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. See section Multiple Patches in a File.
• Do not remove files that are removed by a diff. See section Creating and Removing Files.
• Do not ask whether to get files from RCS, ClearCase, or SCCS. See section Revision Control.
• Require that all options precede the files in the command line.
• Do not backup files, even when there is a mismatch. See section Backup Files.