Hello all! I am very new to shell and Linux in general (I just started 2 days ago), I am trying to write a script that adds the size of the directories and files in a given directory and displays messages if the user puts in something wrong. I think I have covered all the possible problems except for one, I don't know how to make sure that the script checks that the user inputs only one directory and not more? If I try to run this program with 2 or more directories, then it runs the script for the first directory. How can I make the script to output a message saying that the user should specify only one directory to run the script on and not more?

Code:

#!/bin/sh
DIR="$1"
if [ $# -lt 1 ]
then
        echo "You haven't given any parameters, please give a directory and run the program in the following format: sh <programname.sh> <directory>"

elif [ ! -e "$DIR" ]
then
        echo "The directory you have specified does not exist."

elif [ ! -d $DIR ]
then
        echo "The parameter you have specified is not a directory, please specify a directory to run the program."
else
        du -s -m "$DIR"
fi

Thank you in advance for your help!