Shell scriptting

50 Beginner-Friendly Bash Shell Script Examples for System Administrators

This guide contains 50 basic Bash shell scripting examples designed for beginners and junior Linux/System Administrators.

Topics covered:

Command-line parameters: $0, $1, $2, $#, $@, $*
Exit status: $?
Process IDs: $$, $!
if, if-else, and elif
for loops
while loops
until loops
case statements
select keyboard menus
Functions
Files, directories, users, services, disks, memory, and logs
Basic system administration automation

Important: Some system administration scripts require sudo or root access.

How to Use These Examples

Create a file:

vi script.sh

Add the script content, save it, and make it executable:

chmod +x script.sh

Run it:

./script.sh

You can also run a Bash script without executable permission:

bash script.sh

Part 1 — Parameters and Special Variables

1. Display Script Name and Parameters

Purpose: Learn $0, $1, $2, and $3.

#!/bin/bash

echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "Third argument: $3"

Run:

./parameters.sh Linux Docker Kubernetes

Output:

Script name: ./parameters.sh
First argument: Linux
Second argument: Docker
Third argument: Kubernetes

2. Count the Number of Arguments

Purpose: $# gives the total number of command-line arguments.

#!/bin/bash

echo "Number of arguments: $#"

Run:

./count-args.sh one two three four

Output:

Number of arguments: 4

3. Display All Arguments Using `$@`

Purpose: "$@" treats every parameter as a separate value.

#!/bin/bash

echo "All arguments:"

for argument in "$@"
do
    echo "$argument"
done

Run:

./all-args.sh Linux "Red Hat" Ubuntu

Output:

All arguments:
Linux
Red Hat
Ubuntu

4. Difference Between `$*` and `$@`

#!/bin/bash

echo 'Using "$*":'

for argument in "$*"
do
    echo "$argument"
done

echo 'Using "$@":'

for argument in "$@"
do
    echo "$argument"
done

Run:

./star-vs-at.sh Linux Docker Kubernetes

Output:

Using "$*":
Linux Docker Kubernetes

Using "$@":
Linux
Docker
Kubernetes

Interview point: Prefer "$@" when processing arguments.

5. Validate the Number of Arguments

#!/bin/bash

if [ "$#" -ne 2 ]
then
    echo "Usage: $0 <username> <department>"
    exit 1
fi

echo "Username: $1"
echo "Department: $2"

Run correctly:

./validate.sh sreejith devops

Output:

Username: sreejith
Department: devops

Run incorrectly:

./validate.sh sreejith

Output:

Usage: ./validate.sh <username> <department>

6. Check the Exit Status Using `$?`

#!/bin/bash

ls /etc/passwd

echo "Exit status: $?"

Output:

/etc/passwd
Exit status: 0

A successful command normally returns 0. A failed command returns a non-zero value.

7. Check Whether a Command Succeeded

#!/bin/bash

ping -c 1 8.8.8.8 > /dev/null 2>&1

if [ "$?" -eq 0 ]
then
    echo "Network is reachable."
else
    echo "Network is not reachable."
fi

8. Display the Current Script Process ID

Purpose: $$ contains the PID of the current script.

#!/bin/bash

echo "Current script PID: $$"

Example output:

Current script PID: 24510

9. Display the Last Background Process ID

Purpose: $! contains the PID of the most recently started background process.

#!/bin/bash

sleep 30 &

echo "Background process PID: $!"

10. Use `shift` to Process Parameters

shift removes the first argument and moves the remaining arguments left.

