If a nonexistent input file is under a revision control system
patch normally asks the user
whether to get (or check out) the file from the revision control
system. Patch currently supports RCS, ClearCase and
SCCS. Under RCS and SCCS,
patch also asks when the input file is read-only and matches
the default version in the revision control system.
The --get=num (-g num) option affects access
to files under supported revision control systems. If num is
patch gets the file without asking the user; if
patch neither asks the user nor gets the file; and if
patch asks the user before getting the file. The
default value of num is given by the value of the
PATCH_GET environment variable if it is set; if not, the default
value is zero if
patch is conforming to POSIX, negative
patch and the POSIX Standard.
The choice of revision control system is unaffected by the
VERSION_CONTROL environment variable (see Backup File Names).