Summary of Differences between Vi and Xvi

Chris Downey
John Downey

Xvi (pronounced ecks-vee-eye) is a free, portable, multi-window implementation of the popular UNIX editor vi.
This document summarises the differences between the “real” vi and xvi. These differences are divided into three groups: unimplemented features, differences and enhancements, and each of these is described in the following sections.

1. Unimplemented Features

1.1. Ex Mode

The main area in which xvi is lacking is vi's ex mode, which is not implemented at all (and neither are edit, e, and open modes). However, many of the ex commands are available in xvi as colon commands; the colon commands that have not been implemented are mostly those which offer the same functionality as other commands in vi mode.

Specifically, the following ex commands are not implemented, and probably never will be within xvi:

insert undo ex
change open |
append z

while these ex commands, although not currently implemented, may be added as colon commands at some time in the future:

abbreviate recover write>>
unabbreviate join

1.2. Vi commands

The following vi mode commands are not implemented, although there is no real reason why they shouldn't be:

U =

while this one is inappropriate in the context of xvi, since there is no ex mode:

1.3. Parameters

The following parameters have not been implemented, and probably won't be:

ada lisp redraw
adapath mesg slowopen
autoprint modeline term
beautify open terse
directory optimize ttytype
edcompatible prompt window
hardtabs

while these parameters may well be implemented at some point:

ada lisp redraw
autowrite scroll warn
errorbells sourceany writeany

1.4. Miscellaneous

Some features of certain commands do not work as they should. Specifically:

Repeat counts before insertions don't work.
Appending to named buffers is not yet implemented.
Typing ^Q in input mode does not mean the same as ^V; it just inserts a ‘^Q’, assuming it gets as far as the editor at all.
Typing ^W in insert mode does not back up one word as in vi.
It is not possible to interrupt the editor while it is performing certain operations. If you start off a big global command, you have to wait for it to finish.
Flags and counts after colon commands are not supported.
It is not possible to read the output of a system command using
:r !command
or to write into a command using
:w !command
The :substitute command does not support splitting of lines.
Regular expressions, although implemented (see later for more details), do not support the ~ character; also, the \u and \l escape sequences are not supported on the right-hand side of a substitute replacement pattern.
The :global command only supports the commands [lps&~d].
Undo does not work properly when applied to macros (either @ or :map); it should undo all the changes made by the macro, but in fact only the last command within the macro is undone.

2. Enhancements

The following extensions are available in xvi.

2.1. Parameter Handling

Xvi supports 5 types of parameter: as well as vi's numeric, string and boolean, it also has enumerated and list types. The former is used for e.g. format and regextype, while the latter is currently only used for tags. The advantage of the enumerated type is that if you try to set an illegal value, the set of correct values will be displayed, which is very useful if you have forgotten what the values may be. (Try :set preserve to see an example of this.)

2.2. Windows

Xvi supports multiple buffers and windows. A buffer is the object which holds a file in memory, while a window is an area of the screen which shows part of a buffer. Note that every window references a buffer, even if no file is being edited.

The following commands are available for operating on buffers and windows:

:buffer: create a new buffer in a new window; can be followed by a filename, which will be edited in the new buffer.
:split: create a new window onto the current buffer by splitting the current window in half. The two resulting windows are similar to .I viewports on to a single editing buffer, in that changes made in one window are reflected in the other one.
:close: close the current window; will also close the buffer if this is the last window onto it.
:x / ZZ: close only the current window. If the window is the only one onto the buffer, the buffer will be closed as well, writing it first if it is modified. Hence, for a single window, this command does the same as in vi.
g: move to the next window. This is normally the window directly below the current one on the screen, or the top window on the screen if the current window is the bottom one.
^W: increase the size of the current window (may be given a numeric prefix, default is one line).
^T: decrease the size of the current window (may be given a numeric prefix, default is one line).
^O: make the current window as large as possible.
^]: as for vi, but creates a new buffer window if appropriate (and if autosplit allows).

Note that the :quit command quits out of the editor, not out of a window. The :close command is thus the equivalent of :quit for windows. There is no equivalent of :x or ZZ for the whole editor; these have been hijacked for operations on windows.

Also the numeric autosplit parameter specifies the maximum number of buffer windows that will be created automatically whenever you either edit more than one file, or use tags to edit a different file.

Undo works per buffer, as do marks; yank/put and redo (the . command) work over all buffers, i.e. you can delete from one buffer and put the text into a different buffer.

The minrows parameter specifies the minimum number of rows to which a window may be shrunk, including the status line. The default value is 2; 0 and 1 may also be useful.