#!/bin/bash

while [ "$#" -gt 0 ]
do
    echo "Current argument: $1"
    shift
done

Run:

./shift-example.sh server1 server2 server3

Output:

Current argument: server1
Current argument: server2
Current argument: server3

Part 2 — Conditions

11. Check Whether a File Exists

#!/bin/bash

file_name="$1"

if [ -f "$file_name" ]
then
    echo "$file_name exists and is a regular file."
else
    echo "$file_name does not exist."
fi

Run:

./check-file.sh /etc/passwd

12. Check Whether a Directory Exists

#!/bin/bash

directory="$1"

if [ -d "$directory" ]
then
    echo "$directory exists."
else
    echo "$directory does not exist."
fi

Run:

./check-directory.sh /var/log

13. Create a Directory Only If It Does Not Exist

#!/bin/bash

directory="$1"

if [ -z "$directory" ]
then
    echo "Usage: $0 <directory>"
    exit 1
fi

if [ -d "$directory" ]
then
    echo "Directory already exists: $directory"
else
    mkdir -p "$directory"

    if [ "$?" -eq 0 ]
    then
        echo "Directory created: $directory"
    else
        echo "Failed to create directory."
        exit 1
    fi
fi

14. Compare Two Numbers

#!/bin/bash

number1="$1"
number2="$2"

if [ "$number1" -gt "$number2" ]
then
    echo "$number1 is greater than $number2"
elif [ "$number1" -lt "$number2" ]
then
    echo "$number1 is less than $number2"
else
    echo "Both numbers are equal."
fi

15. Check Whether a Number Is Even or Odd

#!/bin/bash

number="$1"

if [ $((number % 2)) -eq 0 ]
then
    echo "$number is even."
else
    echo "$number is odd."
fi

Run:

./even-odd.sh 15

Output:

15 is odd.

16. Check Whether a String Is Empty

#!/bin/bash

read -r -p "Enter your name: " name

if [ -z "$name" ]
then
    echo "You did not enter a name."
else
    echo "Hello, $name"
fi

17. Compare Two Strings

#!/bin/bash

read -r -p "Enter environment: " environment

if [ "$environment" = "production" ]
then
    echo "Production environment selected."
else
    echo "Non-production environment selected."
fi

18. Check Whether the Current User Is Root

#!/bin/bash

if [ "$EUID" -eq 0 ]
then
    echo "You are running as root."
else
    echo "Run this script using sudo."
    exit 1
fi

19. Check Whether a User Exists

#!/bin/bash

username="$1"

if id "$username" > /dev/null 2>&1
then
    echo "User exists: $username"
else
    echo "User does not exist: $username"
fi

Run:

./check-user.sh root

20. Check Whether a Service Is Active

#!/bin/bash

service_name="$1"

if systemctl is-active --quiet "$service_name"
then
    echo "$service_name is running."
else
    echo "$service_name is not running."
fi

Run:

./check-service.sh ssh

On RHEL-based systems, the SSH service is usually named sshd.

Part 3 — `for` Loops

21. Basic `for` Loop

#!/bin/bash

for item in Linux Docker Kubernetes Ansible
do
    echo "Technology: $item"
done

22. Loop Through Numbers

#!/bin/bash

for number in {1..10}
do
    echo "Number: $number"
done

23. C-Style `for` Loop

#!/bin/bash

for ((number=1; number<=5; number++))
do
    echo "Iteration: $number"
done

24. Loop Through Files in a Directory

#!/bin/bash

directory="/var/log"

for file in "$directory"/*
do
    echo "Found: $file"
done

25. Display the Size of Every Log File

#!/bin/bash

for file in /var/log/*.log
do
    if [ -f "$file" ]
    then
        size=$(du -h "$file" | awk '{print $1}')
        echo "$file : $size"
    fi
done

26. Ping Multiple Servers

#!/bin/bash

servers=("8.8.8.8" "1.1.1.1" "192.168.0.1")

for server in "${servers[@]}"
do
    if ping -c 1 -W 2 "$server" > /dev/null 2>&1
    then
        echo "$server is reachable."
    else
        echo "$server is unreachable."
    fi
done

27. Read Server Names from a File

Create servers.txt:

server1
server2
server3

Script:

#!/bin/bash

while IFS= read -r server
do
    echo "Processing server: $server"
done < servers.txt

28. Create Multiple Directories

#!/bin/bash

for directory in backup logs reports scripts
do
    mkdir -p "$directory"
    echo "Created directory: $directory"
done

29. Create Multiple Users from Parameters

#!/bin/bash

if [ "$#" -eq 0 ]
then
    echo "Usage: $0 <user1> <user2> ..."
    exit 1
fi

for username in "$@"
do
    if id "$username" > /dev/null 2>&1
    then
        echo "User already exists: $username"
    else
        sudo useradd "$username"

        if [ "$?" -eq 0 ]
        then
            echo "Created user: $username"
        else
            echo "Failed to create user: $username"
        fi
    fi
done

Test user-management scripts only in a lab system.

