in reply to OpenBSD's patch
I'd try searching for the string "--dry-run" in the output of "patch --help".
Both "--help" and "--dry-run" are probably GNU specific (GNU uses double dashes). On other systems, "patch --help" will give you error messages, but will never print "--dry-run".
By the way, according to the man page, OpenBSD's patch program is derived from the one authored by Larry Wall.
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