Lecture 2 - Hello Shell!

Intro

And the survey says...

Some FAQs

Common questions

• Exam format and content
• How I learned your names
• Where are recordings / lecture notes
• Partial credit / extra credit
• How bad til exams get a curve?

Some more points to note

• Gradescope vs GitHub Classroom
• Lecture notes for A vs B

I promise to revisit these Monday:

• Prework
• Homework and exam schedule

Motivation

What is the terminal?

What is the terminal?

... the kitchem metaphor

Shell, Terminal, Console, Command line... and what's Bash?

• The command line is the interface where you type commands to interact with your computer.
• The command prompt is the character(s) before your cursor that signals you can type and can be configured with other reminders.
• The terminal or console is the program that opens a window and lets you interact with the shell.
• The shell is the command line interpreter that processes your commands. (You might also encounter "a command line" in text-based games)

Terminals are more like applications and shells are more like languages.

Shell, Terminal, Console, Command line... and what's Bash?

Terminals come in proper nouns:

• Terminal (macOS)
• iTerm2 (macOS)
• GNOME Terminal (Linux)
• Konsole (Linux)
• Command Prompt (Windows)
• PowerShell (Windows)
• Git Bash (Windows)

Shells also come in proper nouns:

• Bash (Bourne Again SHell) - most common on Linux and macOS
• Zsh (Z Shell) - default on modern macOS
• Fish (Friendly Interactive SHell) - user-friendly alternative
• Tcsh (TENEX C Shell) - popular on some Unix systems
• PowerShell - advanced shell for Windows

Shell, Terminal, Console, Command line... and what's Bash?

BUT they are often used interchangeably in speech:

• "Open your terminal"
• "Type this command in the shell"
• "Run this in the command line"
• "Execute this in your console"

What is this all good for?

Lightning fast navigation and action

# Quick file operations
ls *.rs                    # Find all Rust files
grep "TODO" src/*.rs       # Search for TODO comments across files
wc -l data/*.csv          # Count lines in all CSV files

• How would you to this "manually"?

It's how we're going to build and manage our rust projects

# Start your day
git pull                          # Get latest team changes
cargo test                        # Make sure everything still works
# ... code some features ...
cargo run                         # Test your new feature
git add src/main.rs               # Stage your changes
git commit -m "Add awesome feature"  # Save your work
git push                          # Share with the team

For when your UI just won't cut it

• Confused by "invisible files" and folders?

ls -la

For when your UI just won't cut it

• Need to find a file where you wrote something a while ago

grep -r "that thing I wrote 6 months ago"

• Modify lots of files at once

# Rename 500 photos at once
for file in *.jpg; do mv "$file" "vacation_$file"; done

# Delete all files older than 30 days
find . -type f -mtime +30 -delete

• "Why is my computer fan running like it's about to take off?"

df -h              # See disk space usage immediately
ps aux | grep app  # Find that app that's hogging memory
top                # Live system monitor

In other words, the command line provides:

• Speed: Much faster for repetitive tasks
• Precision: Exact control over file operations
• Automation: Commands can be scripted and repeated
• Remote work: Essential for server management
• Development workflow: Many programming tools use command-line interfaces

Learning objectives for today (TC 12:30)

By the end of this lecture, you should be able to:

• Navigate your file system on the command line
• Create, copy, move, and delete files and directories at the command line
• Interpret file permissions
• Use pipes and redirection for basic text processing

We will also discuss, but you are not responsible for:

• Customizing your shell profile with aliases and functions
• Writing simple shell scripts

We'll have one of these slides every lecture and it's a great way to check in on what material you're responsible for for exams!

The file system and navigation

Everything starts at the root

Root Directory (/):

In Linux, the slash character represents the root of the entire file system.

(On a Windows machine you might see "C:" but on Linux and MacOS it is just "/".)

(We'll talk more about Windows in a minute)

Key Directories You'll Use:

/                          # Root of entire system
├── home/                  # User home directories
│   └── username/          # Your personal space
├── usr/                   # User programs and libraries
│   ├── bin/              # User programs (like cargo, rustc)
│   └── local/            # Locally installed software
└── tmp/                  # Temporary files

Navigation Shortcuts:

• ~ = Your home directory
• . = Current directory
• .. = Parent directory
• / = Root directory

Let's take a look / basic navigation demo

Demo time! First let's look at the command prompt...

Maybe half of your interactions with the shell will look like:

pwd                   # Print working directory
ls                    # List files in current directory
ls -a                 # List files including hidden files
ls -al                # List files with details and hidden files
cd directory_name     # Change to directory
cd ..                 # Go up one directory
cd ~                  # Go to home directory

Tips:

• Use Tab for auto-completion (great for paths!)
• Use Up Arrow to access command history
• Try control-c to abort something running or clear a line
• You can't click into a line to edit it, use left/right arrows (or vim, or copy-paste)

What's going on here?

The command line takes commands and arguments.

ls -la ~

The grammer is like a command in English: VERB (NOUN) ("eat", "drink water", "open door") ls is the command, -la and ~ are arguments.

Flags / Options

Special arguemnts called "options" or "flags" usually start with a dash - and can be separate or combined. These are equivalent:

ls -la
ls -al
ls -a -l
ls -l -a

BUT they typically need to come before other arguemnts:

ls -l -a ~   # works!
ls -l ~ -a   # does not work

Let's pause for the elephant in the room

• macOS is built on Unix
• Windows is entirely different
  • dir instead of ls
  • copy and move instead of cp and mv
• We strongly recommend Windows users install a terminal with bash (we'll do it today!) so we can speak the same language.