30. Find Large Files

#!/bin/bash

directory="${1:-/var/log}"
size="${2:-100M}"

echo "Files larger than $size in $directory:"

find "$directory" -type f -size +"$size" -exec ls -lh {} \; 2>/dev/null

Run:

./large-files.sh /var 50M

Part 4 — `while` and `until` Loops

31. Basic `while` Loop

#!/bin/bash

counter=1

while [ "$counter" -le 5 ]
do
    echo "Counter: $counter"
    counter=$((counter + 1))
done

32. Countdown Using `while`

#!/bin/bash

counter=5

while [ "$counter" -gt 0 ]
do
    echo "$counter"
    sleep 1
    counter=$((counter - 1))
done

echo "Completed."

33. Read User Input Until `exit`

#!/bin/bash

while true
do
    read -r -p "Enter a command or type exit: " command

    if [ "$command" = "exit" ]
    then
        echo "Exiting."
        break
    fi

    echo "You entered: $command"
done

34. Monitor Disk Usage Continuously

#!/bin/bash

while true
do
    clear
    echo "Disk usage at $(date)"
    df -h
    sleep 10
done

Stop it using:

Ctrl+C

35. Wait Until a Service Starts

#!/bin/bash

service_name="$1"

if [ -z "$service_name" ]
then
    echo "Usage: $0 <service-name>"
    exit 1
fi

until systemctl is-active --quiet "$service_name"
do
    echo "Waiting for $service_name to start..."
    sleep 5
done

echo "$service_name is now running."

36. Wait Until a Host Becomes Reachable

#!/bin/bash

host="$1"

if [ -z "$host" ]
then
    echo "Usage: $0 <hostname-or-ip>"
    exit 1
fi

until ping -c 1 -W 2 "$host" > /dev/null 2>&1
do
    echo "Waiting for $host..."
    sleep 5
done

echo "$host is reachable."

37. Retry a Command Three Times

#!/bin/bash

attempt=1
maximum_attempts=3

while [ "$attempt" -le "$maximum_attempts" ]
do
    echo "Attempt $attempt of $maximum_attempts"

    curl -fsS https://example.com > /dev/null

    if [ "$?" -eq 0 ]
    then
        echo "Command succeeded."
        exit 0
    fi

    attempt=$((attempt + 1))
    sleep 2
done

echo "Command failed after $maximum_attempts attempts."
exit 1

38. Read a File Line by Line

#!/bin/bash

file_name="$1"

if [ ! -f "$file_name" ]
then
    echo "File not found: $file_name"
    exit 1
fi

while IFS= read -r line
do
    echo "$line"
done < "$file_name"

Part 5 — `case` and Keyboard Menus

39. Basic `case` Statement

#!/bin/bash

read -r -p "Enter start, stop, restart, or status: " action

case "$action" in
    start)
        echo "Starting service..."
        ;;
    stop)
        echo "Stopping service..."
        ;;
    restart)
        echo "Restarting service..."
        ;;
    status)
        echo "Checking service status..."
        ;;
    *)
        echo "Invalid option."
        ;;
esac

40. Service Management with `case`

#!/bin/bash

service_name="$1"
action="$2"

if [ "$#" -ne 2 ]
then
    echo "Usage: $0 <service-name> <start|stop|restart|status>"
    exit 1
fi

case "$action" in
    start)
        sudo systemctl start "$service_name"
        ;;
    stop)
        sudo systemctl stop "$service_name"
        ;;
    restart)
        sudo systemctl restart "$service_name"
        ;;
    status)
        systemctl status "$service_name"
        ;;
    *)
        echo "Invalid action: $action"
        exit 1
        ;;
esac

Run:

