Shell Basics

The built-in terminal:
  Open Applications → Utilities → Terminal

Better option — install Hyper:
  hyper.is
  Cross-platform, extensible, looks great.

The shell inside is zsh (macOS default).
It works almost identically to bash.

You'll see a prompt like:
you@mac ~ % _

Open the terminal:
  Click the Start button (or press the Win key)
  Type "terminal" and press Enter

This opens Windows Terminal (the UI).
The shell inside is PowerShell (the language).
Think of it like: Terminal is to PowerShell
as Terminal.app is to zsh.

You'll see a prompt like:
PS C:\Users\you> _

Keyboard shortcut (most distros):
  Ctrl + Alt + T

Or find "Terminal" in your app launcher.
The shell inside is bash (Linux default).

user@machine:~$ _

We recommend Hyper on all platforms:
  hyper.is

It's a modern terminal that works on
macOS, Windows, and Linux.

On Windows it runs PowerShell by default.
On macOS/Linux it runs your default shell.

/                    ← root (top of everything)
├── home/
│   └── you/         ← your home directory (~)
│       ├── Documents/
│       ├── Downloads/
│       └── projects/
├── usr/
│   ├── bin/         ← system commands live here
│   └── lib/
├── etc/             ← configuration files
└── tmp/             ← temporary files

C:\                  ← root of the C: drive
├── Users\
│   └── you\         ← your home directory (~)
│       ├── Documents\
│       ├── Downloads\
│       └── projects\
├── Program Files\   ← installed programs
├── Windows\
│   └── System32\    ← system commands
└── Temp\            ← temporary files

$ pwd                        # where am I?
/home/you

$ ls                         # what's here?
Documents  Downloads  projects

$ cd Documents               # go into Documents
$ pwd
/home/you/Documents

$ cd ..                      # go back up
$ pwd
/home/you

$ cd                         # go home (no argument = home)

PS> pwd                       # where am I?
C:\Users\you

PS> ls                        # what's here?
Documents  Downloads  projects

PS> cd Documents              # go into Documents
PS> pwd
C:\Users\you\Documents

PS> cd ..                     # go back up
PS> pwd
C:\Users\you

PS> cd ~                      # go home

$ mkdir projects/myapp       # create a directory
$ mkdir -p a/b/c             # create nested dirs

$ touch notes.txt            # create empty file

$ rmdir empty_folder         # remove empty dir
$ rm notes.txt               # remove a file
$ rm -r projects/myapp      # remove dir + contents

PS> mkdir projects/myapp
PS> New-Item a/b/c -ItemType Directory -Force

PS> New-Item notes.txt -ItemType File

PS> Remove-Item empty_folder
PS> Remove-Item notes.txt      # or: rm, del
PS> Remove-Item projects/myapp -Recurse

$ cp file.txt backup.txt        # copy a file
$ cp -r mydir/ mydir_backup/   # copy a directory

$ mv old.txt new.txt            # rename
$ mv file.txt Documents/        # move

PS> Copy-Item file.txt backup.txt
PS> Copy-Item mydir/ mydir_backup/ -Recurse

PS> Move-Item old.txt new.txt     # or: mv
PS> Move-Item file.txt Documents/

$ ls -l
drwxr-xr-x  3 you you 4096 Mar 5 10:22 Documents
-rw-r--r--  1 you you  847 Mar 5 09:11 notes.txt

$ ls -la         # include hidden files
$ ls -lh         # human-readable sizes

PS> Get-ChildItem
Mode         LastWriteTime     Length Name
d----  3/5/2026  10:22 AM            Documents
-a---  3/5/2026   9:11 AM       847  notes.txt

PS> Get-ChildItem -Force     # include hidden
PS> Get-ChildItem | Format-Table Name,Length -Auto

$ cat file.txt               # print entire file
$ head file.txt              # first 10 lines
$ head -n 3 file.txt        # first 3 lines
$ tail file.txt              # last 10 lines
$ tail -f log.txt           # follow a file (watch it grow)
$ less file.txt              # scroll through (q to quit)

