If a nonexistent input file is under a revision control system supported by patch, 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 positive, patch gets the file without asking the user; if zero, patch neither asks the user nor gets the file; and if negative, 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 otherwise. See patch and POSIX.
The choice of revision control system is unaffected by the VERSION_CONTROL environment variable (see Backup Names).