Skip to content

Latest commit

 

History

History
126 lines (108 loc) · 5.33 KB

cURL.md

File metadata and controls

126 lines (108 loc) · 5.33 KB

cURL COMMAND

  • cURL is a computer software project providing a library and command-line tool for transferring data using various network protocols. The name stands for "Client URL"

INSTALLATION OF cURL :

  • cURL can be installed using the following command
sudo apt install curl

Getting started with cURL :

  • Accept Requests send by the server :

    • In all of the below examples, the request is sent using the 'GET' method of http request and are just focusing on the response we get from the server.
    NOTE: cURL command when executed will return the body of the response sent by the server
    fiesta@fiesta-VirtualBox:~/Desktop$ curl https://www.example.com
<!doctype html>
<html>
<head>
  <title>Example Domain</title>
  <meta charset="utf-8" />
  <meta http-equiv="Content-type" content="text/html; charset=utf-8" />
....
    NOTE: '--head' option will display only the head of the response
    fiesta@fiesta-VirtualBox:~/Desktop$ curl --head http://www.example.com
HTTP/1.1 200 OK
Accept-Ranges: bytes
Age: 413251
Cache-Control: max-age=604800
Content-Type: text/html; charset=UTF-8
D ate: Tue, 11 Feb 2020 09:55:06 GMT
Etag: "3147526947"
Expires: Tue, 18 Feb 2020 09:55:06 GMT
Last-Modified: Thu, 17 Oct 2019 07:18:26 GMT
Server: ECS (nyb/1D13)
X-Cache: HIT
Content-Length: 1256

fiesta@fiesta-VirtualBox:~/Desktop$
    NOTE: '-o' option is used to save the response in a file
    fiesta@fiesta-VirtualBox:~/Desktop$ curl -o output.txt http://www.example.com
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  1256  100  1256    0     0    437      0  0:00:02  0:00:02 --:--:--   437
fiesta@fiesta-VirtualBox:~/Desktop$ cat output.txt
<!doctype html>
<html>
<head>
    <title>Example Domain</title>
    <meta charset="utf-8" />
    <meta http-equiv="Content-type" content="text/html; charset=utf-8" />
....
    NOTE: '-O' will download the response file,as in the example it downloads the manual.html file
    fiesta@fiesta-VirtualBox:~/Desktop$ ls
output.txt
fiesta@fiesta-VirtualBox:~/Desktop$ curl -O https://curl.haxx.se/docs/manual.html
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 44194  100 44194    0     0   9781      0  0:00:04  0:00:04 --:--:--  9783
fiesta@fiesta-VirtualBox:~/Desktop$ ls
manual.html  output.txt
fiesta@fiesta-VirtualBox:~/Desktop$ cat manual.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head> <TITLE>curl - Tutorial</TITLE>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
<link rel="stylesheet" type="text/css" href="https://curl.haxx.se/curl.css">
.....
    NOTE: multiple URLs can we entered in the single commands
    fiesta@fiesta-VirtualBox:~$ curl https://www.example.com https://www.google.com
<!doctype html>
<html>
    <head> <TITLE>curl - Tutorial</TITLE>
.....

Sending POST request :

  • As we have seen previous topic examples, when http requests are sent using 'GET' method, it is used to only to retrieve information from the given server using a given URL. Requests using GET would only retrieve data and should have no other effect on the data stored in the server.

  • But when we send the a http request using the 'POST' method, this means that we are trying to send the data from our side i.e client side to the server side for example "search options" or "login information"

For example :

Simple login page

Let's consider that the above login page has the following HTML code
<form method="POST" action="junk.cgi">
  <h1> Login Page </h1>
  <text>Username:</text>
  <input type=text name="username">
  <text>Password:</text>
  <input type=text name="password">
  <input type=submit name=press value=" Login ">
</form>
NOTE : In order to send a 'POST' request we will have to send the values of username and password. We can use the option '--data' in order to send the required data, as shown before.
NOTE : 'username' and 'password' is the name for the input box, and these names can be known by seeing the html code of the website.
fiesta@fiesta-VirtualBox:~$ curl --data "username=admin&password=admin" http://www.stealmylogin.com/demo.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>

....