Ubuntu Linux for Robotics · Lesson 04 of 96

Navigating: pwd, ls and cd

Where am I, what is here, and how to move; absolute and relative paths, and tab completion.

Estimated time · 30–45 min

Learning goals

What you will understand

Explain navigating: pwd, ls and cd in your own words
Use it in a small workstation example
Verify the result instead of assuming it worked

Understand the idea first

The mental model

pwd prints the current (working) directory, ls lists a folder, and cd changes it. An absolute path starts with / and works from anywhere; a relative path starts from where you are. . is the current folder, .. is the parent, ~ is your home, and cd - returns to the previous folder.

Use the Tab key to complete names and the Up arrow to recall commands; they prevent typos. ls -l shows details, ls -a shows hidden files and ls -lh shows sizes in readable units. Read what a command printed before running the next one.

Guided lesson

Work through these steps

1.
Open a terminal and record the current state before changing anything.
2.
Read the navigating: pwd, ls and cd commands and predict what each one does.
3.
Run the commands one at a time and compare each output with your prediction.
4.
Write the commands that worked in a setup note you can repeat later.

Worked example

Read it before you run it

pwd
# Print the folder you are in.
cd /usr/share
# Go to an absolute path.
cd ..
# Go up one level, to /usr.
cd ~
# Go to your home directory.
ls -lah
# List everything, including hidden files, with sizes and permissions.
cd -
# Return to the folder you were in before.

What the example is doing

1.Lines without sudo only inspect or change files you own; sudo authorizes a system-wide change.
2.Read command output before moving to the next line. Stop if names, versions, disks, or paths differ from the lesson.
3.Comments beginning with # explain safety checks and are not executed by the shell.

Watch it run · The robot's computer

See what this code does

The terminal types this lesson's practice solution and runs it. The scene shows the kind of robot behaviour that code drives. It plays by itself and loops.

Practice code

Now type it yourself

Open a terminal, run the starter line by line (or save it as practice.sh and run bash practice.sh), and replace every TODO with your own command.

# TODO: change to /usr/share with cd and print the working directory

Expected output

/usr/share

Stuck? Show the full solution (try it yourself first)

cd /usr/share
pwd

Expected result

How you know it worked

Each command completes without an unexplained error.
Your notes contain the command, the important output, and what it proves.

Practical exercise

Apply the lesson

Starting in your home directory, go to /etc, then /var/log, then back home using only relative paths and cd -. After each cd run pwd and confirm where you are.

Before you continue

You recorded the starting state
Every command and output is understood
The change can be repeated from your notes

If something goes wrong

A command says permission denied.

Check ownership and permissions first. Do not add sudo unless the command changes a documented system location.

A command or package is not found.

Check spelling, Ubuntu version, enabled repositories, and whether the previous installation command succeeded.