./service-control.sh ssh status

41. Check Operating System Using `case`

#!/bin/bash

if [ -f /etc/os-release ]
then
    . /etc/os-release
else
    echo "Cannot identify the operating system."
    exit 1
fi

case "$ID" in
    ubuntu|debian)
        echo "Debian-based system detected."
        ;;
    rhel|centos|rocky|almalinux|fedora)
        echo "Red Hat-based system detected."
        ;;
    *)
        echo "Other Linux distribution detected: $ID"
        ;;
esac

42. Simple Keyboard Menu Using `select`

#!/bin/bash

PS3="Select an option: "

select option in "Show date" "Show users" "Show disk usage" "Exit"
do
    case "$option" in
        "Show date")
            date
            ;;
        "Show users")
            who
            ;;
        "Show disk usage")
            df -h
            ;;
        "Exit")
            echo "Goodbye."
            break
            ;;
        *)
            echo "Invalid selection."
            ;;
    esac
done

The user selects an option by entering its number.

43. System Administration Menu

#!/bin/bash

while true
do
    echo
    echo "===== System Administration Menu ====="
    echo "1. Show hostname"
    echo "2. Show IP addresses"
    echo "3. Show disk usage"
    echo "4. Show memory usage"
    echo "5. Show logged-in users"
    echo "6. Exit"

    read -r -p "Enter your choice: " choice

    case "$choice" in
        1)
            hostname
            ;;
        2)
            hostname -I
            ;;
        3)
            df -h
            ;;
        4)
            free -h
            ;;
        5)
            who
            ;;
        6)
            echo "Exiting."
            break
            ;;
        *)
            echo "Invalid choice."
            ;;
    esac
done

Part 6 — Functions and System Administration Scripts

44. Basic Function

#!/bin/bash

show_system_info() {
    echo "Hostname: $(hostname)"
    echo "Kernel: $(uname -r)"
    echo "Current user: $(whoami)"
}

show_system_info

45. Function with Parameters

#!/bin/bash

check_file() {
    local file_name="$1"

    if [ -f "$file_name" ]
    then
        echo "File exists: $file_name"
        return 0
    else
        echo "File not found: $file_name"
        return 1
    fi
}

check_file "/etc/passwd"

echo "Function return status: $?"

46. Disk Usage Alert

#!/bin/bash

threshold="${1:-80}"

usage=$(df / | awk 'NR==2 {gsub("%", "", $5); print $5}')

echo "Root filesystem usage: ${usage}%"

if [ "$usage" -ge "$threshold" ]
then
    echo "WARNING: Disk usage is above ${threshold}%."
    exit 1
else
    echo "Disk usage is normal."
fi

Run:

./disk-alert.sh 75

47. Memory Usage Report

#!/bin/bash

total_memory=$(free -m | awk '/Mem:/ {print $2}')
used_memory=$(free -m | awk '/Mem:/ {print $3}')
free_memory=$(free -m | awk '/Mem:/ {print $4}')
usage_percent=$((used_memory * 100 / total_memory))

echo "Total memory: ${total_memory} MB"
echo "Used memory: ${used_memory} MB"
echo "Free memory: ${free_memory} MB"
echo "Memory usage: ${usage_percent}%"

48. Backup a Directory

#!/bin/bash

source_directory="$1"
backup_directory="$2"
timestamp=$(date +"%Y%m%d_%H%M%S")

if [ "$#" -ne 2 ]
then
    echo "Usage: $0 <source-directory> <backup-directory>"
    exit 1
fi

if [ ! -d "$source_directory" ]
then
    echo "Source directory does not exist: $source_directory"
    exit 1
fi

mkdir -p "$backup_directory"

archive_name="$backup_directory/backup_$timestamp.tar.gz"

tar -czf "$archive_name" "$source_directory"

if [ "$?" -eq 0 ]
then
    echo "Backup created successfully: $archive_name"
else
    echo "Backup failed."
    exit 1
fi

Run:

./backup.sh /etc /tmp/backups

49. Delete Old Log Files

#!/bin/bash

log_directory="${1:-/var/log/myapp}"
retention_days="${2:-30}"

if [ ! -d "$log_directory" ]
then
    echo "Directory not found: $log_directory"
    exit 1
fi

echo "Files older than $retention_days days:"

find "$log_directory" -type f -mtime +"$retention_days" -print

read -r -p "Delete these files? Type yes to continue: " confirmation

if [ "$confirmation" = "yes" ]
then
    find "$log_directory" -type f -mtime +"$retention_days" -delete
    echo "Old files deleted."
else
    echo "Deletion cancelled."
fi

Review the find output carefully before deleting files.

