This utility shall be provided on systems that both support the
User Portability Utilities option and define the POSIX2_CHAR_TERM
symbol. On other systems it is optional.
The vi (visual) utility is a screen-oriented text editor. Only
the open and visual modes of the editor are described in
POSIX.1‐2008; see the line editor ex for additional editing
capabilities used in vi. The user can switch back and forth
between vi and ex and execute ex commands from within vi.
This reference page uses the term edit buffer to describe the
current working text. No specific implementation is implied by
this term. All editing changes are performed on the edit buffer,
and no changes to it shall affect any file until an editor
command writes the file.
When using vi, the terminal screen acts as a window into the
editing buffer. Changes made to the editing buffer shall be
reflected in the screen display; the position of the cursor on
the screen shall indicate the position within the editing buffer.
Certain terminals do not have all the capabilities necessary to
support the complete vi definition. When these commands cannot be
supported on such terminals, this condition shall not produce an
error message such as ``not an editor command'' or report a
syntax error. The implementation may either accept the commands
and produce results on the screen that are the result of an
unsuccessful attempt to meet the requirements of this volume of
POSIX.1‐2017 or report an error describing the terminal-related
deficiency.
