Let’s Have a Limited Look at Linux’s cURL Application

This article is going to be a limited look at cURL, a Linux application used in the terminal to transfer data. cURL is a very extensive program and we’ll just be scratching the surface. You’ll see why we’re just scratching the surface soon enough. It’s a very comprehensive application.

So, what is cURL? It’s an application that you use in your terminal to transfer data. However, as said, it’s an insanely complicated program. We’re just barely going to scratch the surface. Let’s start with the definition.

First, ‘man curl’ defines itself nice and easily:

curl – transfer a URL

However, if you keep reading to find the description, you’ll find this gem:

curl is a tool to transfer data from or to a server, using one of the supported protocols (DICT, FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET and TFTP). The command is designed to work without user interaction.

curl offers a busload of useful tricks like proxy support, user authentication, FTP upload, HTTP post, SSL connections, cookies, file transfer resume, Metalink, and more. As you will see below, the number of features will make your head spin!

Yeah… 

In fact, while we’re here, why don’t you have a look at the man page for cURL. Really, click that link! I think that may be one of the longest man pages out there. cURL was originally released in 1997 and appears to have picked up everything along the way.

We’ll just be going over installing it and a couple of ways you can get started using it. To learn more, read the man page!

Using cURL:

There’s some chance that it didn’t come installed with your distro’s basic installation, so let’s first cover some ways of installing it. It’s sure to be in your default repositories for any major distro, and will almost certainly be trivial to install.

Open your terminal by pressing CTRL + ALT + T and use the correct following command to install it:

Debian/Ubuntu/Derivatives:

sudo apt install curl

OpenSUSE/Derivatives:

sudo zypper install curl

RHEL/Fedora/Derivatives:

sudo yum install curl

Arch/Derivatives:

sudo pacman -Sy curl

If your distro isn’t listed above, read the documentation for your distro’s package manager. If it’s not available, you can always build it from source. The project’s homepage can be found here.

With cURL now installed, and your terminal still open, you can test it easily enough. First, try this command:

curl https://linux-tips.us/temp/sample.txt

That should give you a nice message. It’ll appear in your terminal and that’s it. When you close the terminal window, the message will be gone. So, what if you want to download it? For that, you use the -O switch. Let’s try something:

cd Downloads
mkdir temp
cd temp
curl -O https://linux-tips.us/temp/sample.txt

That will make ‘sample.txt’ download to that directory. It’s not entirely unlike wget in those regards. If you want to change the name of the fetched file, you use the -o switch and the new name. So, the above code would look like this:

cd Downloads
mkdir temp
cd temp
curl -o example.txt https://linux-tips.us/temp/sample.txt

That will save sample.txt as example.txt and both of those commands will show you the transfer’s progress. This specific file isn’t large enough for that to really matter, but it’s noteworthy that it does so for future transfers.

Those are just a couple of ways to use cURL, and that’s it. It’s seriously powerful and flexible. You can read the man page and learn more about it, as it is a tool we should all have in our toolboxes. It’s useful in many situations and is worth spending some time to learn more about it. 

Closure:

There’s another article in the books! As mentioned, it’s just a very limited look at cURL. To do a full tutorial would take days and days worth of articles and I’m much happier just exposing new users to the basic functionality. Even if you already have it installed and know how to use it, be sure to curl the sample.txt!

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