The curl command is going to allow you to transfer data from your hosting over a large number of protocols the server supports. Please do not mistake it with libcurl as both are entirely different things. Libcurl is a development library while curl is a command-line interface tool. To familiarize yourself with a few of curl's options, please read this article. Note that we cannot cover all of the available options as there are over 170 curl command-line flags.
Here is the most basic syntax you should follow when using it:
curl <option> <URL>
First, let's not use any options for our first example and explain what happens in this case:
curl http://www.google.com/
The output is big and unreadable, but basically, what it does is it shows you the content of the website in an HTML format. You are going to receive the same information as when you press the right-click in your browser and then "View page source". A handy feature of curl is the ability to download files from an URL. To do that, you need to add the "-o" option. Please refer to the example below:
curl -o test.zip http://speedtest.tele2.net/10MB.zip
When you type this command, this is the result you are going to receive:
[root@ger1 ~]# curl -o test.zip http://speedtest.tele2.net/10MB.zip
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 10.0M 100 10.0M 0 0 257M 0 --:--:-- --:--:-- --:--:-- 263M
If you do not want to name the file, you are downloading, please use the "-O" (capital o) option:
curl -O http://speedtest.tele2.net/10MB.zip
Another useful application of curl is being able to execute scripts from the command-line interface. This option is great when setting up cron jobs for automating tasks. To do that, please use the "-s" option:
curl -s www.websites.com/script.php
Typically, within the "script.php", you can define a piece of code that clears the cache of your application, generates new RSS feed or performs any task you need once or multiple times a day. The last example we are going to show you using curl is the option to query HTTP headers. You can do that by adding the "-I" flag to the command, followed by the URL:
[root@ger1 home]# curl -I www.google.com HTTP/1.1 200 OK Date: Fri, 13 Mar 2020 10:27:23 GMT Expires: -1 Cache-Control: private, max-age=0 Content-Type: text/html; charset=ISO-8859-1 P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info." Server: gws X-XSS-Protection: 0 X-Frame-Options: SAMEORIGIN Set-Cookie: 1P_JAR=2020-03-13-10; expires=Sun, 12-Apr-2020 10:27:23 GMT; path=/; domain=.google.com; Secure Set-Cookie: NID=200=Upcp-YVD1RGFTiH4MsWWvCz01UbG-nDA4G7k0CjSwmn2KRg9xhbD7nQrMiSq7D1gnvNhflcQrUitPr6wySFMBRiSH3uFDU44sHzGFfD9x_jmE2MHHGWkCKc96SOveanUhu6ldAZ4OChAopGSmebCL5GKFlsKpIJ3D62_soTEuOk; expires=Sat, 12-Sep-2020 10:27:23 GMT; path=/; domain=.google.com; HttpOnly Transfer-Encoding: chunked Accept-Ranges: none Vary: Accept-Encoding
As you can see, this shows you the HTTP response, the date, cache-control, content type, along with other useful information you can use for your applications.
