Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

Development Tools Console Foundations Users and Permissions Creating Users

Zeeshan Dawood
Zeeshan Dawood
7,210 Points

What does curl -L trhou.se/patch01 | bash do? Why did we do it in order to create a new user? I'm just curious.

What does curl -L trhou.se/patch01 | bash do? Why did we do it in order to create a new user? I'm just curious.

1 Answer

William Li
PLUS
William Li
Courses Plus Student 26,867 Points

Hi, Zeeshan Dawood

curl -L trhou.se/patch01 | bash

This command has 2 parts.

  1. the thing to the left of | -- curl -L trhou.se/patch01
  2. and the thing on the right of | -- bash

The | sign on UNIX command line is called pipeline, One of UNIX's design philosophy is "small tool that does one thing really well", and UNIX command line was made up of many of such small tools; and pipeline let you chain 2 or more of these tools together in a single command to do some very powerful thing.

Let's take a look at the 1st part.

curl -L trhou.se/patch01

The URL here trhou.se/patch01 is shorten, upon expanding, you'll see that the full URL http://treehouse-code-samples.s3.amazonaws.com/scripts/console-stage02-patch01.sh points to a .sh file, which is a shell script file.

You can try to just typing curl -L trhou.se/patch01 in the command line, curl gets this file, and display its content as textstream on your console; yeah, that's pretty all it does.

§ curl -L trhou.se/patch01
#!/bin/bash                                                                                                                                                    

echo "==========================================================="                                                                                             
echo "=  We are about to ask for your password                  ="                                                                                             
echo  -e "=  The default password is \033[38;5;81mmike the frog\033[0m                  ="                                                                     
echo "==========================================================="                                                                                             

# This removes the user mike if exists                                                                                                                         

sudo -k                                                                                                                                                        
sudo -- sh -c "/bin/rm -r /home/mike ; /usr/sbin/deluser mike" &> /dev/null                                                                                    

echo "==========================================================="                                                                                             
echo "=  Update Successful !                                    ="                                                                                             
echo "==========================================================="

It's cool that we can just use Command line to get a file from the net and display its content; but that alone isn't very useful, because we're dealing with a shell script file here, script file is supposed be executed.

And that's where the 2nd part of the command kicks in. bash command is used for executing shell script. For example, bash example.sh will execute the example.sh script using the Bash Shell.

So to put everything together. In this command curl -L trhou.se/patch01 | bash.

  1. curl get the script file from the URL
  2. through the power of UNIX pipeline |, the content of the the script file was passed as argument for the bash command to execute line by line.

Hope you find this useful. If you're interested on learning more about UNIX pipeline, check out this page. http://www.maketecheasier.com/pipes-redirection-for-linux-command-line/

Here's also a extremely well-written book on Command Line http://conqueringthecommandline.com/book

thank you for this thorough explanation William Li ! Very helpful :)

William Li
William Li
Courses Plus Student 26,867 Points

Hi, Mary, I'm very glad that you find it helpful :)