50. Complete Beginner System Health Check

#!/bin/bash

output_file="/tmp/system_health_$(date +%Y%m%d_%H%M%S).txt"

{
    echo "======================================"
    echo "       SYSTEM HEALTH CHECK"
    echo "======================================"
    echo "Date: $(date)"
    echo "Hostname: $(hostname)"
    echo "Current user: $(whoami)"
    echo

    echo "----- Operating System -----"
    if [ -f /etc/os-release ]
    then
        grep -E '^(NAME|VERSION)=' /etc/os-release
    fi
    echo

    echo "----- Kernel -----"
    uname -r
    echo

    echo "----- Uptime -----"
    uptime
    echo

    echo "----- IP Addresses -----"
    hostname -I
    echo

    echo "----- Disk Usage -----"
    df -h
    echo

    echo "----- Memory Usage -----"
    free -h
    echo

    echo "----- Top CPU Processes -----"
    ps -eo pid,user,%cpu,%mem,comm --sort=-%cpu | head
    echo

    echo "----- Top Memory Processes -----"
    ps -eo pid,user,%cpu,%mem,comm --sort=-%mem | head
    echo

    echo "----- Logged-In Users -----"
    who
    echo

    echo "----- Failed Services -----"
    systemctl --failed --no-pager
    echo

    echo "Report completed."
} | tee "$output_file"

echo
echo "Report saved to: $output_file"

Important Bash Test Operators

File Test Operators

Operator	Meaning
`-f file`	File exists and is a regular file
`-d directory`	Directory exists
`-e path`	File or directory exists
`-r file`	File is readable
`-w file`	File is writable
`-x file`	File is executable
`-s file`	File exists and is not empty
`! condition`	Negates a condition

Example:

if [ -r /etc/passwd ]
then
    echo "The file is readable."
fi

Numeric Comparison Operators

Operator	Meaning
`-eq`	Equal
`-ne`	Not equal
`-gt`	Greater than
`-ge`	Greater than or equal
`-lt`	Less than
`-le`	Less than or equal

Example:

if [ "$age" -ge 18 ]
then
    echo "Adult"
fi

String Comparison Operators

Operator	Meaning
`=`	Strings are equal
`!=`	Strings are not equal
`-z string`	String is empty
`-n string`	String is not empty

Important Special Variables

Variable	Meaning
`$0`	Script name
`$1`	First argument
`$2`	Second argument
`${10}`	Tenth argument
`$#`	Number of arguments
`"$@"`	All arguments as separate values
`"$*"`	All arguments as one value
`$?`	Exit status of the previous command
`$$`	PID of the current shell/script
`$!`	PID of the last background process

Important Loop Control Commands

Command	Purpose
`break`	Exit the loop
`continue`	Skip the current iteration
`exit 0`	End the script successfully
`exit 1`	End the script with an error
`shift`	Remove the first positional parameter

Basic Script Template for Beginners

#!/bin/bash

set -u

usage() {
    echo "Usage: $0 <argument>"
}

if [ "$#" -ne 1 ]
then
    usage
    exit 1
fi

value="$1"

echo "Processing: $value"

if [ -e "$value" ]
then
    echo "The path exists."
else
    echo "The path does not exist."
    exit 1
fi

exit 0

Common Beginner Mistakes

1. Missing Spaces Around `[` and `]`

Incorrect:

if ["$name" = "admin"]

Correct:

if [ "$name" = "admin" ]

2. Not Quoting Variables

Risky:

rm $file

Better:

rm -- "$file"

3. Using `$10` Instead of `${10}`

Incorrect:

echo "$10"

This may be interpreted as ${1}0.

