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Shell Scripting Tutorial for Beginners 🚀

Shell scripting is a powerful way to automate tasks in Linux. This tutorial will cover the basics of shell scripting with examples.

1. What is Shell Scripting?

A shell script is a file containing a series of commands that the shell executes. It helps automate repetitive tasks, system administration, and process automation.

Why Use Shell Scripting?

✅ Automate tasks
✅ Reduce manual errors
✅ Schedule jobs using cron
✅ Process files efficiently

2. Creating Your First Shell Script

Step 1: Create a Script File

bash
nano myscript.sh

Step 2: Add Shell Script Code

bash
#!/bin/bash
echo "Hello, World!"
  • #!/bin/bash → Shebang (tells Linux to use the Bash shell)
  • echo → Prints text to the terminal

Step 3: Give Execute Permission

bash
chmod +x myscript.sh

Step 4: Run the Script

bash
./myscript.sh

Output:

Hello, World!

3. Variables in Shell Scripts

Defining and Using Variables

#!/bin/bash
name="Alice"
echo "Hello, $name!"

Output:

Hello, Alice!

Using Command Substitution

bash
date_today=$(date)
echo "Today's date is $date_today"

4. Taking User Input

bash
#!/bin/bash
echo "Enter your name:"
read user_name
echo "Hello, $user_name!"

Output:

yaml
Enter your name:
John
Hello, John!

5. Conditional Statements

If Statement

#!/bin/bash
echo "Enter a number:"
read numif [ $num -gt 10 ]; then
echo “Number is greater than 10”
else
echo “Number is 10 or less”
fi

6. Loops in Shell Scripting

For Loop

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

While Loop

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

7. Functions in Shell Scripts

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

Output:

Hello, Alice!
Hello, Bob!

8. Working with Files

Check if a File Exists

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

Reading a File Line by Line

#!/bin/bash
while read line; do
echo "Line: $line"
done < myfile.txt

9. Scheduling Scripts with Cron Jobs

To run a script automatically, use cron:

crontab -e

Add a line like:

0 9 * * * /home/user/myscript.sh

(Runs myscript.sh every day at 9 AM)

10. Shell Script Debugging

Run a script with debugging enabled:

bash
bash -x myscript.sh

Conclusion

You have learned the basics of shell scripting, including variables, loops, conditions, functions, and file handling. Shell scripting is widely used in automation, system administration, and DevOps.

Advanced Shell Scripting Tutorial 🚀

Now that you know the basics, let’s dive into more advanced concepts with practical examples.

1. Command-Line Arguments

Shell scripts can accept arguments from the command line.

Example: Using Arguments in a Script

#!/bin/bash
echo "Script Name: $0"
echo "First Argument: $1"
echo "Second Argument: $2"
echo "All Arguments: $@"
echo "Total Arguments: $#"

Usage:

./script.sh Alice Bob

Output:

yaml
Script Name: ./script.sh
First Argument: Alice
Second Argument: Bob
All Arguments: Alice Bob
Total Arguments: 2

2. Using getopts for Argument Parsing

To handle options like -f or -v:

bash
#!/bin/bash
while getopts "n:a:" opt; do
case $opt in
n) name="$OPTARG" ;;
a) age="$OPTARG" ;;
*) echo "Invalid option"; exit 1 ;;
esac
done
echo "Name: $name"
echo "Age: $age"

Usage:

./script.sh -n Alice -a 25

Output:

makefile
Name: Alice
Age: 25

3. Logging and Debugging

Log Script Output to a File

#!/bin/bash
exec > >(tee log.txt) 2>&1
echo "This is a log entry"

Enable Debugging Mode

#!/bin/bash
set -x # Enable debugging
echo "Debugging is ON"
set +x # Disable debugging

4. Handling Signals (trap)

trap allows capturing signals like CTRL+C (SIGINT).

#!/bin/bash
trap "echo 'CTRL+C detected! Exiting...'; exit" SIGINT

while true; do
echo “Running…”
sleep 2
done

Press CTRL+C to see the trap message.

5. Parallel Processing with &

Run multiple tasks in parallel.

#!/bin/bash
echo "Task 1"; sleep 3 & # Runs in the background
echo "Task 2"; sleep 2 & # Runs in the background
wait # Wait for all background processes to finish
echo "All tasks completed"

6. Working with Arrays

#!/bin/bash
fruits=("Apple" "Banana" "Cherry")
echo "First fruit: ${fruits[0]}"
echo "All fruits: ${fruits[@]}"

7. Processing Large Files Efficiently

Instead of using cat file | awk, use:

awk '{print $1}' largefile.txt

Find and Replace in a File

sed -i 's/oldword/newword/g' file.txt

Extract Specific Columns from a CSV

cut -d ',' -f1,3 data.csv

8. Networking with Shell Scripts

Ping Multiple Servers

bash
#!/bin/bash
servers=("google.com" "github.com")

for server in “${servers[@]}“; do
ping -c 2 $server && echo “$server is reachable” || echo “$server is down”
done

Download a File Using wget

bash
wget -O downloaded_file.zip "https://example.com/file.zip"

9. Automating Backups

bash
#!/bin/bash
backup_dir="/backup"
mkdir -p $backup_dir
tar -czf "$backup_dir/backup_$(date +%F).tar.gz" /home/user
echo "Backup completed!"

10. Scheduling Jobs with cron

Edit the crontab:

crontab -e

Run a script every day at midnight:

0 0 * * * /home/user/backup.sh