Day 2 — Terminal Navigation#

Goal: Move around the Linux filesystem with confidence using pwd, ls, cd, and tree — so you never feel lost in the terminal.

Where Am I? — pwd#

The first command to learn. Run it whenever you are lost:

pwd
# /home/alice/projects/tds

pwd = Print Working Directory. It tells you the absolute path of where your terminal is right now.

Every command you run operates relative to this location. If you run ls, it lists what’s in this directory. If you run python3 script.py, it looks for script.py here.

What Is Here? — ls#

ls shows you what’s in a directory. You will use this hundreds of times a day.

Basic usage#

ls                    # list files in current directory
ls /home/alice/       # list files in a specific directory
ls ~/projects/        # list files in home/projects

Essential flags#

ls -l                 # long format: permissions, size, date
ls -a                 # show hidden files (starting with .)
ls -la                # both — the most useful combo
ls -lh                # human-readable sizes (KB, MB, GB)
ls -lt                # sort by modification time (newest first)
ls -lS                # sort by file size (largest first)
ls -R                 # recursive — list subdirectories too

Reading ls -la output#

ls -la
# drwxr-xr-x  4 alice alice 4096 Jan 15 10:23 .
# drwxr-xr-x 12 alice alice 4096 Jan 15 09:00 ..
# -rw-r--r--  1 alice alice  234 Jan 15 10:23 README.md
# -rwxr-xr-x  1 alice alice  891 Jan 14 18:45 run.sh
# drwxr-xr-x  2 alice alice 4096 Jan 14 15:30 data

Breaking down a line:

-rw-r--r--  1  alice  alice  234  Jan 15 10:23  README.md
│             │      │       │    │              │
│             owner  group   size  date          filename
│
└─ permissions:
   - = regular file (d = directory, l = symlink)
   rw- = owner can read+write
   r-- = group can read
   r-- = others can read

Glob patterns with ls#

ls *.py               # all Python files
ls data_*.csv         # files starting with "data_" ending in ".csv"
ls -la *.md           # long listing of all Markdown files

🧠 Knowledge Check#

Q1: What does the command ls -la do?

  • A) Lists only hidden files
  • B) Lists all files (including hidden ones) in a long format showing permissions and size
  • C) Lists files sorted by size
  • D) Lists directories only
Answer

B — -l stands for long format, and -a stands for all (including hidden .dotfiles).

Move Around — cd#

cd = Change Directory. This is how you navigate.

# Absolute path
cd /home/alice/projects

# Relative path
cd projects           # goes into projects/ from current dir
cd data/raw/          # goes into nested directories

# Go UP
cd ..                 # parent directory (one level up)
cd ../..              # grandparent (two levels up)

# Go HOME
cd ~                  # home directory
cd                    # same as cd ~ (no argument)
cd $HOME              # same thing using env variable

# Go BACK to previous location
cd -                  # toggle between current and previous

cd - — The back button#

This is incredibly useful:

cd ~/projects/tds/week1/data/
# do some work...
cd /etc/
# check something...
cd -
# /home/alice/projects/tds/week1/data/  ← back where you were!

See the Tree — tree#

tree shows a visual representation of your directory structure. It’s not always installed by default:

# Install it:
sudo apt install tree -y

Usage#

tree                  # full tree from current directory
tree -L 2             # limit depth to 2 levels
tree -a               # include hidden files
tree -d               # directories only (no files)
tree -sh              # show file sizes in human-readable format
tree ~/projects/      # tree of a specific path

Example output#

tree -L 2
# .
# ├── day-1
# │   └── README.md
# ├── day-2
# │   ├── data
# │   ├── outputs
# │   └── scripts
# └── README.md

Save tree output to a file#

tree -L 2 > structure.txt
cat structure.txt

🧠 Knowledge Check#

Q1: Why is it recommended to use the -L flag with tree?

  • A) To list files alphabetically
  • B) To show long file properties
  • C) To limit the depth of the directory tree displayed, preventing the terminal from being flooded with thousands of lines
  • D) To display only symlinks
Answer

C — The -L flag (Level) restricts how deep tree goes, which is crucial in large directories.

