Chapter 6. Editing

Table of Contents

6.1. Introducing vi
6.1.1. The vi interface
6.1.2. Switching to Edit Mode
6.1.3. Switching Modes & Saving Buffers to Files
6.1.4. Yanking and Putting
6.1.5. Navigation in the Buffer
6.1.6. Searching a File, the Alternate Navigational Aid
6.1.7. A Sample Session
6.2. Configuring vi
6.2.1. Extensions to .exrc
6.2.2. Documentation
6.3. Using tags with vi

6.1. Introducing vi

It is not like the vi editor needs introducing to seasoned UNIX users. The vi editor, originally developed by Bill Joy of Sun Microsystems, is an endlessly extensible, easy to use light ASCII editor and the bane of the newbie existence. This section will introduce the vi editor to the newbie and perhaps toss in a few ideas for the seasoned user as well.

The first half of this section will overview editing, saving, yanking/putting and navigating a file within a vi session. The second half will be a step by step sample vi session to help get started.

This is intended as a primer for using the vi editor, it is not by any means a thorough guide. It is meant to get the first time user up and using vi with enough skills to make changes to and create files.

6.1.1. The vi interface

Using the vi editor really is not much different than any other terminal based software with one exception, it does not use a tab type (or curses if you will) style interface, although many versions of vi do use curses it does not give the same look and feel of the typical curses based interface. Instead it works in two modes, command and edit. While this may seem strange, it is not much different than windows based editing if you think about it. Take this as an example, if you are using say gedit and you take the mouse, highlight some text, select cut and then paste, the whole time you are using the mouse you are not editing (even though you can). In vi, the same action is done by simply deleting the whole line with dd in command mode, moving to the line you wish to place it below and hitting p in command mode. One could almost say the analogy is mouse mode vs. command mode (although they are not exactly identical, conceptually the idea is similar).

To start up a vi session, one simply begins the way they might with any terminal based software:

$ vi filename

One important note to remember here is that when a file is edited, it is loaded into a memory buffer. The rest of the text will make reference to the buffer and file in their proper context. A file only changes when the user has committed changes with one of the write commands.

6.1.2. Switching to Edit Mode

The vi editor sports a range of options one can provide at start up, for the time being we will just look at the default startup. When invoked as shown above, the editor's default startup mode is command mode, so in essence you cannot commence to typing into the buffer. Instead you must switch out out of command mode to enter text. The following text describes edit start modes:

a     Append after cursor.
A     Append to end of line.
C     Change the rest of current line.
cw    Change the current word.
i     Insert before cursor.
I     Insert before first non blank line.
o     Open a line below for insert
O     Open a line above for insert.

6.1.3. Switching Modes & Saving Buffers to Files

Of course knowing the edit commands does not do much good if you can't switch back to command mode and save a file, to switch back simply hit the ESC key. To enter certain commands, the colon must be used. Write commands are one such set of commands. To do this, simply enter :.

Hitting the colon then will put the user at the colon (or command if you will) prompt at the bottom left corner of the screen. Now let us look at the save commands:

:w    Write the buffer to file.
:wq   Write the buffer to file and quit.

6.1.4. Yanking and Putting

What good is an editor if you cannot manipulate blocks of text? Of course vi supports this feature as well and as with most of the vi commands it somewhat intuitive. To yank a line but not delete it, simply enter yy or Y in command mode and the current line will be copied into a buffer. To put the line somewhere, navigate to the line above where the line is to be put and hit the p key for the put command. To move a line, simply delete the whole line with the dd command, navigate and put. Oops I Did Not Mean to do that!

Undo is pretty simple, u undoes the last action and U undoes the last line deleted or changes made on the last line.

6.1.5. Navigation in the Buffer

Most vi primers or tutorials start off with navigation, however, not unlike most editors in order to navigate a file there must be something to navigate to and from (hence why this column sort of went in reverse). Depending on your flavor of vi (or if it even is vi and not say elvis, nvi or vim) you can navigate in both edit and command mode.

For the beginner I feel that switching to command mode and then navigating is a bit safer until one has practiced for awhile. The navigation keys for terminals that are not recognized or do not support the use of arrow keys are the following:

k     Moves the cursor up one line.
j     Moves the cursor down one line.
l     Moves the cursor right one character.
h     Moves the cursor left one character.

If the terminal is recognized and supports them, the arrow keys can be used to navigate the buffer in command mode.