2.3. Named Buffers

As well as the normal named (conjugate) buffers, and the default one named @, several extra buffers named :, /, ? and ! contain the last command lines entered for each of the command types. So for instance, @: will re-execute the last colon command, or you can insert it into your buffer, edit it and then re-execute it (e.g. with dd@@).

2.4. File Formats

Xvi will handle different file formats, via the format parameter, which may be set to e.g. “unix”, “msdos”, etc. This means you can edit MS-DOS files under UNIX, etc.

2.5. Regular Expressions

Vi's magic parameter is replaced by the regextype parameter, which can take the following values:

tags: only ^ and $ are significant (used for tags).
grep: like grep(1), but with \< and \> added.
egrep: like egrep(1), but with \< and \> added.

The default is grep.

The sections and paragraphs parameters define egrep-style patterns to search for, rather than vi's simplistic (and troff-dependent) character pairs.

The sentences parameter is also implemented in this fashion, but this is not completely satisfactory at the moment.

Note that it is possible to set or unset the magic parameter as in vi; this will simply result in the regextype parameter being set as appropriate.

2.6. Colour

Xvi has a minimal amount of support for colours. Basically, there are considered to be four settable colours, each with a numeric parameter to say what its value is:

colour: colour used for text
statuscolour: colour used for status lines
roscolour: as statuscolour, but for readonly files
systemcolour: colour used for system mode (i.e. subshells and after termination).

The actual values of these parameters are system-dependent; on PC versions, they are hardware-dependent video attributes, while on UNIX they are indexes into the entries “c0” to “c9” in the termcap(5) database, which are assumed to be colour-setting escape sequences if they are present. If they are not present, “so” (begin standout mode) and “se” (end standout mode) are used instead. Values of 0 and 1 give normal text, 2 to 9 give standout mode.

The default colour for the roscolour parameter will usually involve red if colours are available; this is intended to provide a warning to the user that writing the file may not be possible.

The colour values may be entered in decimal, octal or hexadecimal form. This may be convenient for PC versions where the numbers actually represent colour bitmaps; for example, on MS-DOS,

:set co=0x1f

gives bright white text on a blue background.

2.7. Replace Mode

Xvi's replace mode (entered by the R command) acts more intelligently when you press the return key -- it leaves the rest of the current line alone, and just starts replacing text on the next line, starting at the screen column where you first typed R.

2.8. Preserve

Rather than use vi's UNIX-specific method for preservation, xvi does periodic preservation of all files currently being edited into a temporary file in the same directory. Xvi tries to do this when you are not typing, so that you won't notice the short delay when the temporary file is written out. Obviously, only changed files are preserved in this way, and the temporary file is normally removed once the real file has been successfully written. As an additional safety measure, when a file is explicitly saved and it appears not to have been preserved recently, it is normally preserved first. This ensures that, even if the operating system crashes while the real file is being created, there should always be at least one recent copy of it in the filesystem. The :preserve command is available as in vi to preserve a specific buffer manually.

The level of safety provided by the preservation facility may be configured by changing the values of the preserve and preservetime parameters. The following values are available for preserve:

unsafe: Never preserve any buffer before an explicit save. This can be useful on old, slow, floppy-only systems, but is not generally recommended.
standard The: default value. Only preserve a buffer before an explicit save if it appears not to have been preserved recently.
safe: Always preserve buffers before they are written.
paranoid: As for safe, but the preserve file is never removed, even after the file has been successfully written.

In all cases, all modified buffers are preserved automatically after no user events have been received for preservetime seconds, if a minimum number of events (currently 60) have been received since the last automatic preservation. This behaviour can be more or less disabled by setting preservetime to a very high value. (For example, one of the authors sets it to 600 on the machine he uses at home, which is an 8088-based PC with no hard disk; by way of contrast, on the SparcStation IPX which he uses at work, he sets it to 2.)

The names given to preserve files are system-dependent, but are generally of the form “filename.tmp”, or “filename.001” to “filename.999”. If a preserve file already exists, it will not be overwritten; instead, a new filename will be generated.

The -r command line option is not supported.

2.9. Help

A primitive help facility is available; the command :help, also mapped to the HELP or F1 keys on many systems, simply creates a new buffer window onto a standard help file. The name of the file which is edited is given by the helpfile string parameter; the default on Unix versions is "/usr/lib/xvi.help".

2.10. Scrolling

The jumpscroll enumerated parameter controls the editor's behaviour when the cursor moves beyond the limits of the current window. If its value is off, and the new position is still reasonably close to the current window, the window will be scrolled so that the new cursor position is at the top or bottom of it. Typically, the window will be scrolled one line at a time as the cursor is moved up or down. This behaviour may not always be desirable; for example, terminals without real scrolling regions may force the editor to do a lot of screen updating, possibly over a slow telephone line or overloaded network. Also, on LCD screens or other displays with a long image persistence, it may make the text more difficult to read. If jumpscroll is set to on, scrolling behaviour is modified so that, whenever the cursor moves beyond the limits of the current window, the window is redrawn so as to place the cursor as centrally as possible in it; thus, the window appears to jump to the new position. The default value for jumpscroll is auto, which causes the editor to jump instead of scrolling only if it can't scroll the affected window efficiently.

