Linux: navigating the system

Where are we?

The command pwd stands for Print Working Directory and it will print the complete path to our current directory:

username@bash:~$ pwd  
/home/username

This is your home directory. In Linux systems, each user has its own home directories, where they will be saving their own files.

Creating a directory

You can create a directory using the command mkdir (which stands for Make Directory):

username@bash:~$ mkdir linux_tutorial 

By default, the command mkdir creates directories inside our current working directory, which in our case is /home/username. However we can use mkdir to create a directory in any other location.

Let’s suppose we wanted to create a directory called linux_tutorial_subdirectory inside our linux_tutorial directory:

username@bash:~$ mkdir linux_tutorial/linux_tutorial_subdirectory 

What’s in our current directory?

Now let’s inspect the content of our directories. For that we will use the command ls, which prints all files and folders located in our current directory:

username@bash:~$ ls  
linux_tutorial

If we want to print the content of a directory other than our current one, we need to give its path as an argument to ls. Let’s check what is inside linux_tutorial:

username@bash:~$ ls linux_tutorial  
linux_tutorial_subdirectory 

If we want ls to print more information, we can use some of its options. For instance, option -l can print information on user permissions over that object, as well as its size and last modification date:

username@bash:~$ ls -l linux_tutorial
drwxrwxr-x 2 bioma bioma 4096 out 23 09:52 linux_tutorial_subdirectory

Our last command has printed file sizes in bytes. For most cases we will want that in a human-readable format, what can be achieved by adding the -h option:

username@bash:~$ ls -lh linux_tutorial
drwxrwxr-x 2 bioma bioma 4,0K out 23 09:52 linux_tutorial_subdirectory

Moving around

The command cd (which stands for Change Directory) allows us to move to another directory. Its syntax is straightforward since it only takes one argument, which is the target directory we want to move to:

username@bash:~$ cd linux_tutorial  
username@bash:~$ pwd  
/home/username/linux_tutorial

Absolute vs relative paths

In the last command we used cd to move to the linux_tutorial directory. Notice that the absolute path to linux_tutorial is /home/username/linux_tutorial. However, we didn’t need to inform the whole path to cd because it is capable of understanding what we call relative paths.

The idea behind relative paths is that cd knows what our current directory is (in this case, we were at /home/username) and uses it as a reference. Then when we call cd informing linux_tutorial as a relative path, the command will move to a directory called linux_tutorial inside /home/username.

While absolute paths start with a forward slash (/), relative paths don’t.

Of couse the cd command would also have worked if we had used an absolute path instead:

username@bash:~$ cd /home/username/linux_tutorial
username@bash:~$ pwd  
/home/username/linux_tutorial

Attention
The cd command was used as an example to explain the concept behind relative paths. However, any other command in the terminal should understand them.

Shortcuts that will make your life easier

If you want to go back to the previous (parent) directory, you don’t need to specify its complete path. The shortcut .. will do that for you:

username@bash:~$ cd ..  
username@bash:~$ pwd  
/home/username

You can even concatenate multiple ..:

username@bash:~$ cd ../..  
username@bash:~$ pwd  
/

Now we are in the so called root directory. This is the top of the hierarchical structure of the system. All other directories are actually subdirectories of it.

Another possibly useful shortcut is ~, which represents the home directory of your user:

username@bash:~$ cd ~  
username@bash:~$ pwd  
/home/username

Attention 2 The shortcuts .. and ~ work with any other commands (not only cd):

username@bash:~$ ls ~  
linux_tutorial

The tab completion trick

Typing out long paths can be tedious and slow, without mentioning the chances of typing errors (typos). However, the command line have a powerfull mechanism to help us with that: it’s called tab completion.

The idea is that whenever you start typing a path, if you hit the Tab key on your keyboard the command line will invoke an autocompletion action. It nothing happens, it means there are several possibilities for autocompletion. In that case you should hit Tab again to show all the possibilites, continue typing and then hit Tab again to continue the autocompletion process. Try it yourself to seed the power of tab completion!