Question

I’m using Perl’s Getopt::Long module to parse command line arguments. However, it seems that it returns a true value even if some of the arguments are missing. Is there a way to tell if this is the case?

Answer 1

In plain old Getopt::Long, you can’t do this directly — as Jonathan said, you need to check your requirements for undef. However, IMHO this is a good thing — what is a “required” parameter? Often one has parameters that are required in one case and not another — the most common example here being the sore thumb of the --help option. It’s not required, and if the user uses it, he probably doesn’t know to or won’t pass any of the other “required” parameters.

I use this idiom in some of my code (well, I used to, until I switched to using MooseX::Getopt):

use List:MoreUtils 'all';

Getopt::Long::GetOptions(\%options, @opt_spec);
print usage(), exit if $options{help};
die usage() unless all { defined $options{$_} } @required_options;

Even with MooseX::Getopt I don’t set my attributes to required => 1, again because of the --help option. Instead I check for the presence of all attributes I need before moving into the main body of program execution.

package MyApp::Prog;
use Moose;
with 'MooseX::Getopt';

has foo => (
    is => 'ro', isa => 'Str',
    documentation => 'Provides the foo for the frobnitz',
);
has bar => (
    is => 'ro', isa => 'Int',
    documentation => 'Quantity of bar furbles to use when creating the frobnitz',
);

# run just after startup; use to verify system, initialize DB etc.
sub setup
{
    my $this = shift;

    die "Required option foo!\n" unless $this->foo;
    die "Required option bar!\n" unless $this->bar;

    # ...
}