How do I re-build my system without clobbering the existing installed binaries?

Frequently Asked Questions for FreeBSD 2.X : Miscellaneous Questions : How do I re-build my system without clobbering the existing installed binaries?
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7.11. How do I re-build my system without clobbering the existing installed binaries?

If you define the environment variable DESTDIR while running ``make world'' or ``make install'', the newly-created binaries will be deposited in a directory tree identical to the installed one, rooted at ${DESTDIR}. Some random combination of shared libraries modifications and program rebuilds can cause this to fail in ``make world'', however.