safecat is an implementation of D. J. Bernstein's maildir algorithm.
It can be used to write mail messages to a qmail-style maildir, or
to write data to a "spool" directory reliably. There are no lockfiles
with safecat, and nothing is left to chance. If safecat returns a
successful exit status, then you can be (practically) 100% sure
your data is safely committed to disk. Further, if data is written
to a directory using safecat (or other implementations of the
maildir algorithm), then every file in that directory is guaranteed
to be complete. If safecat fails to write all of the data, there
will be no file at all in the destination directory.