28  Lecture 5 (Pre) — Linux Basics

29 Linux Basics — 75‑Minute Lecture (Colab Edition, using vim)

Audience: Absolute beginners to Linux

Format: using ! (line) or %%bash (cell) magics. Editing demo uses vim

29.1 Learning Outcomes

By the end, students will be able to:

  • Explain what Linux, the shell, and the filesystem are
  • Navigate directories and inspect files
  • Create, copy, move, and delete files/directories safely
  • Use wildcards, pipes, and redirection to combine commands
  • Understand permissions and make a script executable
  • Edit a text file in vim (open, insert, save, quit)
  • Run shell scripts in Colab and install packages (apt/pip)

29.2 Colab Setup (2–3 min)

Colab uses a Linux VM with a working directory at /content. To run shell commands in Colab:

  • One‑liner: prefix with !
  • Multi‑line: start a cell with %%bash
# Verify we’re on Linux
!uname -a
!lsb_release -a || cat /etc/os-release
# Where are we?
!pwd
!ls -lah

Persistence: Colab VMs reset. To keep files between sessions, mount Google Drive:

from google.colab import drive
drive.mount('/content/drive')
!ls -lah /content/drive/MyDrive

29.3 Agenda (timeboxed)

  • (0–10) What is Linux? Shell vs kernel. Filesystem anatomy.
  • (10–25) Navigation + basic file ops
  • (25–35) Permissions & ownership (Colab nuances)
  • (35–50) Redirection, pipes, text tools (grep, sort, wc, cut)
  • (50–60) vim crash course (editing in a real terminal)
  • (60–70) Shell scripts, variables, PATH
  • (70–75) Packages (apt/pip) + help/man + wrap‑up

29.4 1) What is Linux? (0–10 min)

  • Kernel: talks to hardware; Userland: tools (bash, ls, vim, etc.)
  • Shell: the program that reads your commands (default in Colab: bash).
  • Filesystem: a tree with root / (not “C:”), home ~, current . and parent ...
  • Common paths: /bin, /usr/bin (programs), /home/… (homes), /etc (config), /var (logs), /tmp (temp). In Colab, workspace is /content and you often store persistent data under /content/drive/MyDrive/....

Mini‑lab:

!echo $SHELL
!whoami
!pwd
!ls -lah /

29.6 3) Permissions & Ownership (25–35 min)

ls -l output: -rwxr-xr-- 1 owner group size date name

  • First char - file / d directory
  • Triplets rwx for user/group/others (read/write/execute)
  • Change mode: chmod u+x script.sh (add execute for user)

Colab note: you usually run as root, so ownership quirks differ from multi‑user systems. Still practice chmod and safe deletions.

Mini‑lab:

%%bash
cd /content/play
cat > hello.sh <<'EOF'
#!/usr/bin/env bash
echo "Hello from a script"
EOF
ls -l hello.sh
chmod u+x hello.sh
./hello.sh

29.7 4) Redirection, Pipes, & Essential Text Tools (35–50 min)

Redirection

  • > overwrite, >> append, 2> stderr, &> stdout+stderr
  • | pipe: feed output of left command into right command

Tools

  • grep PATTERN (search); -n show line numbers, -i case‑insensitive
  • wc -l (line count), sort, uniq -c, cut -d, -f1, tr, tee

Mini‑lab:

%%bash
cd /content/play
# Make a small CSV
cat > stocks.csv <<'EOF'
ticker,price
AAPL,180
MSFT,420
AAPL,181
NVDA,120
AAPL,182
EOF
# Count rows, list unique tickers with counts
wc -l stocks.csv
cut -d, -f1 stocks.csv | tail -n +2 | sort | uniq -c | sort -nr
# Filter rows with AAPL and take last 2
grep '^AAPL,' stocks.csv | tail -n 2

29.8 5) vim Crash Course (50–60 min)

Goal: basic edits: open → insert → save → quit.

Install (if needed):

!apt-get update -qq && apt-get install -y -qq vim

Colab caution: vim is fully interactive; works best in a Terminal session (Colab’s Connect to a terminal feature or a local terminal/WSL). If you can’t open a real terminal, use the heredoc technique shown earlier to create/edit files.

vim basics

  • Launch: vim hello.txt
  • Modes: Normal (default), Insert (i), Command (:)
  • Insert text: press i, type; ESC to leave insert
  • Save & quit: :wq • Quit without saving: :q! • Save: :w
  • Navigation: arrows or h j k l; jump to line :42
  • Search: /pattern then n/N

Exercise (in a real terminal):

  1. vim notes.txt
  2. Press i, type a few lines
  3. ESC, then :wq
  4. cat notes.txt

29.9 6) Shell Scripts, Variables, PATH (60–70 min)

Variables

NAME=Alice
echo "Hi $NAME"

Script + shebang

#!/usr/bin/env bash
set -euo pipefail
NAME=${1:-World}
echo "Hello, $NAME!"

Colab demo:

%%bash
cd /content/play
cat > greet.sh <<'EOF'
#!/usr/bin/env bash
set -euo pipefail
NAME=${1:-World}
echo "Hello, $NAME!"
EOF
chmod u+x greet.sh
./greet.sh
./greet.sh Linux

PATH

  • Shows where the shell looks for executables.
!echo $PATH
!which python
  • Run from current dir with ./script.sh (current dir isn’t automatically in PATH).

29.10 7) Packages & Help (70–75 min)

System packages (apt)

!apt-get update -qq
!apt-get install -y -qq tree  # example
!tree -L 2 /content/play

Python packages (pip)

%pip install -q pandas
python -c "import pandas as pd; print(pd.__version__)"

Getting help

  • cmd --help (portable) • man cmd (manual; may be minimal in Colab)
  • apropos to search manuals; tldr if installed for concise examples

29.11 Mini‑Labs (for practice / homework)

  1. Find & count: In /usr/bin, count how many programs start with g.

    !ls -1 /usr/bin/g* 2>/dev/null | wc -l

  2. CSV pipeline: From stocks.csv, output the max price per ticker.

    %%bash
cd /content/play
awk -F, 'NR>1 {max[$1] = ($2>max[$1] ? $2 : max[$1])} END {for (k in max) print k "," max[k]}' stocks.csv | sort

  3. Permissions: Make a script that fails without execute bit; then add it and rerun.

  4. vim: Create todo.txt with three lines and save.

29.12 One‑Page Cheat Sheet

Navigation: pwd, ls -lah, cd, mkdir -p, tree (optional)

Files: touch, cp, mv, rm [-r], cat, less, head, tail, find, grep -R

Globs: *, ?, [abc], {a,b}

Pipes/Redirection: |, >, >>, 2>, &>; tee

Text tools: grep, sort, uniq -c, wc -l, cut, tr, awk

Permissions: ls -l, chmod u+x, umask

Processes: ps aux, top -bn1, kill PID

Editing (vim): i insert, ESC normal, :w save, :q quit, :wq save+quit, :q! force quit

Scripts: #!/usr/bin/env bash, chmod +x, ./script.sh

Packages: apt-get update, apt-get install -y PKG; Python: %pip install PKG

Help: cmd --help, man cmd, which cmd, type cmd