Navigating through files and directories

Overview

Teaching: 20 min
Exercises: 10 min

Questions

• What is the directory tree?

• What is a path?

• What happens if I get lost?

• How do I move around?

• How can I see my files and folders?

• How can I use flags?

Objectives

• To gain understanding of the directory tree, and navigate through it as effectively as a GUI interface.

• Explain the similarities and differences between files and directories.

• Gain understanding of relative and actual paths.

• Use options and arguments to change the behaviour of a shell command.

• Demonstrate the usage of tab completion, and explain its advantages.

The directory tree

If you are used to using click and select GUI operations for finding your way through files and folders on your computer, then using the command line to navigate around for the first time is similar to being dropped into a thick maze in the dark without a torch.

In Linux, everything is a file or a process, even directories. In Linux, folders are referred to as directories. A directory is a file itself, one which contains references to other files.

Each file has its own unique ID formed from the file name and a list of directories. This is why it is possible to have different files with the same name in different directories, you have a unique identifier in the file system.

In the same way on Windows and Mac that you select folders and click to go deeper into the file system, Linux has this method to by using what is known as the directory tree. You can see this in action on a Windows machine through the top Search bar, and you can move around the directory tree using the forward and backwards arrow symbols. In Linux however, we need to physically tell the computer where we want to go.

This is what paths are used for. A path is essentially a route that traverses through a directory tree, which each branch and “forks” in the tree separated by the / symbol. This symbol also denotes the root directory, the point at which all directory trees start from. On Windows machines, in the Cmd prgoram, it is denoted with \. The root directory is usually restricted for administrative use. If you are on a desktop, you have access to this root directory. For supercomputers, this is restricted.

Slashes

Notice that there are two meanings for the / character. When it appears at the front of a file or directory name, it refers to the root directory. When it appears inside a path, it’s just a separator.

Let us look at a simple directory structure. This is an important concept to grasp as you move through a file system.

Each of the boxes refers to a directory, and the tree ends at myfile. You can see how the idea of a path arises, so lets add some slashes in here to turn this directory structure into a path.

/home/users/john/Documents/myfile

This is what is known as an absolute path, which refers as the route from the root directory, to the file that we are looking at, being myfile.

However, when we log into a machine, we are never put in the root directory. We are put in the home directory of whoever is using the machine. John is logging on, so naturally he wants to be put where his material is. This is where we introduce the term relative path, which is the path to a file or folder relative to where you are at any time. The relative path in this case is;

john/Documents/myfile

We are in the directory john, and we wish to see the path to my file relative from where we are. Relative paths can be more complex as we stay in one place and try and find a route to other places in our tree. But we will deal with that later, let’s look into our first few exercises.

Locating yourself in a directory tree

Given what you have learned so far, let’s make things a bit trickier with a more complicated tree structure. Put into the chat the following;

1. The absolute path to text.txt
2. The relative path to text.txt if you are in the user1 directory.

Solution

1. /home/users/user1/docs/text.txt
2. ./docs/text.txt

Navigating around

Before we dive into the most commonly used commands for navigation, we should look at a command which creates some empty files we can play around with.

The touch command

This command is not for navigation purposes, but will be useful for generating empty files for us to help with navigation.

By typing touch ABC, we create an empty file called ABC. Here, touch is the command and ABC is the argument we pass to it.

Be careful with whitespace, as if you type touch A B C, it will create 3 files, A, B and C. This is why using underscores (_) or hyphens (-) is often considered best practice.

The command touch A_B_C will therefore create a single file A_B_C.

Create an empty file

Create a single file with a name of your choice. If it has multiple words, separate them with _ or -

The pwd command

One of the most important things to know in Linux at any point is where you actually are. This, thankfully is easy to do in Linux by running a command called pwd (which stands for ‘print working directory’). Remember that directories are like places - at any time while we are using the shell we are in exactly one place, called our current working directory. Directories in Linux are the same as folders. Commands mostly read and write files in the current working directory, i.e. ‘here’, so knowing where you are before running a command is important. pwd shows you where you are:

$ pwd

Your output will depend on where you are. As you are starting out, you are likely going to be placed where your shell considers as “home”. You may have something like this.

/Users/johnsmith

As you get more used to UNIX commands, you will find that you need this command less and less, but for the moment, practice using it whenever you are at any point unsure where you are.

Home Directory Variation

The home directory path will look different on different operating systems. On Linux it may look like /home/johnsmith, and on Windows it will be similar to C:\Documents and Settings\johnsmith or C:\Users\johnsmith (Note that it may look slightly different for different versions of Windows.). In future examples, we’ve used Mac output as the default - Linux and Windows output may differ slightly but should be generally similar.

We will also assume that your pwd command returns your users home directory. If pwd returns something different you may need to navigate there using cd or some commands in this lesson will not work as written. See The cd command for more details on the cd command.

The ls command

We saw this command before in the previous episode, but now lets go into more details. This is one of the most commonly used commands you will get to use.

ls prints the names of the files and directories in the current directory as we saw previously, but we can make its output more comprehensible by using the -F option which tells ls to classify the output by adding a marker to file and directory names to indicate what they are:

• a trailing / indicates that this is a directory
• those with an extension .docx, .c or sometimes no extension are regular files

Depending on your default options, the shell might also use colours to indicate whether each entry is a file or directory, or an executable.

