend.

Understanding request and response (core idea)

Whenever cURL talks to a server, two things happen:

Request (You → Server)

• What do you want?

• Where do you want it from?

• How do you want it?

Response (Server → You)

• Status (success or error)

• Data (HTML, JSON, text, etc.)

Understanding HTTP Request and Response

An HTTP request is a text-based message sent by a client to a server, such as loading a webpage (GET) or submitting a form (POST).

Key Components of an HTTP Request

• Request Method: Defines the action type

  1. GET to retrieve

  2. POST to send

  3. PUT to update

  4. DELETE to remove.

• Uniform Resource Identifier (URI): The path or address of the resource on the server.

• HTTP Version: (e.g., HTTP/1.1 or HTTP/2).

• Headers: Key-value pairs providing information about the client, content type, or cookies.

• Body: Optional content sent with the request (e.g., form data).

An HTTP response is the data a server sends back to a client after receiving a request containing content like HTML, JS, CSS, images, etc.

Key Components of an HTTP Response

• Status Code: A 3-digit code indicating the success/failures.

• Response Headers: Metadata providing details about the content, content type (e.g., Content-Type: text/html).

• Message Body: The actual content requested by the client, such as HTML code, an image file, or JSON data.

HTTP response status codes:

GET vs POST requests

• Use GET for:

  • Fetching information, such as viewing a webpage, product data, or search data, etc.

  • Operations that are "safe" and do not alter the server's state.

  • Scenarios where users might want to bookmark or share the URL.

• Use POST for:

  • Submitting sensitive data like passwords, login credentials, or personal information.

  • Creating or modifying data on the server, such as posting a comment, registering a new user, or adding an item to a shopping cart.

  • Uploading files.

  • Sending a large amount of data.

Using cURL with APIs (what APIs really are)

An API is just a server that:

• doesn’t return UI

• returns structured data (usually JSON)

So when you do:

curl --request GET \
  --url 'https://api.freeapi.app/api/v1/public/randomjokes?limit=1&query=sciencepage=1' \
  --header 'accept: application/json'

You are:

• calling a server endpoint

• using HTTP GET request

• getting raw data

{"statusCode":200,"data":{"page":1,"limit":1,"totalPages":0,"previousPage":false,
"nextPage":false,"totalItems":0,"currentPageItems":0,"data":[]},
"message":"Random jokes fetched successfully","success":true}

No frontend involved.