This specifies whether patch gets missing or read-only files from RCS, ClearCase, Perforce, or SCCS by default; see the -g or --get option.
If set, patch conforms more strictly to the POSIX standard by default: see the --posix option.
Default value of the --quoting-style option.
Extension to use for simple backup file names instead of .orig.
Directory to put temporary files in; patch uses the first environment variable in this list that is set. If none are set, the default is system-dependent; it is normally /tmp on Unix hosts.
Selects version control style; see the -v or --version-control option.

$TMPDIR/p*
temporary files
/dev/tty
controlling terminal; used to get answers to questions asked of the user

diff(1), ed(1), merge(1).

Marshall T. Rose and Einar A. Stefferud, Proposed Standard for Message Encapsulation, Internet RFC 934 <https://datatracker.ietf.org/doc/html/rfc934> (1985-01).