This post assumes that you have read the bash script beginner guideso that you know how to give file permissions and how to execute the bash script.

1. Write a BASH script to create a backup of the current directory that you are working on.

Usage: ./backup.sh

No command line arguments are needed as the script will take a backup of the current directory that you are working on.

#!/bin/bash

echo "Creating a backup of the $(pwd) directory"
tar -cvf ~/bash-scripting/mybackup_"$(date +%d-%m-%Y_%H-%M-%S)".tar $(pwd) 2>/dev/null
echo "Finished backing up $(pwd)"

Output of the above script is as follows:

After executing the script, we can see that a new .tar file was created with current date and time. This is done so that the .tar won't get overwritten each time a backup is created.

2. Write a BASH script that will add two nos, which are supplied as command line arguments, and if this two nos are not given, show error and its correct usage.

#!/bin/bash

# Author: Sebin Sebastian
# Created: 24th March 2022
# Last Modified: 24nd March 2022

# Description:
# Write shell script that will add two nos, which are supplied as command line argument,
# and if this two nos are not given show error and its usage

# Usage
# ./filename num1 num2

if [ -z "$2" ] ; then
        echo "No input arguments."
        echo "usage: $0 <arg1> <arg2>"
        exit 1
else
        echo "The sum of $1 and $2 is: "
        echo $(( ${1:-0} + ${2:-0}))
        exit 0
fi
exit 0

The output of the above script is as follows.

3. Write a BASH script to find out the biggest number from the given three numbers. The numbers should be provided as command line arguments and throw error if not provided.

#!/bin/bash

# Author: Sebin Sebastian
# Created: 24th March 2022
# Last Modified: 24nd March 2022

# Description:
# Write Script to find out biggest number from given three nos.
# Nos are supplied as command line arguments.
# Print error if sufficient arguments are not supplied.

# Usage
# The solution has been explained in the readme file. Refer the readme
# file along with this solution.

if [ $# -ne 3 ]; then
        echo "No arguments supplied"
        echo "usage: $0 <arg1> <arg2> <arg3>"
        exit 1
fi

if [ $1 -eq $2 ] && [ $1 -eq $3 ]; then
        echo "All numbers are equal."

elif [ $1 -gt $2 -a $1 -gt $3 ]; then
        echo "$1 is the largest."

elif [ $2 -gt  $1 -a $2 -gt $3 ]; then
        echo "$2 is the largest."

else
        echo "$3 is the largest."

fi