Illustrative example:

use strict;
use warnings;

use Ref::Util 'is_hashref';
use Test::More tests => 2;

my %hash;

$hash{foo} = 1;
$hash{bar} = { baz => 'quux' };

ok is_hashref ($hash{bar});
ok not is_hashref ($hash{foo});
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See perlreftut and perldsc.