File::At
========

File::At is a thin FFI::Platypus wrapper around the POSIX "at" family of
filesystem syscalls (openat, fstatat, unlinkat, mkdirat, linkat, etc.).

It exposes:

- constants like AT_FDCWD, AT_SYMLINK_NOFOLLOW, AT_REMOVEDIR, ...
- direct bindings to the underlying libc functions
- a small helper object, File::At::Dir, which owns a directory fd
- convenience helpers open_fd_at() and open_fh_at() for opening files
  relative to a directory fd

Typical usage:

  use File::At qw(dir open_fh_at AT_FDCWD);
  use Fcntl qw(O_RDONLY);

  my $root = dir("/some/base");
  my $fh   = open_fh_at($root, "subdir/file.txt", O_RDONLY, 0);

See eg/at_hardlink.pl for a more complete example: it walks two directory
trees and, when files match by MD5, replaces the destination file with a
hard link to the source using linkat().