One thing is unavoidable: different paths

• / vs C:\Users\ (vote for which is a back slash!)
• This incompatibility has caused more suffering than metric vs imperial units.

Essential Commands for Daily Use (TC 12:35)

Quiz time!

What do these stand for and what do they do:

• pwd
• cd
• ls

And

• How can you "get home quickly"?

These slides make a great starting point for Anki questions!

Reverse, reverse!

• How can you see what directory you're in?
• How can you look around to see what's in the folder?
• How can you go into one of those folders?
• How can you back out?
• How can you see hidden files?

The rest of the 80% of bash commands you will mostly ever use

Demo time!

mkdir project_name        # Create directory
mkdir -p path/to/dir      # Create nested directories
touch notes.txt        # Create empty file
echo "Hello World" > notes.txt  # Overwrite file contents
echo "It is me" >> notes.text   # Append to file content

cat filename.txt          # Display entire file
head filename.txt         # Show first 10 lines
tail filename.txt         # Show last 10 lines
less filename.txt         # View file page by page (press q to quit)
nano filename.txt          # Edit a file

cp file.txt backup.txt    # Copy file
mv old_name new_name      # Rename/move file
rm filename               # Delete file
rm -r directory_name      # Delete directory and contents
rm -rf directory_name     # Delete dir and contents without confirmation

Understanding ls -la Output

-rw-r--r-- 1 user group 1024 Jan 15 10:30 filename.txt
drwxr-xr-x 2 user group 4096 Jan 15 10:25 dirname

(Don't worry about "groups"!)

We will see these kinds of permissions again in Rust programming!

Common Permission Patterns

• 644 or rw-r--r--: Files you can edit, others can read
• 755 or rwxr-xr-x: Programs you can run, others can read/run
• 600 or rw-------: Private files only you can access

(Any guesses about the numeric codes?)

Don't have permission? Don't tell anyone I told you this but...

Don't have permission? Don't tell anyone I told you this but...

• What do you think sudo stands for?

One list thing... Combining Commands with Pipes

ls | grep ".txt"          # List only .txt files
cat file.txt | head -5    # Show first 5 lines of file
ls -l | wc -l            # Count number of files in directory

Combining Commands with Pipes

More Examples:

# Find large files
ls -la | sort -k5 -nr | head -10

# Count total lines in all text files
cat *.txt | wc -l

So tell me, what's the difference...

ls -la | wc -l
ls -la > results.txt

FYI (TC 12:45 or skip)

For your awareness - Your Shell Profile

Understanding Shell Configuration Files:

Your shell reads a configuration file when it starts up. This is where you can add aliases, modify your PATH, and customize your environment.

Common Configuration Files:

• macOS (zsh): ~/.zshrc
• macOS (bash): ~/.bash_profile or ~/.bashrc
• Linux (bash): ~/.bashrc
• Windows Git Bash: ~/.bash_profile

Finding Your Configuration File:

It's in your Home directory.

# Check which shell you're using (MacOS/Linus)
echo $SHELL

# macOS with zsh
echo $HOME/.zshrc

# macOS/Linux with bash
echo $HOME/.bash_profile
echo $HOME/.bashrc

Adding aliases to you shell profile

# Edit your shell configuration file (choose the right one for your system)
nano ~/.zshrc        # macOS zsh
nano ~/.bash_profile # macOS bash or Git Bash
nano ~/.bashrc       # Linux bash

# Add these helpful aliases:
alias ll='ls -la'
alias ..='cd ..'
alias ...='cd ../..'
alias projects='cd ~/development'
alias rust-projects='cd ~/development/rust_projects'
alias grep='grep --color=auto'
alias tree='tree -C'

# Custom functions
# This will make a directory specified as the argument and change into it
mkcd() {
    mkdir -p "$1" && cd "$1"
}

Modifying your PATH

You may need to do this occasionally to make tools you install available on the command line.

# Add to your shell configuration file
export PATH="$HOME/bin:$PATH"
export PATH="$HOME/.cargo/bin:$PATH"    # For Rust tools (we'll add this later)

# For development tools
export PATH="/usr/local/bin:$PATH"

Applying Changes:

# Method 1: Reload your shell configuration
source ~/.zshrc        # For zsh
source ~/.bash_profile # For bash

# Method 2: Start a new terminal session
# Method 3: Run the command directly
exec $SHELL

Shell scripts

Shell script files typically use the extension *.sh, e.g. script.sh.

Shell script files start with a shebang line, #!/bin/bash.

#!/bin/bash

echo "Hello world!"

To execute shell script you can use the command:

source script.sh

Before it gets noisy in here... (TC 12:50)

• What does drwxr-xr-x mean?
• How can I quickly write "I'm awesome" to my affirmations.txt file?
• How can I delete my file_of_secrets.txt before the cops get here?
• How can I rename my file_of_secrets.txt so it "disappears"?
• How can I find it again?

In-Class Activity: Shell Challenge

In groups of 2-3, go to https://github.com/lauren897/ds210-fa25-b and complete the challenge.

Remember to submit on gradescope (once per group)! (There's a grace period til 1:30)

Coming up -

• Monday: git and GitHub
• Releasing HW1 (exact dates TBD but we'll give at least a full week)
• We start Rust on Wednesday!
• Wednesday also starts pre-work, we'll explain more on Monday
• I'll post a coffee slot sign-up sheet tonight
• I'll have lecture notes / a site set up by Monday