Develop a Perl script that counts the number of uppercase letters in a file. The script should read in the file as a command line argument and output the total count of uppercase letters found in the file. The script should ignore any non-alphabetic characters (such as numbers and punctuation) and count only uppercase letters from A-Z. The output should be printed to the terminal. The script should be well-commented and easy to read, with clear variable names and error handling.
This prompt doesn't seem malicious.