Linux Bash Scriptsl

🎯 Objective

Learn how to create, write, and execute Bash scripts in Linux to automate tasks such as running commands, managing files, and scheduling operations.

# 📘 What is a Bash Script?

A Bash script is a file containing a series of commands that the Bash shell executes sequentially.

Instead of typing commands one by one in the terminal, you can automate them inside a script.

Example use cases:

# 📂 Script File Extension

Most Bash scripts use the extension:

.sh

Example:

backup.sh
deploy.sh
monitor.sh

Note: The extension is not required but helps readability.

# What is scp?🔹

scp (secure copy) = copy files between servers over SSH

👉 Think of it like:

🔹 Basic Syntax

scp <source> <user>@<host>:<destination>

# 🧾 Basic Bash Script Structure

Example:

#!/bin/bash

echo"Hello, Linux!"

Explanation:

# 🛠 Creating a Bash Script

Step 1: Create file

nano hello.sh

or

vi hello.sh

Step 2: Add script code

#!/bin/bash

echo"Welcome to Linux Bash scripting"

Step 3: Save the file

Step 4: Give execute permission

chmod+x hello.sh

Step 5: Run the script

Method 1:

./hello.sh

Method 2:

bash hello.sh

# 📜 Script Execution Permission

In Linux, a file must have execute (x) permission to run as a program.

Check permissions:

ls-l hello.sh

Example output:

-rwxr-xr-x 1 user user 120 Mar 16 hello.sh

Explanation:

# 📥 Variables in Bash

Variables store values.

Example:

#!/bin/bash

name="Linux User"
echo"Hello$name"

Output:

Hello Linux User

# 📨 User Input in Bash

Use read to accept input from user.

Example:

#!/bin/bash

echo"Enter your name:"
read name

echo"Hello$name"

# 🔀 Conditional Statements

If Statement

#!/bin/bash

number=10

if [$number-gt5 ]
then
echo"Number is greater than 5"
fi

Common operators:

# 🔁 Loops in Bash

For Loop

#!/bin/bash

for iin12345
do
echo"Number:$i"
done

While Loop

#!/bin/bash

count=1

while [$count-le5 ]
do
echo"Count:$count"
count=$((count+1))
done

# 📁 Working With Files in Scripts

Check if file exists

if [-f"file.txt" ]
then
echo"File exists"
else
echo"File not found"
fi

Create a file

touch test.txt

Delete a file

rm test.txt

# 📦 Useful Bash Commands for Scripts

# 🧪 Example Script: System Information

#!/bin/bash

echo"System Information"
echo"-------------------"

echo"User:$(whoami)"
echo"Hostname:$(hostname)"
echo"Date:$(date)"
echo"Uptime:"
uptime

Run:

./systeminfo.sh

# ⚠ Common Bash Script Errors

Permission denied

Error:

permission denied

Fix:

chmod+x script.sh

Wrong interpreter

Error occurs if shebang is missing.

Correct:

#!/bin/bash

Syntax errors

Example:

Missing fi

if [$x-gt5 ]
then
echo"test"

Correct:

if [$x-gt5 ]
then
echo"test"
fi

# 🛠 Debugging Bash Scripts

Run script in debug mode:

bash-x script.sh

This shows each command before execution.

# 🧾 Example: Backup Script

#!/bin/bash

backup_dir="/backup"
source_dir="/home"

echo"Starting backup..."

tar-czf$backup_dir/home_backup.tar.gz$source_dir

echo"Backup completed."

# 🔄 Automating Scripts with Cron

Example cron job:

02 * * * /home/user/backup.sh

Meaning:

Run backup script every day at 2 AM.

# ✅ Key Learning Points