Bash Programming Examples

Example 1: Hello World

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

Hello, World!

The most basic Bash script that prints "Hello, World!" to the terminal.

Example 2: Variables

#!/bin/bash
name="John"
age=25
echo "My name is $name and I am $age years old."

My name is John and I am 25 years old.

Demonstrates how to declare and use variables in Bash.

Example 3: Command Substitution

#!/bin/bash
current_date=$(date)
echo "Current date and time: $current_date"

Current date and time: Wed Aug 25 14:32:15 UTC 2021

Shows how to capture the output of a command and store it in a variable.

Example 4: User Input

#!/bin/bash
echo "What's your name?"
read name
echo "Hello, $name!"

What's your name?
Alice
Hello, Alice!

Reads input from the user and uses it in the script.

Example 5: If Statement

#!/bin/bash
number=10
if [ $number -eq 10 ]; then
echo "The number is 10"
fi

The number is 10

Basic conditional statement that checks if a variable equals 10.

Example 6: If-Else Statement

#!/bin/bash
number=15
if [ $number -lt 10 ]; then
echo "Number is less than 10"
else
echo "Number is greater than or equal to 10"
fi

Number is greater than or equal to 10

Demonstrates if-else conditional logic in Bash.

Example 7: For Loop

#!/bin/bash
for i in 1 2 3 4 5; do
echo "Number: $i"
done

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Basic for loop that iterates through a list of numbers.

Example 8: While Loop

#!/bin/bash
count=1
while [ $count -le 5 ]; do
echo "Count: $count"
count=$((count + 1))
done

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

A while loop that runs as long as the condition is true.

Example 9: Functions

#!/bin/bash
greet() {
echo "Hello, $1!"
}

greet "Alice"
greet "Bob"

Hello, Alice!
Hello, Bob!

Defines and calls a simple function that takes a parameter.

Example 10: Arithmetic Operations

#!/bin/bash
a=10
b=3

echo "Addition: $((a + b))"
echo "Subtraction: $((a - b))"
echo "Multiplication: $((a * b))"
echo "Division: $((a / b))"
echo "Modulus: $((a % b))"

Addition: 13
Subtraction: 7
Multiplication: 30
Division: 3
Modulus: 1

Performs basic arithmetic operations using Bash.

Example 11: File Existence Check

#!/bin/bash
file="example.txt"
if [ -f "$file" ]; then
echo "$file exists."
else
echo "$file does not exist."
fi

example.txt does not exist.

Checks if a file exists using the -f flag.

Example 12: String Comparison

#!/bin/bash
str1="Hello"
str2="World"

if [ "$str1" = "$str2" ]; then
echo "Strings are equal"
else
echo "Strings are not equal"
fi

Strings are not equal

Compares two strings for equality.

Example 13: Case Statement

#!/bin/bash
fruit="apple"

case $fruit in
  "apple") echo "It's an apple.";;
  "banana") echo "It's a banana.";;
  *) echo "It's something else.";;
esac

It's an apple.

Uses a case statement to match against different patterns.

Example 14: Command Line Arguments

#!/bin/bash
echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "Total arguments: $#"

Script name: ./script.sh
First argument: arg1
Second argument: arg2
Total arguments: 2

Accesses command line arguments passed to the script.

Example 15: Arrays

#!/bin/bash
fruits=("Apple" "Banana" "Orange")

echo "First fruit: ${fruits[0]}"
echo "All fruits: ${fruits[@]}"
echo "Number of fruits: ${#fruits[@]}"

First fruit: Apple
All fruits: Apple Banana Orange
Number of fruits: 3

Demonstrates how to create and use arrays in Bash.

Example 16: Reading a File Line by Line

#!/bin/bash
while IFS= read -r line; do
echo "Line: $line"
done < "example.txt"

Line: This is line 1
Line: This is line 2
Line: This is line 3

Reads a file line by line and processes each line.

Example 17: Sleep Command

#!/bin/bash
echo "Starting..."
sleep 2
echo "After 2 seconds"

Starting...
[2 second pause]
After 2 seconds

Pauses the script execution for a specified number of seconds.

Example 18: Exit Codes

#!/bin/bash
ls /nonexistentdirectory
echo "Exit code: $?"

ls: cannot access '/nonexistentdirectory': No such file or directory
Exit code: 2

Checks the exit code of the previous command.

Example 19: String Operations

#!/bin/bash
str="Hello World"

echo "Length: ${#str}"
echo "Uppercase: ${str^^}"
echo "Lowercase: ${str,,}"
echo "Substring: ${str:6:5}"

Length: 11
Uppercase: HELLO WORLD
Lowercase: hello world
Substring: World

Demonstrates various string manipulation operations.

Example 20: Debugging with set -x

#!/bin/bash
set -x

a=5
b=3
result=$((a + b))
echo "Result: $result"

set +x
echo "Debugging turned off"

+ a=5
+ b=3
+ result=8
+ echo 'Result: 8'
Result: 8
+ set +x
Debugging turned off

Shows how to enable and disable debugging in Bash scripts.

Example 21: Using bc for Floating Point

#!/bin/bash
a=10
b=3

echo "Scale=2; $a / $b" | bc

3.33

Uses the bc calculator for floating-point arithmetic.

Example 22: Here Document

#!/bin/bash
cat << EOF
This is a multiline
string using a here document
It can contain variables like $(date)
EOF

This is a multiline
string using a here document
It can contain variables like Wed Aug 25 14:32:15 UTC 2021

Uses a here document to output multiline text.

Example 23: Redirecting Output

#!/bin/bash
echo "This goes to stdout"
echo "This goes to stderr" >&2
echo "This goes to a file" > output.txt

This goes to stdout
This goes to stderr

Demonstrates output redirection to different destinations.

Example 24: Using grep in Script

#!/bin/bash
echo -e "apple\nbanana\norange" > fruits.txt
grep "na" fruits.txt

banana
orange

Uses grep to search for patterns in a file.

Example 25: Simple Calculator

#!/bin/bash
add() {
echo $(($1 + $2))
}

result=$(add 5 3)
echo "5 + 3 = $result"

5 + 3 = 8

A simple calculator function that adds two numbers.