my $file = "somefile.utf8";

# create a UTF-8 encoded test file, explicitly adding a BOM
open my $out, ">:utf8", $file or die $!;
print $out "\x{feff}foo bär";
close $out;

# read it back in
open my $in, "<:encoding(utf8)", $file or die $!;
$_ = <$in>;
use Devel::Peek;
Dump $_;