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 <PageUp> and <PageDown> 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 <iostream> using std::cout; int main() { cout << "Hello, World, in C++." << 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“ /[hH]ello • search for "int" as a word (i.e. not print or sprint) /\<int\> • search for "eat" but not "beat" or "neat“ /\[^bn]eat

21. Replacing • replace "dog" with "cat" (first occurrence of dog) on the current line :s/dog/cat • replace "dog" with "cat" on lines 1 -> 3 (first occurrence of dog on each line) of the file :1,3s/dog/cat • replace "dog" with "cat" on lines 1 -> 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 editor’s insert mode, characters you type are inserted in the file • You have to remember all of the commands to be more efficient.