In all cases, if the distance from the top or bottom of the window to the new position is more than half the window size, the editor will jump instead of scrolling.

Explicit scroll commands (e.g. ^D) are not affected by the jumpscroll parameter.

2.11. 8-bit Characters

Characters with the top bit set may be displayed, although it is not yet possible to have null ('\0') bytes in a file buffer. How the characters are displayed varies between systems; on UNIX, they will be shown as an octal escape sequence, while on MS-DOS, OS/2 and QNX they will be shown as the actual character in the PC character set. This can be controlled by setting the cchars and mchars variables; if these parameters are set, control- and meta-characters (respectively) are shown directly, otherwise they are shown as some sequence of printable characters.

You can use the ^_ (control-underscore) command to flip the top bit of the character the cursor is on. This may be useful on systems where it is otherwise impossible to enter 8-bit characters.

Tabs are normally displayed as a series of spaces of the appropriate length (according to the tabstops parameter); setting list mode will cause them to be displayed as a control character, as will unsetting the tabs parameter. How the tab character is displayed is then under the control of the cchars parameter.

2.12. Mouse Support

Some mouse support is available for micro-based systems and workstations. Clicking the mouse button on:

any line outside current window: changes current window to the one indicated by the mouse (can be used instead of g).
top line of any window: scrolls window downwards (same as ^Y).
bottom line of any window: scrolls window upwards (same as ^E).
status line of any window: shows current file and lines (same as ^G).
any text line of any window: moves text cursor as near as possible to mouse cursor.

Also, windows can be resized by “dragging” the appropriate status line up or down with the mouse.

2.13. Miscellaneous

The :wn (write file and edit next) command is provided, as per PC-vi.
There is no limit to the number or size of maps which may be defined, nor is there any fixed limit to the number of lines in a buffer.
The edit parameter controls whether a buffer can be modified. This may be used, together with the readonly parameter, to implement a nicer version of view(1) than vi's version, since it won't fool you into thinking that editing the buffer is in any way safe. Be warned: once having set noedit, it is not possible to do a :set edit. It's a one-way street.
The timeout parameter is implemented as a numeric value, specifying the number of milliseconds after which to assume that no further input is available to continue with the parsing of a map sequence. This replaces vi's boolean parameter of the same name.
The vbell parameter may be used to specify use of a visual, rather than audible, bell, if this is available.
The :echo command is available; it simply echoes its arguments, after expansion of % and # characters.
In insert and replace modes, ^A has the same meaning as ^@ in vi, except that it works at any time, not just for the first character. Also, typing ^Bx, where x is the name of a conjugate buffer, inserts the contents of that buffer into the input stream at that point. The buffer named < always contains the last thing inserted, so that ^B< is the same as ^A.

3. Differences

Argument handling is somewhat different; for instance, -R is not supported, but “-s parameter=value” is, which is much more useful anyway.
The XVINIT environment variable is read instead of EXINIT. Whilst no files are sourced automatically, users who wish to have a startup file can arrange it very easily. sh(1) or ksh(1) users should add this line to their "$HOME/.profile":
XVINIT='source xvi-startup-file'; export XVINIT
csh(1) users should add this to their "$HOME/.login":
setenv XVINIT 'source xvi-startup-file'
and MS-DOS users should add this to their autoexec.bat:
set XVINIT=source xvi-startup-file
The tags parameter can be used to specify multiple tags files; these can be separated by either “\ ” (backslash space) or “,” (comma).
Alternate files are handled slightly differently, owing to the presence of buffer and window handling. Essentially, when you close a buffer, its filename is remembered as the alternate file; when you invoke the ^^ or :e # commands, this filename is re-edited. Note that ^^ edits the alternate file in a new buffer window.
Hitting the escape key while in the command line does not terminate input; instead, it cancels input, returning the prompt to the beginning of the line. This applies to input for :, /, ? and !.
Character-based yanks (or deletes) which span line boundaries are handled correctly (vi gets this wrong).

HTMLed by martinwguy@users.sourceforge.net, 23 Nov 2005 from the version distributed with xvi 2.47.
Please report any errors or remaining troff markup.

abbreviate	recover	write>>
unabbreviate	join

ada	lisp	redraw
adapath	mesg	slowopen
autoprint	modeline	term
beautify	open	terse
directory	optimize	ttytype
edcompatible	prompt	window
hardtabs