The Unix filesystem

Bash allows to give instructions to a Unix operating system. The first thing we need to know is how storage is organized on such as system.

Structure

The Unix filesystem is a rooted tree of directories. The root is denoted by /.

Several directories exist under the root. Here are a few:

• /bin     This is where binaries are stored.
• /boot    There, you can find the files necessary for booting the system.
• /home    This directory contains all the users home directories.

These directories in turn can contain other directories. /home for instance contains the directories:

• /home/user001
• /home/user002
• /home/user003
• …

The home directory of each user contain in turns many files and directories.

Navigation

Working directory

The current working directory can be obtained with:

pwd       # print working directory

Your turn:

What is your current working directory?

Changing directory

To navigate to another directory, you use cd (change directory) followed by the path of the directory.

Example:

cd /home

Because /home was the parent directory (one level above in the rooted tree) of our working directory, we could have also navigated there with cd .. — the two dots represent one level up (a single dot represents the working directory).

Your turn:

• What do you think will happens if you run cd .. from /home?
• What do you think will happens if you run cd . from /home?

From any location, you can always go back to your home directory (e.g. /home/user009) by running cd without argument. Alternatively, you can use cd ~. This is because ~ gets expanded by the shell into the path of your home. Finally, you can use cd $HOME. $HOME is an environment variable representing the path of your home.

Your turn:

Try using cd - (that’s the minus sign) a few times. What does this command do?

Absolute and relative paths

Absolute paths give the full path from the root (e.g. /bin, /home/user009/file).

Relative paths give the path relative to the working directory (e.g. ../dir/file, dir)

Your turn:

Is ~ an absolute or relative path?

Creating files and directories

Files can be created with a text editor:

nano newfile.txt

The file actually gets created when you save it from within the text editor.

or with the command touch:

touch newfile.txt

This creates an empty file.

touch can create multiple files at once:

touch file1 file2 file3

New directories can be created with mkdir. This command can also accept multiple arguments to create multiple directories at once:

mkdir dir1 dir2

Deleting

Files can be deleted with rm.

Directories can be deleted with rm -r (recursive) or, if they are empty, with rmdir.

Be careful that these commands are irreversible.

Copying, moving, and renaming

Copying is done with the cp command. Moving and renaming with the mv command.

Your turn:

Why is there only one command to move and rename?