Incidentally, I've bumped up against another issue on HP-UX (really, it's going to be an issue on any Unix that doesn't ship with a /usr/bin/install or equivalent):

Since there's no 'install' available, Ruby falls back to using ./install-sh -c.  This is fine when building Ruby, but it means that rbconfig.rb will set CONFIG["INSTALL"] = "./install-sh -c" when gems and ruby extensions are being built.  Not all gems _have_ an ./install-sh to run...

Workaround:

Put a copy of an install-sh at /usr/local/bin/install or similar.

Ideally, do this before building Ruby.  If you've already built Ruby, modify rbconfig.rb to point to it -- provided you put the install script somewhere on your path, CONFIG["INSTALL"] = "install -c" should be fine.

-mental