$ ls -F

Applications/ Documents/    Library/      Music/        Public/
Desktop/      Downloads/    Movies/       Pictures/

Let us now use the -a flag as before, which shows all the files in a directory. Now, execute the command below;

$ ls -aF

You may have noticed a big change, with items that may look something like this;

./            ../           .anaconda/    .bash_history/ .ssh/
Applications/ Documents/    Library/      Music/         Public/
Desktop/      Downloads/    Movies/       Pictures/

You can see that some new options have appeared with a . beforehand. These are hidden files or directories which do not appear in normal view. The single . refers to the directory you are currently in. .. on the other hand refers to the directory above the one that you are in. We will look more into details about this as we look into moving around directories.

Let’s say we want to list all the directories that start with the letter D, we can use a handy key called Tab which lists out a bunch of options.

$ ls D

Documents/    Desktop/      Downloads/

Tab can also help autocomplete. Typing the following followed by pressing Tab will autocomplete the word Desktop

$ ls De

Desktop/

The cd command

We next move onto the command that you will use most often, cd which stands for ‘change directory’. This command is akin to double clicking a folder in a graphical interface to get into a folder.

But cd alone isn’t enough, we need to follow it with a directory name to change our working directory.

Let’s say we want to move into our Desktop directory. Using our trick from above with the Tab key will ensure that the directory exists, and will autocomplete.

$ cd Desktop
$ pwd

/Users/johnsmith/Desktop

Note how the present working directory has changed from when we initially used the pwd command. We recommend to use this every time you change directory, like leaving breadcrumbs in the famous Hansel and Gretel story.

Now let’s say we want to go back to where we were. We can do two things. The first is type cd by itself, but this will always put us back in the home directory, regardless of where we call it. It is a handy feature, but can cause you to get lost quickly! The more commonly used way is by referencing our “upper directory” which we covered above.

$ cd ..
$ pwd

/Users/johnsmith

Using this we are back in the directory above where we are

Whitespace matters

For all Linux commands, whitespace is of paramount importance when feeding arguments into a command. Commands like ls-l, and cd.. will not work, and you will get an error saying;

command not found

This error signifies a typo which needs correcting

Practice using cd

Experiment with the cd command and see what happens when you try and use cd along with the following arguments. Don’t forget to use pwd to tell you where you are at any time.

1. ..
2. Nothing
3. .
4. new
5. ../../
6. ~

In the next episode, we will create a number of directories and then practice the cd command with a file structure that we created ourselves.

What works with cd?

Match up the situations below with their expected output. Assume that you are in a directory which contains a single directory, Documents.

Command	Outcome
cd	Moves back one directory
cd.	No such file or directory
cd Desktop	Moves you back two directories
cd ../..	Moves you back into the “home” directory
cd ..	Does nothing, as you are already here
cd Documents	command not found
cd ~	Moves you back into the “home” directory
cd .	Moves you into Desktop

Solution

Command	Outcome
cd	Moves you back into the “home” directory
cd.	command not found
cd Desktop	Moves you into Desktop
cd ../..	Moves you back two directories
cd ..	Moves back one directory
cd Documents	No such file or directory
cd ~	Moves you back into the “home” directory
cd .	Does nothing, as you are already here

Getting help

There are a couple of ways of getting help in Linux for a command, lets take ls as an example

1. We can pass a --help option to the command, such as:

    $ ls --help
   

2. We can read its manual with man, such as:

    $ man ls
   

Depending on your environment you might find that only one of these works (either man or --help, e.g., man works for macOS and --help typically works for Git Bash).

We’ll describe both ways below.

The --help option

Many bash commands, and programs that people have written that can be run from within bash, support a --help option to display more information on how to use the command or program.

$ ls --help

The man command

The other way to learn about ls is to type

$ man ls

The command man is short for manual. This will turn your terminal into a page with a description of the ls command and its options.

To navigate through the man pages, you may use ↑ and ↓ to move line-by-line, or try B and Spacebar to skip up and down by a full page. To search for a character or word in the man pages, use / followed by the character or word you are searching for. Sometimes a search will result in multiple hits. If so, you can move between hits using N (for moving forward) and Shift + N (for moving backward).

To quit the man pages, press Q.

Manual pages on the web

Of course there is a third way to access help for commands: searching the internet via your web browser. When using internet search, including the phrase unix man page in your search query will help to find relevant results.

GNU provides links to its manuals including the core GNU utilities, which covers many commands introduced within this lesson.

The history command

Although not a command for getting help, it is very helpful when typing lots of commands, as one can easily forget what commands you have typed.

$ history

1 pwd
2 ls
3 ls -F
...

The shell stores up to the last 1000 commands, and you can use pipes to search through to find specific commands. We will cover pipes in episode 4.

Key Points

• Information is stored in files, which are stored in directories. A directory is itself a file which contains references to other files.

• The pwd command will always show where you are at any time.

• The ls command lists the contents of the present working directory. Additional options and arguments can filter this list further.

• The man command will return usage and flags of any command you specify

• .. means ‘the directory above the current one’ in the directory tree, whereas . on its own specifies ‘the current directory’.

• The cd command allows you to navigate through directories, but you also need to direct it to where you want to go using cd [path].

• Use history to display recent commands, and ![number] to repeat a command by number.