if [ $# -eq 0 ] then echo "No arguments supplied" fi
The $# variable will tell you the number of input arguments the script was passed.
Or you can check if an argument is an empty string or not like:
Check if arg is filled in
if [ -z "$1" ] then echo "No argument supplied" fi
The -z switch will test if the expansion of "$1" is a null string or not. If it is a null string then the body is executed.