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 INTRODUCTION TO EDITORS

 Definition

                    An editor is general-purpose system software, which can be used to enter and /or modify text, program, figures or data

 Overview of Editing Process:

All interactive editors are computer systems program that allow user to create and revise a target document. The term document includes objects such as computer programs, text equations, tables, diagrams, line art and photographs, anything one might find on a printed page.

The interactive editing process is accomplished with the following tasks:

• The part of the target document that needs to be manipulated is viewed.

• The document is first displayed in the required format.

• Using the necessary designed tools, the document is modified.

• The view is updated appropriately and saved.

TYPES OF EDITORS

 Editors are broadly classified as:

          I.  Line Editors

2. Screen Editors

3. Graphic Editors

LINE EDITOR

                 A line editor edits a line at a time. Not more than one line can be edited at a time. Line number is used to accept the line for editing. A line editor may have the following features:

• Append line(s) of text: This feature allows adding lines of text to already existing text.
• Insert a line of text: A line can be inserted between any two lines of already existing text. Incrementing line numbers updates all the line numbers following the inserted line of text.
• Edit a given line: The given line can be brought on the screen with edit line command. The text can be corrected by moving the cursor to the right and left of the required character position to edit.
• Replace a line by another line: A new line can replace the required line number by typing the command.
• Delete a line: The required line can be deleted and the line number gets adjusted after deletion.
• List the lines of text: A set of lines can be displayed on the screen using the list-lines command.
• Save the file: The typed text can be saved in the secondary memory with a filename.  

There are different line-editors working on different operating system. Some of them are:

          CP/M System: EDIT

DOS System: EDLIN

UNIX System: ED

Line editors are always pointing to a single line in a file called the current line. When an existing file is accessed, the last line is made the current line so that the text can be appended easily. During editing session, the contents of a file are altered in a temporary buffer until creating or correcting the text is complete. When the existing file is edited, a copy of that file is placed in the buffer and changes are made to the copy. The changes have no effect on the original file until the buffer input is written into the file.

SCREEN EDITOR

                     In a screen editor, the user has control over the entire file. The user is free to make any changes and see them immediately on the screen or in the file. There are different commands to edit the text. Some of he commands are as follows:

Cursor Movement:

 Cursor Left: Cursor moves left by one character without deleting any character.

Cursor Right: Cursor moves right by one character without deleting any character.

Cursor Up: Cursor moves up by one line without deleting any character.

Cursor Down: Cursor moves down to the next line without deleting a character.

Word Right: Cursor moves to the next word to the right if it exists.

Word Left: Cursor moves to the next word to the left if it exists.

Cursor to the start of the file: The cursor is moved to the top left of the screen and it will be the first page from where the text is displayed.

Cursor to the end of file: The cursor moves to the bottom right of the screen and this screen will be the last part.

Cursor to the top of the screen: The cursor moves to the top left of the present screen.

Cursor to the bottom of the screen: the cursor moves to the bottom right of the present screen.

Cursor to start of the line: The cursor moves to the start of the present line.

Cursor to the end of line: The cursor moves to the end of the present line.

Page Up: Cursor moves to the previous page of display if it exists.

Page Down: Cursor moves to the next page of display if it exists.

Delete:

These commands is used to remove the characters.

A Line: The present line (where the cursor is at present) is completely deleted.

To the end of the line: From the present cursor position till the end of line the characters are deleted.

To the beginning of line: From the present cursor position till the beginning of the line the line characters are deleted.

Word Right: To the right of the cursor a word is deleted.

Word Left: To the left of the cursor a word is deleted.

Search:

These commands are used to search for a string.

Find: This is a command to place the cursor where the requested string is matched. If the string does not exist "not found" message is displayed.

Find and replace: This command is used to find the requested string and replace with the new string. If the requested string is not found, an error message is displayed.

File Services:

                   These commands are related to the file in secondary device.

Copy File: This command is used to copy a file from one to another file. The second file is a new file.

Delete File: The mentioned file is deleted from the secondary device using this command.

Append File: This command copies one-file contents to another. The second file contents will add after the first file content.

Save File: The file contents of the buffer are stored in the secondary device

with the filename.

Save As: The contents of the buffer are saved into the secondary device with the new filename

Load: The contents of the file mentioned are moved into the buffer and is put into viewing buffer.

Pick: If more than one file is loaded into the buffer, it is possible to view the one required by picking the file from the set of opened files.

New: Data typed can be stored into the secondary file by giving a name to it.

There are different screen editors available:

Some of them are:

VI Editor, Emac Editor - (Unix O.S.)

Norton Editor, Edit - (DOS)

Screen editor displays from one to many lines of text. Different varieties of screen editors are possible, based on the types of user interface used. They are:

1. Full screen window text editor: This editor uses the complete area of the display in the text mode. The user can make changes at the point of cursor.

2. Multiple Window Text Editor: The editor divides the screen into two or more windows to display different files in each window. The user can edit the text in one window at a time, but can see the contents of all the windows simultaneously. The user depending on the requirements can alter the size of the window.

GRAPHIC EDITOR

                     A graphic oriented editor is mainly used for creating and modifying picture. Graphic display allows control over every pixel (picture element) displayed on the CRT and typically display 480 rows x 640 pixels. Higher the display pixels, higher will be the resolution of the picture. There are different monitors available for higher resolutions. These displays extend the possibilities for user interfaces and can also support accurate imaging to produce on screen display that it facsimiles (exact copies) of type set documents.

Some of the features of graphic editor are:

• Use of mouse, joystick, and light pen can move the cursor to any point on the screen.
• Two points can be marked and a lie can be drawn with any flops.
• Joining many points polygon can be drawn. Example: rectangle, square.
• Selecting the required object can draw a circle and ellipse.
• Using the above object, complex diagram can also be drawn.
• Clipping, cutting and pasting of the object can also be done.
• Rotation about an axis and coordinates can be done.
• Scaling of objects can be achieved

 A few examples are:  

Corel Draw

AutoCAD  

Paint Brush

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