On Sat, 6 Jul 1996, VaX#n8 wrote:

> Has anyone written  a script like this that invokes the install
> program only if the source contents != the target contents.
> 
> Does anyone think this would/wouldn't be a good patch to the install program?
> 
> I think this is a fairly common idiom and useful in both build environments,
> as well as mtree/tripwire-style systems (the two environs I can think of
> that really use mtimes).
> 
> I've written (well, stolen) "cp-if-change" and "mv-if-change" from some
> GNU tools.  Trivial scripts, really, but they don't have the full
> capabilities of their /bin counterparts (can't cp multiple files into
> a dir, etc).
> 

FreeBSD has implemented this as install -C (capital C) which copies the 
new file only if it is different from the existing one.