From: shane@mit-ajax (K. Shane Hartman)
I have created a mechanism for automatically updating your Gnu Emacs
sources from the sources maintained on mit-prep. To take advantage of this
mechanism you must have a connection to the internet and do the following:

Obtain the modified version of rcp from mit-prep. This version is upward
compatible with standard rcp. The relevant files are:
mit-prep:/u2/emacs/rcp.binary (compiled for vax 4.2)
mit-prep:/u2/emacs/rcp.1c
mit-prep:/u2/emacs/RCP.README
You can use ftp to obtain the files or rcp (the old version will work for
this, just do 'rcp mit-prep.rcp:/u2/emacs/rcp.binary rcp.binary' ...

If you have a source license, /u2/emacs/rcp.diff may be useful: it is
a diff of ucb rcp and the modified rcp.

Replace your current copy of rcp with rcp.binary (it must suid to root),
but keep the old copy around just in case (e.g. rename to rcp.ucb) and
install the man page.

Now connect to your toplevel emacs directory (which contains src, etc, dbx,
lisp, and info) and do:

rcp -ruvp "mit-prep.rcp:/u2/emacs/dist/*" .

The new options: v - verbose, u - update, and p - preserve write dates.
The rcp 'account' supports only the rcp command.

Once you have synchronized with the write dates for the files on prep, the
above command is sufficient to update all and only those files that have
changed on prep with respect to your sources. For this scheme to work, you
must maintain the sources on your own machine and be aware that if you
change a source on your machine, then rcp can be fooled.