Creating Directories — mkdir#

mkdir mydir                           # create a directory
mkdir -p a/b/c/d                      # create nested directories
mkdir -p project/{src,tests,docs}     # create multiple at once

The -p flag is essential:

  • Creates parent directories as needed
  • Doesn’t error if the directory already exists

Brace expansion for multiple directories#

mkdir -p ~/tds-bootcamp/{day-1,day-2,day-3,day-4,day-5}
# Creates all five day directories in one command

mkdir -p ~/tds-bootcamp/day-2/{data,outputs,scripts}
# Creates three subdirectories inside day-2

Putting It All Together#

Here’s a typical navigation workflow:

# 1. Start at home
cd ~
pwd                    # /home/alice

# 2. Create a workspace
mkdir -p ~/tds/bootcamp/day-2
cd ~/tds/bootcamp/day-2
pwd                    # /home/alice/tds/bootcamp/day-2

# 3. See what's here
ls -la                 # nothing yet (empty directory)

# 4. Create some structure
mkdir -p data scripts outputs
ls                     # data  outputs  scripts

# 5. Verify with tree
tree ..                # shows day-2 structure from parent

Q&A#

Q: What happens if I type cd with no arguments?

A: It takes you to your home directory (~). Same as cd ~ or cd $HOME.

Q: What is the difference between ls and ls -a?

A: ls hides files starting with . (dotfiles). ls -a shows everything, including hidden files like .bashrc, .gitconfig, .ssh/. These hidden files are typically configuration files.

Q: Can I use tree on large directories?

A: Yes, but always use -L to limit depth. Running tree / without limits will flood your terminal with thousands of lines. tree -L 2 is a safe starting point.

Q: What does . and .. mean in ls -la output?

A:

  • . = the current directory itself
  • .. = the parent directory

Every directory contains these two entries. They are how cd . (stay here) and cd .. (go up) work.

Exercises#

Exercise 1: Navigate and report

cd /usr/bin
pwd
ls | wc -l       # How many programs are installed?
cd ~
pwd
What did you find?
  • pwd after cd /usr/bin → /usr/bin
  • ls | wc -l → likely 1000+ programs (varies by system)
  • pwd after cd ~ → /home/yourname

This shows /usr/bin contains hundreds/thousands of programs that came with your system.

Exercise 2: Create and explore

mkdir -p ~/nav-practice/{alpha,beta,gamma}/{data,logs}
tree ~/nav-practice/ -L 2

Now navigate using only relative paths:

cd ~/nav-practice/alpha/data
pwd                              # should be /home/you/nav-practice/alpha/data
cd ../../beta/logs
pwd                              # should be /home/you/nav-practice/beta/logs
cd ../../gamma
pwd                              # should be /home/you/nav-practice/gamma
Check your answers
  1. After cd ~/nav-practice/alpha/data → /home/you/nav-practice/alpha/data ✓
  2. After cd ../../beta/logs → from alpha/data, up 2 = nav-practice/, then into beta/logs ✓
  3. After cd ../../gamma → from beta/logs, up 2 = nav-practice/, then into gamma ✓

Clean up:

rm -r ~/nav-practice

Exercise 3: MCQ

Q1: What does cd - do?

  • A) Goes to the root directory
  • B) Goes to the home directory
  • C) Goes to the previous directory you were in
  • D) Goes up one level
Answer

C — cd - toggles between your current directory and the last directory you were in. Like a “back” button.

Q2: You run ls -la and see a line starting with d. What does the d mean?

  • A) The file has been deleted
  • B) It is a directory
  • C) It is a device file
  • D) It is a dotfile
Answer

B — d at the start means it’s a directory. - means regular file, l means symlink.

Q3: What command creates /home/alice/a/b/c/ when only /home/alice/ exists?

  • A) mkdir /home/alice/a/b/c/
  • B) mkdir -r /home/alice/a/b/c/
  • C) mkdir -p /home/alice/a/b/c/
  • D) touch /home/alice/a/b/c/
Answer

C — The -p flag creates parent directories as needed. Without -p, mkdir would fail because a/ and b/ don’t exist yet.