In a pure BSD environment, nvi is installed
under the names ex, vi,
and view.  Typically they are all links
to the same executable, and nvi looks at how
it is invoked to determine its behavior.
(UNIX vi works this way too.)
It allows the Q command from vi mode
to switch into ex mode.
The view variant is like vi,
except that the readonly option is set initially.
nvi has a number of command-line options. The most useful are described here:
-c commandExecute command upon startup. This is the POSIX
version of the historical +command
syntax, but nvi is not limited to positioning commands.
(The old syntax is also accepted.)
-FDon't copy the entire file when starting to edit. This may be faster, but allows the possibility of someone else changing the file while you're working on it.
-R-rRecover specified files, or if no files are listed on the command line, list all the files that can be recovered.
-SRun with the secure option set, disallowing
access to external programs.[3]
[3] As with anything labelled "secure," blind trust is usually inappropriate. Keith Bostic says, though, that you can trust nvi's
secureoption.
-sEnter batch (script) mode. This is only for ex, and is intended for running editing scripts. Prompts and non-error messages are disabled. This is the POSIX version of the historic "-" argument; nvi supports both.
-t tag-w size