Bash — Complete Beginner Tutorial

# pwd — Print Working Directory (where am I right now?)
pwd

# ls — List files and folders here
ls

# ls -l — Long format: shows permissions, size, date
ls -l

# ls -la — Also show hidden files (files starting with a dot)
ls -la

# cd — Change Directory (move into a folder)
cd Documents

# cd .. — Go UP one level (to the parent folder)
cd ..

# cd ~ — Go to your home directory (always works!)
cd ~

# cd /var/log — Go to an absolute path
cd /var/log

# mkdir — Make a new directory (folder)
mkdir my_project
mkdir -p projects/2025/april   # -p creates parent folders too

# touch — Create an empty file
touch hello.sh
touch notes.txt config.json

# cp — Copy a file
cp hello.sh hello_backup.sh

# cp -r — Copy a whole folder (recursively)
cp -r my_project my_project_backup

# mv — Move or rename a file
mv notes.txt Documents/notes.txt    # move to folder
mv hello.sh greet.sh                # rename

# rm — Remove (delete) a file — NO UNDO!
rm old_file.txt

# rm -r — Remove a whole folder and everything in it
rm -r my_project_backup

# Echo the result
echo "Files in current directory:"
ls

# cat — Print the whole file to the terminal
cat notes.txt

# head — Show first 10 lines
head server.log

# head -n 5 — Show first 5 lines
head -n 5 server.log

# tail — Show last 10 lines
tail server.log

# tail -f — Follow the file live (great for logs!)
# tail -f /var/log/syslog

# grep — Search for a pattern in a file
grep "error" server.log

# grep -i — Case-insensitive search
grep -i "ERROR" server.log

# grep -n — Show line numbers
grep -n "Alice" users.txt

# wc -l — Count lines in a file
wc -l server.log

#!/bin/bash

# Assign variables — NO spaces around =
name="Alice"
age=25
city="Cape Town"
pi=3.14

# Read variables with $
echo $name
echo $age

# Better: use double quotes (handles spaces in values)
echo "Hello, $name!"
echo "You are $age years old."

# Curly braces: useful when variable name is next to text
version=3
echo "Python${version} is great"
echo "Python$version is great"

# Maths with $(( ))
result=$((age + 5))
echo "In 5 years: $result"

score=80
percentage=$((score * 100 / 100))
echo "Score: $percentage%"

#!/bin/bash

# Special built-in variables
echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "Number of arguments: $#"
echo "All arguments: $@"

# $? — exit code of the last command (0 = success)
ls /home
echo "Exit code of ls: $?"

ls /nonexistent_folder 2>/dev/null
echo "Exit code of failed ls: $?"

# Command substitution — capture output of a command
current_date=$(date +"%Y-%m-%d")
echo "Today is: $current_date"

current_user=$(whoami)
echo "Running as: $current_user"

file_count=$(ls | wc -l)
echo "Files in folder: $file_count"

# Useful: hostname
machine=$(hostname)
echo "Machine: $machine"

#!/bin/bash

# Basic input
read -p "What is your name? " name
echo "Hello, $name!"

# Input with default value
read -p "Enter your city (default: Cape Town): " city
city=${city:-"Cape Town"}
echo "City: $city"

# Hidden input (for passwords)
read -s -p "Enter your password: " password
echo ""
echo "Password length: ${#password} characters"

# Read multiple values at once
read -p "Enter first and last name: " first last
echo "First: $first"
echo "Last:  $last"

# Read into an array
read -p "Enter three colours: " -a colours
echo "You chose: ${colours[0]}, ${colours[1]}, ${colours[2]}"

#!/bin/bash

score=75

# Basic if/elif/else
if [ $score -ge 80 ]; then
    echo "Grade: A — Excellent!"
elif [ $score -ge 70 ]; then
    echo "Grade: B — Good job!"
elif [ $score -ge 60 ]; then
    echo "Grade: C — Average"
elif [ $score -ge 50 ]; then
    echo "Grade: D — Just passed"
else
    echo "Grade: F — Try again"
fi

