Day 1 — Unix Basics

Learning Objectives

Explain how the shell relates to the keyboard, screen, OS, and user programs
Explain when and why to use command-line interfaces instead of GUIs
Explain the difference between a file and a directory
Translate between absolute and relative paths
Use options and arguments to change command behavior
Use tab completion effectively

Setup

WSL (Windows users)Windows Subsystem for Linux
Git for WindowsAlternative for Windows users
shell-lesson-data.zipWorkshop dataset — download and unzip to your Desktop
Carpentries lessonOfficial lesson page we follow today

The Shell Prompt

Open your terminal. You should see a prompt — this means the shell is ready for input.

bash

$ |        # The prompt — hey, it's working!
$ ls       # List files in the current directory (your home directory)
$ pwd      # Print working directory — where are you?

Windows users

If you're using WSL, navigate to your Windows files with: cd /mnt/c/<your username>

Navigating Directories

cd (change directory) is the most-used command you'll learn today. Master it.

bash

$ cd /             # Go to the root of the filesystem
$ cd               # Shortcut: go back to your home directory
$ cd ~/            # Same thing — ~ always means home
$ cd Desktop/shell-lesson-data/exercise-data

Tab complete — use it constantly

Press Tab after typing the first few letters of a path. The shell completes it for you. If nothing happens, press Tab twice to see all options. Try misspelling something to see what the error looks like: cd Desktap/shell-lesson-data

Moving Up and Around

bash

$ cd ..            # Move up one directory level
$ cd exercise-data # Move into a subdirectory
$ cd -             # Go back to the previous directory

Problem — predict the outcome

What directory will this move you to? cd ../..
Come up with two ways to navigate back to the directory containing the workshop data.

Up and down arrows

Use the up/down arrow keys to scroll through your command history — you don't have to retype commands.

Listing Files and Using Flags

Flags modify how a command behaves. They start with a dash -.

bash

$ ls -l            # Long format — shows permissions, size, date
$ ls -lF           # Adds "/" after directory names
$ ls -lah          # Long format, all files (including hidden), human-readable sizes
$ clear            # Clear the terminal screen
$ man ls           # Read the manual for ls — press q to exit

Problem #1

Use the manual (man ls) to determine how to add color to the output of ls. Answer: ls -G

Pipes, Wildcards, and Viewing Files

The real power of Unix comes from combining commands. The pipe | sends the output of one command into the input of another.

bash

$ ls -F | grep \/ > directories.txt
# | pipes output into grep (a search tool)
# grep \/ searches for "/" (i.e., directories)
# > writes the output to a new file called directories.txt

Viewing File Contents

bash

$ head directories.txt      # Show first 10 lines
$ tail directories.txt      # Show last 10 lines
$ less directories.txt      # Scroll through the file (press q to exit)
$ more directories.txt      # Similar to less

Wildcards

The wildcard * matches any number of characters. Navigate to ~/Desktop/shell-lesson-data/north-pacific-gyre and try:

bash

$ wc -l NENE01736A.txt      # Count lines in one file
$ wc -l *.txt               # Count lines in ALL .txt files

Absolute vs. Relative Paths

bash

$ cd ~/Desktop/shell-lesson-data
$ head -5 exercise-data/directories.txt   # relative path — works
$ head -5 directories.txt                 # why doesn't this work?
$ head -5 ~/Desktop/shell-lesson-data/exercise-data/directories.txt  # absolute path
$ rm directories.txt                      # remove the file when done

Ask AI to Explain a Pipeline AI

Pipelines can be hard to read at first. Use AI to break them down. Try this prompt:

Try this prompt in Claude or ChatGPT

I'm learning Unix shell commands. Can you explain what this pipeline does, step by step? ls -F | grep \/ > directories.txt Please explain each part: what ls -F does, what the pipe | does, what grep \/ does, and what > directories.txt does.

Then try modifying the command — ask AI what would happen if you changed \/ to something else, or used >> instead of >.