PS> Get-Content file.txt      # or: cat file.txt
PS> Get-Content file.txt -Head 10
PS> Get-Content file.txt -Head 3
PS> Get-Content file.txt -Tail 10
PS> Get-Content log.txt -Wait  # follow
PS> Get-Content file.txt | Out-Host -Paging

$ grep "hello" file.txt
$ grep -i "hello" file.txt   # case-insensitive
$ grep -r "TODO" src/       # recursive
$ grep -n "error" log.txt   # line numbers

$ find . -name "*.txt"      # find by name
$ find . -type d            # dirs only
$ find /tmp -size +100M    # large files

PS> Select-String "hello" file.txt
PS> Select-String "hello" file.txt -CaseSensitive:$false
PS> Get-ChildItem src/ -Recurse | Select-String "TODO"
PS> Select-String "error" log.txt # shows line numbers by default

PS> Get-ChildItem -Recurse -Filter "*.txt"
PS> Get-ChildItem -Recurse -Directory
PS> Get-ChildItem /tmp -Recurse | Where-Object {$_.Length -gt 100MB}

$ wc file.txt                # lines, words, chars
  12   84  527 file.txt

$ wc -l file.txt             # line count only

$ sort names.txt             # alphabetical
$ sort -n numbers.txt       # numeric
$ sort -r names.txt         # reverse

$ uniq sorted.txt            # deduplicate
$ sort names.txt | uniq      # sort then deduplicate

PS> Get-Content file.txt | Measure-Object -Line -Word -Character
Lines: 12  Words: 84  Characters: 527

PS> (Get-Content file.txt).Count   # line count

PS> Get-Content names.txt | Sort-Object
PS> Get-Content nums.txt | Sort-Object {[int]$_}
PS> Get-Content names.txt | Sort-Object -Descending

PS> Get-Content sorted.txt | Get-Unique
PS> Get-Content names.txt | Sort-Object | Get-Unique

$ cut -d',' -f1 data.csv    # first CSV column

$ tr 'a-z' 'A-Z' < file.txt # uppercase
$ tr -d ' ' < file.txt      # delete spaces

$ sed 's/old/new/g' file.txt       # replace (print)
$ sed -i 's/old/new/g' file.txt   # replace (in place)

PS> Import-Csv data.csv | Select-Object -First 1
# or for raw split:
PS> (Get-Content data.csv) -split ',' | Select-Object -Index 0

PS> (Get-Content file.txt).ToUpper()
PS> (Get-Content file.txt) -replace ' ',''

PS> (Get-Content file.txt) -replace 'old','new'
PS> (Get-Content file.txt) -replace 'old','new' | Set-Content file.txt

$ date                  # date and time
$ whoami                # your username
$ hostname              # machine name
$ uname -a             # OS info
$ df -h                # disk space
$ du -sh *             # size of each item
$ ps aux                # running processes
$ top                   # live monitor (q quits)

PS> Get-Date
PS> $env:USERNAME         # or: whoami
PS> $env:COMPUTERNAME     # or: hostname
PS> Get-ComputerInfo | Select-Object OsName,OsVersion
PS> Get-PSDrive -PSProvider FileSystem
PS> Get-ChildItem | ForEach-Object { "{0,10} {1}" -f ($_.Length/1MB).ToString("0.0MB"), $_.Name }
PS> Get-Process            # or: ps
PS> # no built-in top; use Task Manager or:
PS> while($true){Get-Process | Sort-Object CPU -Desc | Select-Object -First 10; Start-Sleep 2; Clear-Host}

$ man ls                # manual page (q quits)
$ ls --help            # quick help (Linux)
$ which python          # where is this command?
$ type cd               # builtin or program?

