The command line

Terminal

The picture above shows a terminal window where I am logged into Kebnekaise (from my desktop defiant).

The command line is an interface for typing commands directly to a computer’s operating system. It is a user interface that is navigated only with the keyboard, by typing commands at a prompt, instead of by clicking with a mouse or similar.

The Command Line Interface (CLI) is available in all operating systems, including Windows, Linux and macOS, but it is most commonly associated with Linux.

Note

In Unix or Linux, the prompt may be shown as $, % or > depending on the shell.

The opposite of a CLI is a GUI (Graphical User Interface), which generally uses a mouse or similar for navigating.

Command line interfaces often gives access to many more capabilities than the graphical user interface does, and it is also practical and normally faster in situations where you login with a terminal on a remote system, like Tetralith, or Kebnekaise as I did above.

Warning

You will find that many/most commands in this course are prefaced with either $ or [x_birbr@tetralith1 ~]$, or something like [x_birbr@tetralith1 x_birbr]$.

This is the prompt from the computer system, where $ just is the default (bash) prompt, and the others are an example of a prompt you would see when logged into a compute cluster (in this case Tetralith - my home directory versus my project storage directory.

You can see an example of such a prompt in the picture a bit further up on the page, though that is from where I am logged into “Kebnekaise” from my computer “defiant”.

Do NOT copy this prompt if you are copying code snippets. It should not be included in the command.

Exercise: Open a terminal

Do one of the following:

  1. Tetralith
    • Use an SSH client of your choice or ThinLinc
    • Log in with your USERNAME: 
      ssh USERNAME@tetralith.nsc.liu.se
    • If you logged in with ThinLinc, open a terminal
  2. Any other HPC system of your choice
  3. Open a terminal on your own computer

Code-along: try a few commands

NOTE: These commands will all be described in more details in the next section about Navigating the File System

List some files and directories: 

ls

Create a file: 

touch MYFILE.txt

Create a directory: 

mkdir MYDIR

List your files and directories again: 

ls