You can check that with the ref function:

use strict;
my $var = [qw(this is an array)];
print ref $var;

my $var = "This is a scalar";
print ref $var;

my $var = { message => "This is a scalar" };
print ref $var;
[download]

But you really, really want to use the ForceArray configuration parameter to make all your results arrays, whether there is one or more elements in the XML.

Wow, that's probably the fastest I've ever recieved help! Thanks alot, its solved my problem.

That's a feature of XML::Simple - this difference of behavior between a node which happens once or multiple times. Most of the time, when you expect a node that happen one or more times, you want to tell XML::Simple to always return an array of hashes, so you have a uniform way to deal with the data.

That's what ForceArray attribute for.

$data = XMLin( $xml, ForceArray => [ qw(Layer) ] )
[download]

Otherwise you'll always have to code something like that:

my $layers = $data->{Capabilities}->{Layer};
for my $layer ( ref $layers eq 'ARRAY' ? @$layers : ( $layers ) ) {
    # do something to each Layer
}
[download]

You could do soemthing simple like (ref $var) eq "ARRAY" or something as complicated as Scalar::Util::reftype( $var ) eq "ARRAY". The later is usually only necessary if you're working with blessed scalars.

I'd be surprised if there wasn't some XML::Simple built-in way to determine how to branch though.