---

🔧 1. Shebang (Always First Line)

#!/bin/bash

Tells the system to run the script using the Bash shell.

---

💬 2. Comments

# This is a comment

Everything after # is ignored by the shell.

---

📄 3. Variables

name="John"
echo "Hello, $name"

• No space around =.
• Use $name to access the value.

---

🧮 4. Arithmetic

x=5
y=3
sum=$((x + y))
echo "Sum: $sum"

Use $(( )) for arithmetic operations.

---

🎛️ 5. Conditionals

If-Else

if [ "$name" == "John" ]; then
    echo "Hello John"
else
    echo "You're not John"
fi

Operators inside [ ]:

• ==, != for strings
• -eq, -ne, -gt, -lt, -ge, -le for numbers

---

🔁 6. Loops

For Loop

for i in 1 2 3; do
    echo "Number $i"
done

While Loop

count=1
while [ $count -le 3 ]; do
    echo "Count is $count"
    ((count++))
done

---

📦 7. Functions

greet() {
    echo "Hello, $1"
}

greet "Alice"

• $1, $2, etc., are positional arguments.

---

🔀 8. Command Substitution

today=$(date)
echo "Today is $today"

• Runs a command and stores the output in a variable.

---

📂 9. File/Directory Checks

if [ -f "file.txt" ]; then
    echo "file.txt exists"
fi

if [ -d "/etc" ]; then
    echo "/etc is a directory"
fi

---

🔢 10. Script Arguments

echo "First arg: $1"
echo "Second arg: $2"

Call with:

./myscript.sh hello world

---

🧼 11. Exit and Return Values

exit 0  # Success
exit 1  # Error

---

🛠️ Useful Shortcuts

Syntax	Meaning
$(command)	Run command and get output
$?	Exit code of last command
$#	Number of arguments
$@ or $*	All arguments

---