Overview

Teaching: 15 min
Exercises: 0 min

Questions

• How can I move files around?

• How can I see what files and directories I have?

• How can I specify the location of a file or directory on my computer?

Objectives

• Explain the similarities and differences between a file and a directory.

• Translate an absolute path into a relative path and vice versa.

• Construct absolute and relative paths that identify specific files and directories.

Navigation

The part of the operating system responsible for managing files and directories is called the file system. It organizes our data into files, which hold information, and directories (also called “folders”), which hold files or other directories.

You need to be able to navigate without a Graphical User Interface (GUI). Unix file systems are trees with the roots at the top:

The first command that we will look at is called pwd (print working directory). Let’s type it in your VSCode Terminal once logged in:

$ pwd

Now let’s download the sample data from here using wget command:

$ wget https://swcarpentry.github.io/shell-novice/data/shell-lesson-data.zip

Once downloaded the zip file to your home directory on SuperPOD, you can unzip it using command unzip:

$ unzip shell-lesson-data.zip

We can see what’s in our the downloaded directory by running command ls, which stands for “listing”:

$ ls shell-lesson-data

Tips: you can try the feature called Auto completion in linux using Tab button by typying:

$ ls sh (tab)

Now let change the current prompt into the folder that just unzipped using cd command:

$ cd shell-lesson-data

ls prints the names of the files and directories in the current directory in alphabetical order, arranged neatly into columns. We can make its output more comprehensible by using the flag -F, which tells ls to add a trailing / to the names of directories:

$ ls -F

And note that there is a space between ls and -F: without it, the shell thinks we’re trying to run a command called ls-F, which doesn’t exist.

Now let try ls -l stands for long listing, we check the content of the folder named exercise-data:

$ ls -l exercise-data/

ls has lots of other options. To find out what they are, we can type:

$ ls --help

For more information on how to use ls we can type man ls. man is the Unix “manual” command: it prints a description of a command and its options, and (if you’re lucky) provides a few examples of how to use it.

$ man ls

To navigate through the man pages, you may use the up and down arrow keys to move line-by-line, or try the “b” and spacebar keys to skip up and down by full page. Quit the man pages by typing “q”.

We can also use ls to see the contents of a different directory. Let’s list the directories of all the SuperPOD users (note that you cannot actually go inside other people’s directories):

$ ls /home

Note that on SuperPOD you cannot access other people’s directories.

Other Hidden Files

In addition to the hidden directories .. and ., you may also see a file called .bash_profile. This file usually contains shell configuration settings. You may also see other files and directories beginning with .. These are usually files and directories that are used to configure different programs on your computer. The prefix . is used to prevent these configuration files from cluttering the terminal when a standard ls command is used.

These are the basic commands for navigating the filesystem on your computer: pwd, ls and cd. Let’s explore some variations on those commands. What happens if you type cd on its own, without giving a directory?

$ cd

How can you check what happened? pwd gives us the answer!

$ pwd

It turns out that cd without an argument will return you to your home directory, which is great if you’ve gotten lost in your own filesystem.

If we want to move up one level from the shell directory, we could use cd ... But there is another way to move to any directory, regardless of your current location.

Few More Shortcuts

The shell interprets the character ~ (tilde) at the start of a path to mean “the current user’s home directory”. For example, ~/shell-lesson-data is equivalent to /users/<your SuperPOD username>/shell-lesson-data.

In addition, you can also use $HOME as the shortcut to your home directory:

Another shortcut is the - (dash) character. cd will translate - into the previous directory I was in, which is faster than having to remember, then type, the full path. This is a very efficient way of moving back and forth between directories. The difference between cd .. and cd - is that the former brings you up, while the latter brings you back.

Key Points

• The file system is responsible for managing information on the disk.

• Information is stored in files, which are stored in directories (folders).

• Directories can also store other directories, which forms a directory tree.

• cd path changes the current working directory.

• ls path prints a listing of a specific file or directory; ls on its own lists the current working directory.

• pwd prints the user’s current working directory.

• whoami shows the user’s current identity.

• / on its own is the root directory of the whole file system.

• A relative path specifies a location starting from the current location.

• An absolute path specifies a location from the root of the file system.

• ’..’ means ‘the directory above the current one’; ‘.’ on its own means ‘the current directory’.