smart copy/update routine

[James Christopher Beard]

Is there such a thing available as unix source?  What I need is a
program that can be told to copy files from source to target iff the
file to be copied does not exist on the target or the source version
is newer than the version in the target directory.  (A useful option
would be to change the above "or" to an "and," so that only files
already present at the target would be copied, and only if the source
version were newer.

As an alternative, is there source for the "newer" utility available?
I have seen a man page for it, and it would allow one to write scripts
with the above functionality, but I can't find source or executable.

If I learn anything, I'll summarize for the net.

Thanks for any help.

James Beard
beard at informatics.wustl.edu