# Comparing strings
day="Monday"

if [ "$day" = "Saturday" ] || [ "$day" = "Sunday" ]; then
    echo "It is the weekend!"
else
    echo "$day is a weekday."
fi

# Checking if a variable is empty
username=""

if [ -z "$username" ]; then
    echo "No username provided"
else
    echo "Username: $username"
fi

#!/bin/bash

file="notes.txt"
folder="Documents"

# -e  exists (file or directory)
if [ -e "$file" ]; then
    echo "$file exists"
else
    echo "$file does NOT exist"
fi

# -f  is a regular file (not a directory)
if [ -f "$file" ]; then
    echo "$file is a file"
fi

# -d  is a directory
if [ -d "$folder" ]; then
    echo "$folder is a directory"
fi

# -r  is readable
if [ -r "$file" ]; then
    echo "$file is readable"
fi

# -w  is writable
if [ -w "$file" ]; then
    echo "$file is writable"
fi

# -s  is not empty (has content)
if [ -s "$file" ]; then
    echo "$file has content"
else
    echo "$file is empty"
fi

# Practical: create folder only if it doesn't exist
backup_dir="./backups"
if [ ! -d "$backup_dir" ]; then
    mkdir "$backup_dir"
    echo "Created $backup_dir"
else
    echo "$backup_dir already exists"
fi

#!/bin/bash

read -p "Enter a day (Mon/Tue/Wed...): " day

case "$day" in
    Mon|Monday)
        echo "Start of the work week. Let's go!"
        ;;
    Tue|Tuesday)
        echo "Tuesday — keep the momentum."
        ;;
    Wed|Wednesday)
        echo "Midweek already!"
        ;;
    Thu|Thursday)
        echo "Nearly Friday..."
        ;;
    Fri|Friday)
        echo "TGIF! Almost weekend."
        ;;
    Sat|Saturday|Sun|Sunday)
        echo "Weekend! Time to rest."
        ;;
    *)
        echo "Unknown day: $day"
        ;;
esac

# Case with commands
action="backup"

case "$action" in
    start)   echo "Starting service..." ;;
    stop)    echo "Stopping service..." ;;
    restart) echo "Restarting service..." ;;
    backup)  echo "Running backup now..." ;;
    *)       echo "Unknown action: $action" ;;
esac

#!/bin/bash

# Loop over a list of items
for colour in red green blue yellow; do
    echo "Colour: $colour"
done

echo "---"

# Loop with a number range {start..end}
for i in {1..5}; do
    echo "Count: $i"
done

echo "---"

# Loop with step {start..end..step}
for i in {0..20..5}; do
    echo -n "$i "
done
echo

echo "---"

# C-style for loop
for (( i=1; i<=4; i++ )); do
    echo "Item $i"
done

echo "---"

# Loop over all .txt files in a directory
for file in *.txt; do
    echo "Found text file: $file"
done

#!/bin/bash

# Basic while loop — countdown
count=5
while [ $count -gt 0 ]; do
    echo "$count..."
    count=$((count - 1))
done
echo "Blast off!"

echo "---"

# Validate user input with a loop
while true; do
    read -p "Enter a number between 1-10: " num
    if [ "$num" -ge 1 ] && [ "$num" -le 10 ] 2>/dev/null; then
        echo "Great! You entered: $num"
        break
    else
        echo "Invalid! Please try again."
    fi
done

echo "---"

# continue — skip even numbers
for i in {1..8}; do
    remainder=$((i % 2))
    if [ $remainder -eq 0 ]; then
        continue
    fi
    echo "Odd: $i"
done

#!/bin/bash

# Define a function
greet() {
    echo "Hello, $1!"
    echo "Welcome to the terminal."
}

# Call the function with an argument
greet "Alice"
greet "Bob"

echo "---"

