Recognize unknown options in Getopt::Long

Question

How can you recognize unknown options using Getopt::Long?

I tried <>, but it did not work as expected. Consider:

use Modern::Perl;
use Getopt::Long;

my $help='';
GetOptions ('help' => \$help,'<>' => \&usage);
usage() if $help;

usage() if @ARGV != 1;

my $fn=pop;

say "FileName: $fn";

sub usage {
    say "Unknown option: @_" if ( @_ );
    say "Usage: $0 <filename>";
    say "       $0 --help";
    say "";
    exit
}

I would like to print Unknown option only if there is an unrecognized option (in this case, anything other than --help). But, now it thinks the filename is an unrecognized option.

Answer 1

Call your usage function if GetOptions fails. Getopt::Long will print Unknown option for you (to STDERR):

use Modern::Perl;
use Getopt::Long;

my $help='';
GetOptions ('help' => \$help) or usage();
usage() if $help;

usage() if @ARGV != 1;

my $fn=pop;

say "FileName: $fn";

sub usage {
    say "Usage: $0 <filename>";
    say "       $0 --help";
    say "";
    exit
}