if (open my $fo, '<', $ggg) {
    # Process the file.
} else {
   # Your code to exit.
}

##</code><code>##

{
    print "'$ggg' is missing:\nEnsure that this file is in the working dir.\nWe are exiting.\n";
    my $answer;
    while ('q' ne lc $answer) {
        print "Please press 'q' and Enter to quit\n";
        chomp($answer = <STDIN>);
    }
    exit;
}