Unix, C Programming, and (X)HTML · 2019. 10. 24. · Unix-like systems: systems that work much...

Unix, C Programming, and

(X)HTML

Instructor:

Dr. Cong-Cong Xing

Access to Unix/Linux

Our Unix/Linux – (www.nicholls.edu)

telnet in MS Windows • Unsecured

• Not supported any more (by most Unix systems)

Putty – freeware, (telnet, ssh) • http://www.putty.nl/download.html

Login id and password • Id: ex: xing (lower case)

• Password: set it up (first time login)

Change your password • Type passwd at prompt

Exit Unix • Type: logout

Introduction to Unix

Some useful terms: • Bit: a binary digit, either 0 or 1

• Byte: a grouping of 8 bits

• Kilo (K): thousand (≈10^3)

• Mega (M): million (≈ 10^6)

• Giga (G): billion (≈ 10^9)

• Hertz: used to measure clock speed. 1 hz = 1 pulse per second. 3 Ghz = 3 billion pulse per second.

but in computing (esp. in terms

of storage)

symbol meaning roughly

Kilo K 210 (=1024) 103

Mega M 220 106

Giga G 230 109

Tera T 240 1012

Peta P 250 1015

Ex: What is the max memory locations

(in terms of bytes) can a 32-bit CPU

address?

232 = 22 210 210 210 = 4GB

32-bit long register

memory

• Flops: short for floating point operations per second. Also used to measure the speed of computers.

The origin of Unix (UNIX, officially) • Unix: The best OS people have written so far

• Dennis Ritchie and Ken Thompson from AT&T

• Multics – a failed OS, 1969

• GE, MIT, and AT&T (joint project)

• Space Travel – a game

• Space Travel rewritten on PDP-7

• Unix was born in 1971

• Naming: Unics (a pun on Multics) Unix

• Turning Award (1983)

• http://awards.acm.org/homepage.cfm?srt=all&awd

Unix and C

• Unix written initially in assembly language

(PDP series) (non-portable)

• In 1973, Unix was rewritten in C

• C was made for writing Unix

Major Components of Unix

• Kernel: master control program. It manages

resources and handles multitasking.

• File System: organization of data.

• Shell: interface between users and kernel. It

interprets user commands and passes them

to kernel.

• Utilities: software tools built in Unix.

kernel File sys

utilities shell user

what is shell (programming)?

Versions of Unix

• System V Unix ($): developed at AT&T.

AT&T Unix is the original Unix. Most Unix

systems on market are based on this. (e.g.

IBM AIX and Sun Solaris) (east coast)

• BSD Unix (%): modified at Berkeley and as

popular as AT&T Unix. (MacOS X is based on

BSD Unix) (west coast)

• Unix-like systems: systems that work much like Unix,

but do not use any part of AT&T Unix. (e.g. Linux and

Minix)

X Window System (X11)

• A GUI for Unix, developed at MIT (1984)

• X terminals: a hybrid I/O device, has CPU and

memory and can run X but not a complete computer in

itself. (early days, when I was at grad school)

• X terminal emulator: software simulation of X terminals

• (Is windowing the original Microsoft’s idea?)

Classic example of X window

Example: Mac OS X

X terminal in Mac OS X

Books?

• Any introductory Unix book can help

• Or, any online tutorial

• Understanding Unix by Stan Kelly-Bootle

• Unix for Dummies by J.R. Levine and M.L.

Your Unix Account

The system administrator creates your account (and delete your account).

System administrator is the “super user” who can access any user’s account

Your account info: • Account name (id)

• Password

• Home directory

• Group id: you may be assigned to a group of

users.

• Login shell

Terminals

• Called tty (abbr. for teletype) in Unix

• Putty (use telnet or ssh (recommend))

Getting Started

Use putty ssn or telent to login to eclipse

an old UNIX

server of our

Login to eclipse.nicholls.edu

Successful login shows:

login to web1.nicholls.edu

Telnet to server

Use Window’s (old version) telnet to

login to eclipse

• Start Run telnet

• Type o

• Type host-name

• type your id and password at prompt

Some useful commands

Shell prompt • $ -- Bourne shell, Korn shell, or bash shell

• % -- C shell or TC shell

• Will use $ throughout the slides

Script session, record whatever occurred • $script (to start a session)

• $exit (to end a session)

Password change • $ passwd

• Follow instructions

Trying out some simple commands • $ date

Fri Jan 20 11:26:24 CST 2006

• $ w (check who is on the system)

11:30am up 116 day(s), 20:30, 3 users, load average: 1.92, 1.70, 1.67

User tty login@ idle JCPU PCPU what

xing pts/6 9:11am 27 -bash

xing pts/7 11:08am w

root pts/4 10Oct05 2days bash

• $ whoami

• $ who

Email (built-in w/ Unix) • $ Mail <address> -- to send an email

• $ Mail -- to read emails

• Type x (or ^d or ^D) to quit reading emails

• Elm: a menu-driven e-mailer (not built-in, needs to be installed)

Unix manual • $ man <any command> -- manual page for the

command

Logging out

• $ logout or

• $ exit or

• $ ^D

• One of the above has to work

Spelling

• Unix or UNIX? The latter is traditional, the

former acceptable

Unix File System

File • Traditionally: a collection of related data

• Unix extends the traditional meaning of file

• To Unix, everything is a file (e.g., printer, disk drive, monitor, terminal, …)

File types • Ordinary files: common computer files

• Special files: device file, represent physical devices.

