diffutils: patch and POSIX
10.12 'patch' and the POSIX Standard
====================================
If you specify the '--posix' option, or set the 'POSIXLY_CORRECT'
environment variable, 'patch' conforms more strictly to the POSIX
standard, as follows:
* Take the first existing file from the list (old, new, index) when
intuiting file names from diff headers. ⇒Multiple Patches.
* Do not remove files that are removed by a diff. ⇒Creating and
Removing.
* Do not ask whether to get files from RCS, ClearCase, or SCCS. ⇒
Revision Control.
* Require that all options precede the files in the command line.
* Do not backup files, even when there is a mismatch. ⇒
Backups.