Bash Hello World

#!/bin/bash
echo "Hello, World!"

Output:

Hello, World!

Variables

NAME="John"
AGE=30
echo "My name is $NAME and I am $AGE years old."

Output:

My name is John and I am 30 years old.

Conditional Statements

NUM=10
if [ $NUM -eq 10 ]; then
  echo "Number is 10."
elif [ $NUM -gt 10 ]; then
  echo "Number is greater than 10."
else
  echo "Number is less than 10."
fi

Output:

Number is 10.

Loops

For Loop

for i in {1..5}; do
  echo "Iteration $i"
done

Output:

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

While Loop

COUNT=0
while [ $COUNT -lt 5 ]; do
  echo "Count: $COUNT"
  ((COUNT++))
done

Output:

Count: 0
Count: 1
Count: 2
Count: 3
Count: 4

Functions

say_hello() {
  echo "Hello, $1!"
}

say_hello "Alice"

Output:

Hello, Alice!

Arithmetic

NUM1=20
NUM2=5
echo "Addition: $((NUM1 + NUM2))"
echo "Subtraction: $((NUM1 - NUM2))"
echo "Multiplication: $((NUM1 * NUM2))"
echo "Division: $((NUM1 / NUM2))"
echo "Modulus: $((NUM1 % NUM2))"

Output:

Addition: 25
Subtraction: 15
Multiplication: 100
Division: 4
Modulus: 0

Arrays

FRUITS=("Apple" "Banana" "Cherry")
echo "First fruit: ${FRUITS[0]}"
echo "All fruits: ${FRUITS[@]}"

Output:

First fruit: Apple
All fruits: Apple Banana Cherry

Bash Arguments

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

Output (assuming script is named script.sh and executed with arguments arg1 and arg2):

First argument: arg1
Second argument: arg2

Input

echo "Enter your name:"
read NAME
echo "Hello, $NAME!"

Output (assuming user inputs Alice):

Enter your name:
Alice
Hello, Alice!

Concatenate Strings

STR1="Hello"
STR2="World"
echo "$STR1 $STR2"

Output:

Hello World

Debugging

set -x  # Start debugging from here
NUM=15
if [ $NUM -lt 10 ]; then
  echo "Number is less than 10."
else
  echo "Number is greater than or equal to 10."
fi
set +x  # Stop debugging

Output:

+ NUM=15
+ '[' 15 -lt 10 ']'
+ echo 'Number is greater than or equal to 10.'
Number is greater than or equal to 10.

Comments

# This is a comment
echo "This line is executed."

Output:

This line is executed.

Read Files

while IFS= read -r line; do
  echo "Line: $line"
done < "file.txt"

Output (assuming file.txt contains lines Line 1 and Line 2):

Line: Line 1
Line: Line 2

Redirections

echo "Hello" > output.txt  # Redirect stdout to a file
cat < input.txt  # Redirect input from a file

Output:

(No output displayed for redirection examples)

Switch-Case Statements

FRUIT="Apple"
case $FRUIT in
  "Apple")
    echo "Selected fruit is Apple."
    ;;
  "Banana")
    echo "Selected fruit is Banana."
    ;;
  "Cherry")
    echo "Selected fruit is Cherry."
    ;;
  *)
    echo "Unknown fruit."
    ;;
esac

Output:

Selected fruit is Apple.

This tutorial now includes a section on switch-case statements (case) in Bash, demonstrating how to use it with example code and showing the expected output or behavior.