Emulating Terminals and Software

Certain terminals have the capability to emulate other terminals. If your terminal is not a valid type, check your owner's manual for possible terminal types your terminal can emulate.

Terminal emulating software (e.g. PC communication packages) may be used to interface with vi. Certain software packages use the Esc key for their attention interrupt. You will need to change the definition of this interrupt to one of the keys not used by vi (refer to the section on Unused Characters) or to an <ALT> key on your PC.

FILE RECOVERY

If you are in vi and for some reason you get logged off the system, use the recovery feature. Possible reasons are:

*  If the line to your terminal dropped.

*  If vi hung (will not respond) and you killed the session.

*  The system crashed gracefully (don't hold your breath!).

*  The system was shutdown by the super-user.

To recover a lost file you must first know whether vi "preserved" the file. The command to do this is:

     vi -r

A list of all lost files is displayed. If no files are displayed then you have no files available for recovery. If a file you need to recover is displayed, you must first change your present working directory to be the same as where the file is located. Then you can recover the file. For example, if you have a file, myprog.c, in your HOME/bin directory, to recover it you need to enter the following commands,

     cd $HOME/bin
     vi -r myprog.c

The file you are recovering must not have been modified since the date of preserve file. If you recover from an old preserve file, you can cause serious damage to your existing file.

Killing a vi Session

You may have to terminate a session of vi using the kill command. If vi hung or you where disconnected from the system for some reason and vi did not die from the hang-up, you will have to kill the session. To do this you must first find the PID of the vi process. The following code illustrates the necessary commands to find the PID and kill vi.

     $ ps -u mylogin | grep vi | nawk "{print $1}"
     1506
     $ kill -15 1506
     $ vi -r oldfilename

The ps command returns a PID number if there is a hung vi process, in this case PID 1506. The PID 1506 is a hung vi session. If there is no vi process hung, only your prompt will return. If a PID is returned, terminate it via the kill -15 1506 command. This causes vi to generate a preserve file for recovery. If no modifications were pending to be saved, then vi exits without preserving. If you had made changes, recover your file using the -r option.

---

NOTE:  If the system crashed, you might try to recover your lost file by using the -r option. This will work if vi had enough time to preserve your vi session to disk.

---

Delete/Interrupt Key

Press the Delete key to abort commands in vi. This may garble the screen, so be ready to use the Ctrl-R or Ctrl-L command to redraw the screen.

---

NOTE:  
If you press Delete while making a change (manipulation), you may need to use the u command (undo) to return to the condition before you began the change.

---

THE DISPLAY

Certain characters and lines are used to present a more understandable screen picture of the session buffer.

Command line for vi to create a new file.

     cj> vi text

Initial screen when vi is invoked for a new file:

The default number of lines used for the screen display depends on the baud rate of your terminal. The faster the baud rate, the larger the initial number of lines displayed. The lines beginning with a tilde (~) are not in the session buffer. This file currently has no lines in the session buffer. The last line displays information about the current file.

Since there is no text in the buffer, you cannot move the cursor. Therefore, you must press one of the insert keys and insert text.

MODES

The vi editor has three modes of operation. Each mode is a separate entity from the other two. You must be in command mode to issue commands to vi and to access the ex mode command line. You must be in insert mode to insert text. Thus you have to toggle between insert and command mode. The reason for this environment is simple: vi lets you use single keystroke commands. You do not have to twist your hand around to press some special control sequence to move the cursor around the buffer. Indeed there are some control characters used, some in command mode and a few in insert mode.

DEFINITIONS

Before continuing the discussion of vi it is necessary to understand the terminology relating to the editor. The following sections clarify some of the definitions and concepts of vi.

Units (Objects)

Units (often referred to as objects) of text are predefined amounts of text used by motion commands.

---

NOTE:  
A character preceded by a caret (^) that cannot have the cursor positioned under the ^ is a control character placed in the buffer.

---

Regular Expressions

Regular Expressions are patterns used to match strings in searches and substitutions. Refer to Module 113 on Regular Expressions.

Registers

The vi editor maintains various registers where text may be stored. Registers are used to save and retrieve text. You reference named registers with a single alphanumeric name. To access a register you place a double quote (") before the desired register name. For example, if you want to store a line of text in register "a" for later use, you type the following command,

     "ayy

This informs vi to place the next unit of text in the "a" register. The unit of text is the current line (yy, yank one line). Possible register names are unnamed/undo, numbered, and named.

The following table describes all of the registers and buffers used by vi.

Buffers

The vi editor uses a session buffer to maintain a copy of the file you are editing. There are two session buffers that you can switch between. For example, if you enter vi you can edit another file without leaving vi and then switch back and forth between the two session buffers. The following commands illustrate how you perform this simple task:

There are two session buffers. The current session and the alternate session. You reference the alternate session buffer by using the :e# command.

The following table describes the buffers used by vi.

---

NOTE:  
Each of the above buffers are dynamic ranging in size. The undo and numbered buffers are only affected by line changes and cannot be addressed for text storage.

---

Unused Characters

These characters may be used for the name of a string macro without interfering with existing commands. String macros are created using the :map command.

---

NOTE:  
Ctrl-Q is used for restarting output to terminal. Ctrl-S is used for stopping output to terminal; see Module 126 on stty. Systems with job control use the Ctrl-Z to suspend jobs.

---