Checking sudo in Bash (script with if statements)

Question

I've been working with bash for not more than 6 hours, and now I'm trying to create a menu that allows you to do some "fun" stuff:D.

My problem is with the if statement that check if you're in sudo mode. I want to have 3 conditions:

1. If I execute the script with sudo mode, I'll be able to enter the path of the folder to be copied.
2. If I execute the script without sudo mode, it'll ask me to insert the password, if I do that correctly the script will show me the echo and read op that allows me to write the path of the folder to be copied.
3. The same as the point 2, but if I fail the authentication the application will be closed automatically.

Create a copy

2)
    if [ "$EUID" -ne 1 ]
      then 
            echo "Checking if you are in sudo mode..."
            echo "Error, please insert your password:"
            sudo ls /root
            if [ "$EUID" -ne 1 ]
                then
                    echo -e "\nCould not authenticate the user."
                    echo -e "For security reasons the application will be closed."
                    exit    
            else
                echo "==============================================================="
                echo -e "ALL COPIES HAVE A DEFAULT ROUTE: /home/patryk/Desktop/a/"
                echo "==============================================================="
                echo -e "Enter the path of the folder to be copied: "
                read origin
                rsync -avzh $origin /home/patryk/Desktop/a/`date-I`
            fi
    else
        echo "==============================================================="
        echo -e "ALL COPIES HAVE A DEFAULT ROUTE: /home/patryk/Desktop/a/"
        echo "==============================================================="
        echo -e "Enter the path of the folder to be copied: "
        read origin
        rsync -avzh $origin /home/patryk/Desktop/a/`date -I`    
    fi;;    

Answer 1

If you have sudo credentials caching enabled (that is, after a successful sudo, you don't have to enter the password again for subsequent sudos) you could use the following trick:

Execute sudo true and check the return status. If the correct password was entered, the exit code will always be 0 . Otherwise the exit code will be different.

if [[ "$EUID" = 0 ]]; then
    echo "(1) already root"
else
    sudo -k # make sure to ask for password on next sudo
    if sudo true; then
        echo "(2) correct password"
    else
        echo "(3) wrong password"
        exit 1
    fi
fi
# Do your sudo stuff here. Password will not be asked again due to caching.

^{At least on my system, root has the UID 0, not 1, so I adapted the if.}

Answer 2

I think what you really want to do is to check whether your script runs as root or not. If security considerations are not super duper important you could just throw this at the beginning of your script:

if [ "$USER" != "root" ]
then
    echo "Please run this as root or with sudo"
    exit 2
fi

This will work and also cover the case where sudo is used to run command as another user (who is not root)