PS> Get-Help Get-ChildItem         # help page
PS> Get-Help Get-ChildItem -Examples  # just examples
PS> Get-Command python              # where is it?
PS> Get-Command cd | Select-Object CommandType

$ echo "hello" > file.txt       # write (overwrites!)
$ echo "world" >> file.txt      # append
$ cat file.txt
hello
world

$ ls /nope 2> errors.txt        # errors only
$ command &> all.txt             # both stdout+stderr

PS> "hello" | Out-File file.txt         # write
PS> "world" | Out-File file.txt -Append # append
PS> Get-Content file.txt
hello
world

PS> Get-Item /nope 2> errors.txt        # same syntax!
PS> command *> all.txt                   # all streams

$ wc -l < file.txt            # feed file to stdin
2

$ sort < unsorted.txt > sorted.txt

# PowerShell doesn't use < for input.
# Instead, pipe file content in:
PS> (Get-Content file.txt).Count  # line count
2

PS> Get-Content unsorted.txt | Sort-Object | Out-File sorted.txt

# How many users are logged in?
$ who | wc -l
5

# How many files here?
$ ls | wc -l
12

# 5 largest files
$ du -sh * | sort -rh | head -5

# Word frequency in a file
$ tr ' ' '\n' < book.txt | sort | uniq -c | sort -rn | head -10

# Error timestamps from logs
$ grep "ERROR" app.log | cut -d' ' -f1,2 | sort | uniq -c

# How many processes running?
PS> Get-Process | Measure-Object
Count: 142

# How many files here?
PS> (Get-ChildItem).Count
12

# 5 largest files
PS> Get-ChildItem | Sort-Object Length -Desc | Select-Object -First 5 Name,Length

# Word frequency in a file
PS> (Get-Content book.txt) -split '\s+' | Group-Object | Sort-Object Count -Desc | Select-Object -First 10

# Error timestamps from logs
PS> Select-String "ERROR" app.log | ForEach-Object { $_.Line.Split(' ')[0..1] -join ' ' } | Group-Object | Sort-Object Count -Desc

# Get PIDs of node processes
$ ps aux | grep node | awk '{print $2}'
1234
5678
# Fragile: depends on column position

# Get PIDs of node processes
PS> Get-Process node | Select-Object Id
1234
5678
# Robust: .Id is a typed property

$ NAME="world"               # no spaces around =
$ echo "hello $NAME"

$ echo $HOME                 # env variable
$ echo $PATH
$ export API_KEY="secret"    # set for child processes
$ env                        # list all env vars

# Command substitution
$ TODAY=$(date +%Y-%m-%d)
$ echo "Today is $TODAY"

PS> $NAME = "world"            # spaces OK
PS> "hello $NAME"

PS> $HOME                      # built-in variable
PS> $env:PATH                  # env: prefix
PS> $env:API_KEY = "secret"
PS> Get-ChildItem env:         # list all env vars

# Command substitution
PS> $TODAY = Get-Date -Format "yyyy-MM-dd"
PS> "Today is $TODAY"

$ ps aux                     # all processes
$ ps aux | grep node         # find by name
$ kill 1234                  # graceful stop
$ kill -9 1234              # force kill
$ command &                 # run in background
$ jobs                       # list bg jobs
$ fg                         # bring to foreground

PS> Get-Process
PS> Get-Process | Where-Object {$_.Name -like "node*"}
PS> Stop-Process -Id 1234
PS> Stop-Process -Id 1234 -Force
PS> Start-Job { command }     # background
PS> Get-Job                   # list bg jobs
PS> Receive-Job -Id 1        # get output

$ cd Doc[Tab]
$ cd Documents/           # completed!

$ git sta[Tab]
$ git status              # completed!

$ ls *.tx[Tab]
file.txt  notes.txt  readme.txt  # multiple matches shown

PS> cd Doc[Tab]
PS> cd .\Documents\        # completed!

PS> Get-Chi[Tab]
PS> Get-ChildItem          # completed!

# Keep pressing Tab to cycle through matches
PS> Get-Com[Tab][Tab][Tab]

Up           # previous command
Down         # next command
Ctrl+R       # search history (type to filter)
$ history    # show full history list
$ !grep      # re-run last command starting with "grep"
$ !!         # re-run the very last command

Up           # previous command
Down         # next command
Ctrl+R       # search history (same!)
PS> Get-History          # show full history
PS> Invoke-History 5     # re-run command #5
F8           # search history by prefix

Cmd+C     # copy selected text
Cmd+V     # paste

# In iTerm2 / Hyper:
# Select text to auto-copy
# Middle-click or Cmd+V to paste

Ctrl+Shift+C   # copy (not Ctrl+C!)
Ctrl+Shift+V   # paste

# Or: select text, right-click to copy
# Right-click again to paste

# Ctrl+C in a terminal means "cancel"
# so copy needs the Shift modifier

#!/bin/bash
# first argument passed to the script
NAME=$1

if [ -z "$NAME" ]; then
    echo "Usage: ./greet.sh <name>"
    exit 1
fi

echo "Hello, $NAME!"
echo "Today is $(date +%A)."
echo "You are in $(pwd)."

