Unpack reads from a string, not a filehandle. You need to read from the file first. This works for me:

my $file = $ARGV[0];
open my $fh, '<', $file or die "open: $file: $!\n";
binmode $fh, ':raw';

my $buf;
my $n = read($fh, $buf, 2);
die "got $n bytes\n" unless $n == 2;

my @values = unpack 'S<', $buf;
printf "0x%x\n", $_ for @values;
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Dave.