# Function with multiple arguments
introduce() {
    local name=$1
    local age=$2
    local city=$3
    echo "$name is $age years old and lives in $city."
}

introduce "Alice" 25 "Cape Town"
introduce "Bob"   30 "Johannesburg"

echo "---"

# Function that returns a value via echo
add_numbers() {
    local result=$(( $1 + $2 ))
    echo $result
}

sum=$(add_numbers 15 27)
echo "15 + 27 = $sum"

double=$(add_numbers $sum $sum)
echo "Doubled: $double"

#!/bin/bash
# ─────────────────────────────────────────────
# backup.sh — Simple backup script
# Usage: ./backup.sh <source_folder>
# ─────────────────────────────────────────────

# --- Configuration ---
BACKUP_DIR="$HOME/backups"
DATE=$(date +"%Y-%m-%d_%H-%M")

# --- Functions ---

check_args() {
    if [ $# -lt 1 ]; then
        echo "Usage: $0 <folder_to_backup>"
        exit 1
    fi
}

create_backup_dir() {
    if [ ! -d "$BACKUP_DIR" ]; then
        mkdir -p "$BACKUP_DIR"
        echo "Created backup directory: $BACKUP_DIR"
    fi
}

do_backup() {
    local source=$1
    local dest="$BACKUP_DIR/backup_${DATE}.tar.gz"

    echo "Backing up: $source"
    echo "Destination: $dest"

    tar -czf "$dest" "$source" 2>/dev/null
    echo "Backup complete!"
    echo "Size: $(du -sh "$dest" | cut -f1)"
}

# --- Main ---
check_args "$@"
create_backup_dir
do_backup "$1"

#!/bin/bash

# | pipe — chain commands
# Count how many files are in the folder
ls | wc -l

# Find all .sh files and count them
ls *.sh | wc -l

# Sort the output of ls alphabetically
ls | sort

# Search and count matching lines
grep "error" server.log | wc -l

# Chain multiple pipes
cat server.log | grep "ERROR" | sort | uniq

echo "---"

# > Redirect output to a file (creates or overwrites)
echo "Log started" > output.log
date >> output.log
ls -la >> output.log

# Read file contents
cat output.log

echo "---"

# 2> Redirect errors to a file (suppress them)
ls /nonexistent 2>/dev/null
ls /nonexistent 2>errors.log

# Redirect both output AND errors
ls /home /nonexistent > all.log 2>&1

#!/bin/bash

# ── GREP ──────────────────────────────────
# Basic search
grep "Alice" users.txt

# -i  Case insensitive
grep -i "alice" users.txt

# -n  Show line numbers
grep -n "error" server.log

# -c  Count matching lines only
grep -c "error" server.log

# -v  Invert — show NON-matching lines
grep -v "INFO" server.log

# -r  Search recursively in a folder
grep -r "TODO" ./scripts/

# ── SED ───────────────────────────────────
# Replace first occurrence per line
sed 's/error/ERROR/' server.log

# Replace ALL occurrences per line (g flag)
sed 's/http/https/g' urls.txt

# Edit file in place (saves changes to file)
sed -i 's/localhost/production.server.com/g' config.txt

# Delete lines matching a pattern
sed '/^#/d' config.txt

# Print only specific lines (e.g. lines 5-10)
sed -n '5,10p' bigfile.txt

#!/bin/bash

# View permissions with ls -l
ls -l myscript.sh

# chmod — Change file permissions
# Using letters:
chmod +x myscript.sh
chmod +r notes.txt
chmod -w readonly.txt
chmod u+x script.sh
chmod go-w private.sh

# Using numbers (octal):
# 4=read  2=write  1=execute
chmod 755 myscript.sh   # rwxr-xr-x
chmod 644 config.txt    # rw-r--r--
chmod 600 secret.key    # rw-------

ls -l myscript.sh
echo "Script is now executable!"