# first argument passed to the script
param([string]$Name)

if (-not $Name) {
    Write-Host "Usage: .\greet.ps1 <name>"
    exit 1
}

Write-Host "Hello, $Name!"
Write-Host "Today is $((Get-Date).DayOfWeek)."
Write-Host "You are in $(Get-Location)."

$ chmod +x greet.sh      # make executable (once)
$ ./greet.sh Alice
Hello, Alice!
Today is Thursday.
You are in /home/you.

# no chmod needed on Windows
PS> .\greet.ps1 -Name Alice
Hello, Alice!
Today is Thursday.
You are in C:\Users\you.

GREETING="Hello"
NAME="World"
echo "$GREETING, $NAME!"

# Command substitution
TODAY=$(date +%Y-%m-%d)
FILES=$(ls | wc -l)
echo "Date: $TODAY, Files: $FILES"

# WRONG — no spaces around =
# NAME = "bad"  <-- error!

$greeting = "Hello"
$name = "World"
"$greeting, $name!"

# Command substitution
$today = Get-Date -Format "yyyy-MM-dd"
$files = (Get-ChildItem).Count
"Date: $today, Files: $files"

# Spaces around = are fine
# $name = "good"  <-- works!

FILE=$1

if [ -f "$FILE" ]; then
    echo "$FILE is a file."
    echo "$(wc -l < "$FILE") lines"
elif [ -d "$FILE" ]; then
    echo "$FILE is a directory."
else
    echo "$FILE does not exist."
fi

$file = $args[0]

if (Test-Path $file -PathType Leaf) {
    "$file is a file."
    "$((Get-Content $file).Count) lines"
} elseif (Test-Path $file -PathType Container) {
    "$file is a directory."
} else {
    "$file does not exist."
}

# Loop over a list
for fruit in apple banana cherry; do
    echo "I like $fruit"
done

# Loop over files
for f in *.txt; do
    echo "$f: $(wc -l < "$f") lines"
done

# Loop with numbers
for i in $(seq 1 5); do
    echo "Count: $i"
done

# While loop
COUNT=0
while [ $COUNT -lt 5 ]; do
    echo "Tick: $COUNT"
    COUNT=$((COUNT + 1))
done

# Loop over a list
foreach ($fruit in "apple","banana","cherry") {
    "I like $fruit"
}

# Loop over files
foreach ($f in Get-ChildItem *.txt) {
    "$($f.Name): $((Get-Content $f).Count) lines"
}

# Loop with numbers
1..5 | ForEach-Object {
    "Count: $_"
}

# While loop
$count = 0
while ($count -lt 5) {
    "Tick: $count"
    $count++
}

#!/bin/bash

SOURCE=$1
if [ -z "$SOURCE" ] || [ ! -d "$SOURCE" ]; then
    echo "Usage: ./backup.sh <dir>"
    exit 1
fi

TS=$(date +%Y%m%d_%H%M%S)
BACKUP="${SOURCE}_backup_${TS}.tar.gz"

tar czf "$BACKUP" "$SOURCE"
SIZE=$(du -h "$BACKUP" | cut -f1)
echo "Backed up to $BACKUP ($SIZE)"

param([Parameter(Mandatory)]
      [string]$Source)

if (-not (Test-Path $Source -PathType Container)) {
    Write-Error "Not found: $Source"
    exit 1
}

$ts = Get-Date -Format "yyyyMMdd_HHmmss"
$backup = "${Source}_backup_${ts}.zip"

Compress-Archive -Path $Source -DestinationPath $backup
$mb = [math]::Round((Get-Item $backup).Length/1MB, 1)
"Backed up to $backup ($mb MB)"