bksh is a simple (some would say trivial) program designed to be used
as a shell by ssh or rsh-like programs. All it does it to copy its
input to a restricted set of backup files.

It was made to allow administrators to create backup servers in
potentially hostile environments without allowing full shell access to
the server or the client.

Features:
- tape only or file & tape backups (compile-time config)
- automatic file rotation allows keeping a history of backups
- configurable number of files kept (static compile-time or dynamic)
- allows naming of backup files on command line
- works as a restricted shell to limit access to server
- very simple and short ANSI C code, easy to audit