$ /usr/bin/perl
use strict;
use warnings;

my $c = 'a';
my $fd;

open $fd, '>:encoding(utf16le)', 'foo-le' or die "open: $!";
print $fd $c;
close $fd;

open $fd, '>:encoding(utf16be)', 'foo-be' or die "open: $!";
print $fd $c;
close $fd;

open $fd, '>:encoding(utf16)', 'foo' or die "open: $!";
print $fd $c;
close $fd;
__END__
$ xxd foo-le
0000000: 6100                                     a.
$ xxd foo-be
0000000: 0061                                     .a
$ xxd foo
0000000: feff 0061                                ...a
$ /usr/bin/perl
open my $fd, '<:encoding(utf16)', 'foo' or die "open: $!";
print while <$fd>;
close $fd;
__END__
a