Chapter 3: The UNIX Editors

1
Chapter 3 The UNIX Editors

• ASCII and vi Editors

2
The vi EditorObjectives

• After studying this lesson, you should be able
  to
• Describe an ASCII text file
• Explain why operating system editors use ASCII
  files
• Create and edit simple documents using the vi
  editor

3
Program and Data

• Executable program files contain pure binary or
  machine language that the computer can
  immediately use or execute
• Data contains information. May be text, numeric,
  images, audio, video,
• Today, we limits our attention only to text and
  numeric data.

4
How files are stored?

• Both programs and data in UNIX are stored in
  files
• All information stored in files is in the form of
  binary digits
• A binary digit, called bit for short, consists of
  two numbers, 0 and 1
• The exclusive use of 0s (which mean off) and 1s
  (which mean on) as a way to communicate with
  the computer is known as machine language

5
ASCII Text Files

• To make information stored in files accessible,
  computer designers established a standard method
  for translating binary numbers into plain English
• This standard used a string of eight binary
  numbers, called a byte, which is an acronym for
  binary term
• Each byte, or code, has been standardized into a
  set of bit patterns known as ASCII codes
• ASCII stands for the American Standard Code for
  Information Interchange

6
ASCII Text Files

• Standard encoding scheme used to represent
  characters in binary format on computers
• Was 7-bit encoding, so 128 characters can be
  represented. (Now is 8-bit encoding, including
  Arabic, French, German, etc.)
• 0 to 31 ( 127) are "control characters" (cannot
  print)
• Ctrl-A or A is 1, B is 2, etc.
• Used for screen formatting data communication
• 32 to 126 are printable (95 printable symbols)

7
ASCII Characters
8
Example

• THE QUICK GREY FOX JUMPED OVER THE LAZY COWS.
• od -xc fox.txt

9
Is ASCII code enough?

• Is the ASCII code enough?
• No. Chinese or Japanese language text (thousands
  of symbols)
• Unicode
• A 16-bit coding scheme (allows for how many
  characters?)
• Developed by consortium of major American
  computer manufacturers, primarily to overcome the
  chaos of different coded character sets in use
  when creating multilingual programs and
  internationalizing software.
• ISO 32-bit code
• Developed by International Organization for
  Standardization
• Allows for (how many ?) characters

10
Using Operating System Editors

• Operating system editors let you create and edit
  simple ASCII files
• UNIX includes three editors
• vi
• Emacs
• pico
• We only cover vi Editor

11
vi Editor

• vi is not user-friendly! You have to remember
  all of the commands, in addition to which mode
  the editor is in.
• However, vi is very powerful and fast once you
  have mastered it.
• The vi editor remains the choice of most UNIX
  users

12
Using the vi Editor

• It is also a modal editor that is, it works in
  two modes
• Insert mode lets you enter text
• Command mode (default node) lets you enter
  commands to perform editing tasks, such as moving
  through the file and deleting text

13
Starting and Exiting vi

• Starting
• vi begin editing unnamed file
• vi file1.txt begin editing file1.txt
• Exiting (used only in command mode)
• q quit (assumes no changes made)
• q! quit, discard any changes that were made
• wq write the file, then quit
• ZZ write the file, then quit
• w newname write the file to 'newname'

14
Insert mode

• i (insert text before the cursor)
• a (insert text after the cursor)
• A (insert text at end of line)
• cw (change word)

15
Navigating

• Although the ltPageUpgt and ltPageDowngt and arrow
  keys work on some systems, I would strongly
  discourage their use. The following commands are
  guaranteed to work properly on all systems.
• vi equivalent
• Page Up F
• Page Down B
• Left Arrow h
• Right Arrow l
• Up Arrow k
• Down Arrow j
• Begin _
• End

16
Deleting

• delete current line dd
• delete from cursor to end of line D
• delete character under cursor x
• delete character before cursor (backspace) X
• Note that many of the above commands can be
  preceded by a number, for example
• 9x delete 9 characters
• 3dd delete 3 lines

17
Setting Line Number

• Show line numbers set nu
• Turn off line numbers set nonu
• display current line number/file name g
• go to line number 1 (go to line 1) G (go to
  last line in file)

18
Copying

• copy current line to "clipboard yy
• paste contents of "clipboard" below current
  line p
• paste contents of "clipboard" above current
  line P
• copy current line, and next 4 lines to
  "clipboard 5yy

19
Searching for a Pattern

• You can search forward for a pattern of
  characters by typing a forward slash (/), typing
  the pattern you are seeking, and then pressing
  Enter
• include ltiostreamgt
• using stdcout
• int main()
• cout ltlt "Hello, World, in C." ltlt endl
• return 0
• /World 6,19 All

20
Searching

• set case insensitive search set ic
• set case sensitive search set noic
• search forward (down) for "hello /hello
• search backward (up) for "hello ?hello
• search again, (same direction as original) n
• search again, (opposite direction as original) N
• search for "hello" at start of a line /hello
• search for "hello" at end of a line /hello
• search for "hello" or "Hello /hHello
• search for "int" as a word (i.e. not print or
  sprint) /\ltint\gt
• search for "eat" but not "beat" or
  "neat /\bneat

21
Replacing

• replace "dog" with "cat" (first occurrence of
  dog) on the current line s/dog/cat
• replace "dog" with "cat" on lines 1 -gt 3 (first
  occurrence of dog on each line) of the
  file 1,3s/dog/cat
• replace "dog" with "cat" on lines 1 -gt 3 of the
  file, every occurrence 1,3s/dog/cat/g
• replace "dog" with "cat" (every occurrence) for
  the entire file 1,s/dog/cat/g
• replace "dog" with "cat" (every occurrence) for
  the entire file (alternative method) s/dog/cat/
  g
• replace "dog" with "cat" (every occurrence) for
  the entire file but confirm each
  replacement s/dog/cat/gc

22
Latex

• A script language for editing documents
• Eample
• cp yzhu/public_html/cs251/tutorial.tex .
• latex tutorial
• dvips o tutorial.ps tutorial.dvi

23
Chapter Summary

• Bytes are computer characters referred to as
  codes
• These codes have been standardized and are known
  as ASCII codes
• The vi editor remains the choice of most UNIX
  users

24
Chapter Summary Continued

• The vi editor is a modal editor, because it works
  in two modes insert mode and command mode
• In the vi editors insert mode, characters you
  type are inserted in the file
• You have to remember all of the commands to be
  more efficient.