1. File Navigation and Listing

1.1. Where are we? And what’s in here?

We’ll begin learning how to use the shell with the most basic aspect: knowing where you are in the file system and knowing what files are in there. The pwd command tells you this by printing out the **p**resent **w**orking **d**irectory to the console:

pwd

<output>

The output of this is a path. Think of it as the address in the system. The address it puts out is /home. Just like this suggests, this is your home directory and is the first directory that you are logged in to when you log into the system.

Next, let’s find out what files are there. The ls command will list the files in our current working directory.

ls

<output>

Notice that there is a bunch of stuff here. Some of these things are files and some things are directories. In the Jupyter Lab shell, it colors the directories blue to help you easily tell the difference, but that may not always be the case. We can use the following command to help us determine that:

ls -l

The -l following the ls command is an optional argument that tells ls to output the directory contents in a **l**ong format. Notice the output here:

drwxrwxr-x 26 ubuntu ubuntu 4096 Nov  9 16:43 anaconda3
drwxrwxr-x  6 ubuntu ubuntu 4096 Nov 16 04:33 blast_crash_course
drwxrwxr-x  2 ubuntu ubuntu 4096 Nov  9 16:44 certs
-rw-rw-r--  1 ubuntu ubuntu    0 Nov 16 04:35 something

The contents of each of the columns are:

Column	Value
1	File permissions
2	File size (in memory blocks)
3	File owner
4	Owner group
5	File size (in bytes)
6	Creation date
7	File or directory name

All of this is useful information, but all we’re concerned with right now is the file permissions. The d in the front of this string tells us that the object we’re looking at is a directory.

Typing ls by itself will display the contents of your current directory. You can also type the name of another directory to list its contents. Let’s take a look at the blast-crash-course directory:

ls blast-crash-course

Now let’s move into the directory. The cd command changes the present working directory to the directory that you enter. For example, to move into the blast_crash_course directory, we would type:

cd blast-crash-course

We looked at the contents of this directory from our home directory just before we did the cd command, but let’s do it again for practice:

ls

Let’s move into the materials folder:

cd materials

Now that we’re here, let’s ls again so we know what’s in here:

ls

And let’s move into the shell-tutorial folder…

cd shell-tutorial

…and ls again:

ls

Get used to using ls a lot - when you’re working with your data and moving between directories frequently, you’re going to frequently use ls to remind yourself what’s in each folder. I personally just hit ls whenever I move into a new directory.

There are also some shorthand ways to maneuver around the file system using cd. For example, we can move to our home directory by using the ~ character:

cd ~

Using the pwd command will show you that we’re back in the home directory. Similarly, using the - character will move us to the last directory we were at:

cd -

We can also move up one directory with ..:

cd ..

Do you remember where we are now? Use pwd to remind yourself.

We can also pass the .. argument to ls to see what’s in the directory above our current one:

ls ..

See the table below for a reference for the different cd arguments:

cd argument	Meaning
.	This directory
..	The directory above this directory
-	The last directory
	Home directory
~	Home directory
/	Root directory

So far, we’ve been using cd change directories one step at a time. However, we can change directories more than one step at a time by just typing out the full path. For example, let’s go back to our home directory…

cd ~

…and navigate to the shell-tutorial folder in one cd command.

cd blast_crash_course/materials/shell-tutorial

Note that you don’t have to type out the full name of each of the directories. If you start typing the name of a file and press tab, shell will attempt to autocomplete the name for you. So, to complete the above command using tab completion, you can type:

cd blast<tab>mat<tab>shell<tab>

We can combine this with the special cd options we learned before. For example, let’s take a look at what’s in the directory above shell-tutorial:

ls ..

If we wanted to move to the blast-tutorial directory, we can type:

cd ../blast-tutorial

Nice!

1.1.1. Exercises

• List the contents of your home directory. (Hint: use one of the special characters from the table above)