Correct:

echo "${10}"

4. Checking `$?` Too Late

Incorrect:

cp source destination
echo "Copy completed"
if [ "$?" -eq 0 ]

$? now contains the status of echo, not cp.

Better:

if cp source destination
then
    echo "Copy completed."
else
    echo "Copy failed."
fi

5. Running Destructive Commands Without Validation

Always validate variables before using commands such as:

rm -rf
find -delete
userdel
shutdown
reboot

Practice Tasks

After completing the examples, try writing scripts that:

Check whether three services are running.
Display files larger than 500 MB.
Alert when memory usage exceeds 80%.
Create five users from a text file.
Back up /etc and keep only seven backups.
Display listening TCP ports.
Check whether a website returns HTTP status 200.
Restart a service when it is inactive.
Display the ten largest directories under /var.
Build a keyboard-based user and service management menu.

50 Beginner-Friendly Bash Shell Script Examples for System Administrators

How to Use These Examples

Part 1 — Parameters and Special Variables

1. Display Script Name and Parameters

2. Count the Number of Arguments

3. Display All Arguments Using $@

4. Difference Between $* and $@

5. Validate the Number of Arguments

6. Check the Exit Status Using $?

7. Check Whether a Command Succeeded

8. Display the Current Script Process ID

9. Display the Last Background Process ID

10. Use shift to Process Parameters

Part 2 — Conditions

11. Check Whether a File Exists

12. Check Whether a Directory Exists

13. Create a Directory Only If It Does Not Exist

14. Compare Two Numbers

15. Check Whether a Number Is Even or Odd

16. Check Whether a String Is Empty

17. Compare Two Strings

18. Check Whether the Current User Is Root

19. Check Whether a User Exists

20. Check Whether a Service Is Active

Part 3 — for Loops

21. Basic for Loop

22. Loop Through Numbers

23. C-Style for Loop

24. Loop Through Files in a Directory

25. Display the Size of Every Log File

26. Ping Multiple Servers

27. Read Server Names from a File

28. Create Multiple Directories

29. Create Multiple Users from Parameters

30. Find Large Files

Part 4 — while and until Loops

31. Basic while Loop

32. Countdown Using while

33. Read User Input Until exit

34. Monitor Disk Usage Continuously

35. Wait Until a Service Starts

36. Wait Until a Host Becomes Reachable

37. Retry a Command Three Times

38. Read a File Line by Line

Part 5 — case and Keyboard Menus

39. Basic case Statement

40. Service Management with case

41. Check Operating System Using case

42. Simple Keyboard Menu Using select

43. System Administration Menu

Part 6 — Functions and System Administration Scripts

44. Basic Function

45. Function with Parameters

46. Disk Usage Alert

47. Memory Usage Report

48. Backup a Directory

49. Delete Old Log Files

50. Complete Beginner System Health Check

Important Bash Test Operators

File Test Operators

Numeric Comparison Operators

String Comparison Operators

Important Special Variables

Important Loop Control Commands

Basic Script Template for Beginners

Common Beginner Mistakes

1. Missing Spaces Around [ and ]

2. Not Quoting Variables

3. Using $10 Instead of ${10}

4. Checking $? Too Late

5. Running Destructive Commands Without Validation

Practice Tasks

Leave a Reply Cancel reply

3. Display All Arguments Using `$@`

4. Difference Between `$*` and `$@`

6. Check the Exit Status Using `$?`

10. Use `shift` to Process Parameters

Part 3 — `for` Loops

21. Basic `for` Loop

23. C-Style `for` Loop

Part 4 — `while` and `until` Loops

31. Basic `while` Loop

32. Countdown Using `while`

33. Read User Input Until `exit`

Part 5 — `case` and Keyboard Menus

39. Basic `case` Statement

40. Service Management with `case`

41. Check Operating System Using `case`

42. Simple Keyboard Menu Using `select`

1. Missing Spaces Around `[` and `]`

3. Using `$10` Instead of `${10}`

4. Checking `$?` Too Late