Challenge_10

1. Create a Bash script named script1.sh. Add the shebang.
   Define a variable called country that holds the country you are living in.
   Print the message: You live in YOUR_COUNTRY.
Sol.
#!/bin/bash
country="Romania"
echo "I live in $country."


2. Create a script and define two string variables.
   Add a commented line after the shebang and another inline comment.
   Create a new variable by concatenating the two string variables.
Sol.
#!/bin/bash 
# This is a very simple Bash script.
var1="Ubuntu " 
var2="20.04" 
var3="$var1$var2" # concatenating 2 strings
echo $var3


3. Develop a Bash script that creates a new group and a new username. The group will be the user’s secondary group.
   The username and the group will be given as input by the user that runs the script.
   The script will also display the last 2 lines from the files where the users and the groups are saved in Linux.
Sol.
#!/bin/bash
read -p "Enter the group name to create: " group
read -p "Enter the username to create: " username
groupadd $group
useradd -s /bin/bash -m -G $group $username
tail -n 2 /etc/group
echo 
tail -n 2 /etc/passwd
echo
echo "The group $group and the username $username were created!"


4. Create a script called fix_permissions.sh that prompts the user for a directory and changes the permissions of all subdirectories to 755 and to all files to 644 recursively.
Sol.
#!/bin/bash
read -p "Enter directory: " dir
echo -n "Changing files permissions to 644 recursively..."
find $dir -type f -exec chmod 644 {} \;
echo "Done"
echo -n "Changing subdirectories permissions to 755 recursively..."
find $dir -type d -exec chmod 755 {} \;
echo "Done"


5. Create a script that takes an argument and tests if it's a file or not.
Sol.
#!/bin/bash
if [[ -f "$1" ]]
then	
	echo "The argument is a regular file."
else
	echo "The argument is not a regular file."
fi


6. Consider the solution from the previous challenge. Change it so that it tests if the script is run with exactly one argument.
Sol.
#!/bin/bash
if [[ $# -eq 1 ]]
then
	if [[ -f "$1" ]]
	then	
		echo "The argument is a regular file."
	else
		echo "The argument is not a regular file."
	fi
else
	echo "The script was run with $# arguments. You should run it with exactly one argument."
fi


7. Create a script that clears the contents of a text file which is the script’s argument.
   Test that the argument is a file.
Sol.
#!/bin/bash
if [[ -f $1 ]]
then
	echo "" > $1 
    # cat /dev/null > $1
	echo "$1 contents was cleared!"
else
	echo "The script's argument should be a file!"
fi


8. Develop a script that appends to a file the currently logged in users and the current date and time.
Sol.
#!/bin/bash
users="`who | cut -f1 -d" "`"
date_time="`date +%F\ %H:%M`"   #\ to escape the whitespace
echo $date_time >> logged_users.txt
echo "-------------------------" >> logged_users.txt
echo $users >> logged_users.txt
echo >> logged_users.txt 


9. Create a script that takes exactly two arguments. The first argument is a shell command and the second argument is a string. The script will check if the string belongs to the 
   output of the command.
Sol.
#!/bin/bash
if [[ $# -ne 2 ]]
then
	echo "Run the script with exactly two arguments."
	exit
else
	output="`$1`"
	if [[ "$output" == *"$2"* ]]
	then
		echo "$2 belongs to the output of $1"
	else
		echo "$2 DOES NOT belongs to the output of $1"
	fi
fi


10. Create a script that prompts the user for a file. Test that it’s a file.
    Prompt the user for 2 positive integers n and m.
    Display the lines (from line number n to m, both inclusive) of the text file.
Sol.
#!/bin/bash
read -p "Enter a file: " file

if [[ -f $file ]]
then
		read -p "Enter a positive integer n: " n
		read -p "Enter a positive integer m: " m
		q=$((m-n+1)) # no. of lines to display

		tail -n "+$n" $file | head -n $q
else
	echo "$file is not a file."
fi


11. Develop a script that prompts the user for a number n. 
    Add a testing condition so that the user enters a positive integer less than 100
    and then it creates a file every 3 seconds and the name of each file will be current_minute_second
Sol.
#!/bin/bash
read -p "Enter the number of files to create:" n
if [[ $n -le 0 ]] || [[ $n -ge 100 ]] 	# || is the logical OR operator
then
	echo "You entered $n. Enter a positive integer less than 100."
	exit 
fi
i=0
while [[ $i -lt $n ]]
do
	minute_second="$(date +%M%S)"
	echo "Creating $minute_second"
	touch "$minute_second"
	((i++))
	sleep 3
done
echo "$n files were created!"


12. Create a script that takes 3 arguments: a file extension, a source directory and a destination directory given as absolute or relative paths to the script. 
    The script will copy all the files with that extension from the source directory to the destination directory.
Sol.
#!/bin/bash
# $1 - file extention (without .)
# $2 - source directory
# $3 - destination directory
for file in $2/*.$1
do
	echo "Copying $file to $3"
	sleep 1
	cp $file $3
done


13. Create a Bash Menu with the following entries:
    Display Date and Time
    List users logged in
    Display disk usage
    Change the Menu Prompt to the string Choose:
Sol.
#!/bin/bash
PS3="Choose:"
select MENUITEM in "Display Date and Time" "List users logged in" "Display disk usage" "Quit"
do
	case $REPLY in
		1)
			date
			;;
		2)
			who -aH
			;;
		3)
			df -h
			;;
		4)

			echo "Quitting ..."
			sleep 1
			exit
			;;
		*)
			echo "Unknown selection."
			;;
	esac
done