$ perl -E '
    use lib ".";
    use Pm_11110263_FilenameGen "gen_filename";
    say gen_filename($ARGV[0]);
' 'daily_~DATE DMY~_monthly_~DATE MY~_yearly_~DATE Y~_BAD_~RM ROOT~.log'
FATAL! 'RM ROOT' is invalid at Pm_11110263_FilenameGen.pm line 26.