#!/usr/bin/perl

# This helps you to write better code and save time on debugging
use strict;
use warnings;

# Pass the command line argument(s) to the function
getFileName(@ARGV);

sub getFileName {
    # The argument list @ARGV is an array, read the first element if exists
    my $fileName = defined($_[0]) ? $_[0] : '';

    # Prompt for user input until the file exists
    while (! -e $fileName) {
        print "Please enter a filename that exists. ";
        $fileName = <STDIN>;
        chomp($fileName); #Remove the newline char at the end of input
    }

    return $fileName;
}