tempfile, UNLINK, and flock

gistfile1.txt

my $fn = do {
    # some BSD variants (notably OS X) flocks the file handle when calling tempfile()
    my ($fh, $fn) = tempfile(UNLINK => 1);  
    $fn
    # setting UNLINK => 1 keeps a hidden reference to the file handle, and thus the file
    # is not automatically closed when exitting this block
};

open my $fh, "<", $fn
    or die $!;
# flock blocks forever since the file is already locked
flock($fh, LOCK_EX)
    or die $!'