In addition to simple one spot navigation vi supports jumping to a line by simply typing in the line number at the colon prompt. For example, if you wanted to jump to line 223 the keystrokes from editor mode would look like so:


6.1.6. Searching a File, the Alternate Navigational Aid

The vi editor supports searching using regular expression syntax, however, it is slightly different to invoke from command mode. One simply hits the / key in command mode and enters what they are searching for, as an example let us say I am searching for the expression foo:


That is it, to illustrate a slightly different expression, let us say I am looking for foo bar:

/foo bar Additional Navigation Commands

Searching and scrolling are not the only ways to navigate a vi buffer. Following is a list of succinct navigation commands available for vi:

0     Move to beginning of line.
$     Move to end of line.
b     Back up one word.
w     Move forward one word.
G     Move to the bottom of the buffer.
H     Move to the top line on the screen.
L     Move to the last line on the screen.
M     Move the cursor to the middle of the screen.
N     Scan for next search match but opposite direction.
n     Scan for next search match in the same direction.

6.1.7. A Sample Session

Now that we have covered the basics, let us run a sample session using a couple of the items discussed so far. First, we open an empty file into the buffer from the command line like so:

# vi foo.txt

Next we switch to edit mode and enter two lines separated by an empty line, remember our buffer is empty so we hit the i key to insert before cursor and enter some text:

This is some text

there we skipped a line

Now hit the ESC key to switch back into command mode.

Now that we are in command mode, let us save the file. First, hit the : key, the cursor should be sitting in the lower left corner right after a prompt. At the : prompt enter w and hit the ENTER or RETURN key. The file has just been saved. There should have been a message to that effect, some vi editors will also tell you the name, how many lines and the size of the file as well.

It is time to navigate, the cursor should be sitting wherever it was when the file was saved. Try using the arrow keys to move around a bit. If they do not work (or you are just plain curious) try out the hjkl keys to see how they work.

Finally, let us do two more things, first, navigate up to the first line and then to the first character. Try out some of the other command mode navigation keys on that line, hit the following keys a couple of times:


The cursor should hop to the end of line, back to the beginning and then to the end again.

Next, search for an expression by hitting the / key and an expression like so:


The cursor should jump to the first occurrence of we.

Now save the file and exit using write and quit:


6.2. Configuring vi

The standard editor supplied with NetBSD is, needless to say, vi, the most loved and hated editor in the world. If you don't use vi, skip this section, otherwise read it before installing other versions of vi. NetBSD's vi (nvi) was written by Keith Bostic of UCB to have a freely redistributable version of this editor and has many powerful extensions worth learning while being still very compatible with the original vi. Nvi has become the standard version of vi for BSD.

Amongst the most interesting extensions are:

  • Extended regular expressions (egrep style), enabled with option extended.

  • Tag stacks.

  • Infinite undo (to undo, press u; to continue undoing, press .).

  • Incremental search, enabled with the option searchincr.

  • Left-right scrolling of lines, enabled with the option leftright; the number of columns to scroll is defined by the sidescroll option.

  • Command line history editing, enabled with the option cedit.

  • Filename completion, enabled by the filec option.

  • Backgrounded screens and displays.

  • Split screen editing.

6.2.1. Extensions to .exrc

The following example shows a .exrc file with some extended options enabled.

set showmode ruler
set filec=^[
set cedit=^[

The first line enables the display of the cursor position (row and column) and of the current mode (Command, Insert, Append) on the status line. The second line (where ^[ is the ESC character) enables filename completion with the ESC character. The third line enables command line history editing (also with the ESC character.) For example, writing : and then pressing ESC opens a window with a list of the previous commands which can be edited and executed (pressing Enter on a command executes it.)

6.2.2. Documentation

The misc installation set (misc.tgz) contains a lot of useful documentation on (n)vi and ex, and when installed it is available in /usr/share/doc directory. For example:

  • Edit: A tutorial - /usr/share/doc/usd/edit/edit.{ps.gz,txt}

  • Ex Reference Manual - /usr/share/doc/reference/ref1/ex/reference.{ps.gz,txt}

  • Vi man page - vi(1)

  • An Introduction to Display Editing with Vi by William Joy and Mark Horton - /usr/share/doc/usd/vi/vitut.{ps.gz,txt}

  • Vi/Ex Reference Manual by Keith Bostic - /usr/share/doc/reference/ref1/vi/vi.{ps.gz,txt}

  • Ex/Vi Quick Reference - /usr/share/doc/usd/vi/summary.{ps.gz,txt}

If you have never used vi, An Introduction to Display Editing with Vi by William Joy and Mark Horton is a very good starting point.

If you want to learn more about vi and the nvi extensions you should read the Vi/Ex Reference Manual by Keith Bostic which documents all the editor's commands and options.

6.3. Using tags with vi

This topic is not directly related to NetBSD but it can be useful, for example, for examining the kernel sources.

When you examine a set of sources in a tree of directories and subdirectories you can simplify your work using the tag feature of vi. The method is the following:

  1. cd to the base directory of the sources.

    $ cd /path
  2. Write the following commands:

    $ find . -name "*.[ch]" > filelist
    $ cat filelist | xargs ctags
  3. Add the following line to .exrc

    set tags=/path/tags

    (substitute the correct path instead of path.)