• Directory files: ordinary files and special files

are organized into directory files or

directories.

Ordinary files divided into two groups

• Text files: (also called ASCII files) contains

text and created/modified by text editors.

• Binary files: containing non-textual data.

Read and processed by programs.

Home and Working directories

• Home directory: the directory when you log in

the system.

• Each user has a unique home directory

• E.g.: /home/xing

• To go to home directory (from anywhere): $ cd

• Working directory: the current directory in

which you are working.

• Check what is your working directory: $ pwd

Unix File Tree

• Files in Unix are organized in the form of a

tree, typically as:

bin dev etc home tmp usr var

Users’ home directories

Root (/)

• Bin: short for “binary”. Contains shell software and common Unix commands

• Dev: short for “devices”. Holds device files.

• Etc: miscellaneous admin files (such as user list and passwords)

• Home: holds users’ home directories

• Tmp: temporary files are kept here.

• Usr: user-related files, on-line manual are kept here. home directories (for some version of Unix),

• Var: holds files whose contents varies

frequently. Ex: users’ mail boxes are typically

in /var/mail directory

File Names

• 1 – 255 character long, combination of:

• A – Z

• a – z

• 0 – 9

• period (.), underscore (_), dash (-)

• avoid using any special symbols and Unix

commands in file names.

Absolute pathnames

• full pathnames that identify the location of a

file in relation to root

• ex: (tree on next slide)

/home/al/cmps/hw1

/home/smith

smith al

cmps math

hw1 hw2

• ~ (tilde) represents the absolute pathname of

your home directory

• ~<username> represents the absolute

pathname of the home directory of that user

• three different ways to go back to your home:

• cd

• cd ~

• cd ~cxing

what does this

possibly indicate?

Relative pathnames

• relative to working directory

• . -- the current working directory

• .. -- parent of current working directory

• (Windows use the same thing)

• ex: given the previous tree, assume you are

at /home/smith, then $cd ../al/cmps/ changes

to cmps directory

Listing files

• $ ls -- list all files in working directory

• $ ls ../al/cmps -- lists all files in

/home/al/cmps (assume pwd is /home/smith)

Hidden Files and Directories

• a file or directory is hidden if it cannot be

listed by ls.

• $ ls -a -- to list all files and directories

Moving Files

• $ mv oldfilepathname newfilepathname

• ex: $ mv hw1 ../math/

( suppose at /home/al/cmps)

Copying Files

• $ cp filepathname1 filepathname2

• ex: $ cp hw1 ../math/

$ cp ./hw1 ../math/

( suppose at /home/al/cmps)

Creating Files by Redirecting

• redirect from the “standard output”

• ex: $ ls > file1 -- result is saved in file1

• note: redirection into an existing file overwrite

the file

• “double redirection” >> fixes the problem:

• $ ls >> file1 -- result is appended to file1

Links (hard, and symbolic)

• One file may have more than one name

• Each file has a unique i-node – an internal

data structure representing the location (disk

sector) of the file, the mode of the file,

creation date & time, and other info.

• A (hard) link is a name that refers to a file’s i-

• A link is created using the ln command

• Ex: $ ln existingfn newfn

• A symbolic link is a name that refers to

another (file) name.

• Ex: $ ln –s exitingfn newfn

i-node

hard link to

symbolic link to

deletion of name1

will have no effect

on name2 (or 3), but

does affect name4

ts.txt is a

symbolic

link to t.txt

after t.txt

removed,

symbolic

is “broken”

the file dsf has

been removed.

dsf-link is ok,

but not dsf-s-

Long Listing

• More info about files can be shown by

$ ls –l

drwxr-xr-x 2 xing staff 512 Jan 23 11:40 t

-rw-r--r-- 1 xing staff 8 Apr 26 2004 test

drwxr-xr-x 2 xing staff 512 Aug 24 00:06 test1

drwxr-xr-x 2 xing staff 512 Jan 23 11:40 test

Access

control

(hard)

owner group Size

(byte)

Date &

• File access control:

• First 3 symbols control what owner can do

• Next 3 symbols control what group can do

• Last 3 symbols control what public can do

• for first position: d means directory

- means file

l means (soft) link

• r (read) – examine (but not change) the contents of

a file

• w (write) – change the contents of a file

• x (execute) – run the file (program)

• ex:

rwxrwx--- owner and group users have

read, write, and execute privileges,

public has no privileges

r--r--r-- everyone has read privilege only

changing file modes (1)

• u – user (owner)

• g – group

• o – others (public)

• a – all (owner, group, public)

• = -- assign a permission (remove others)

• + -- add a permission

• - -- remove a permission

• ex:

• $ chmod u+x filename

add execution to user

• $ chmod g-rw filename remove read, write

permission from group

• $ chmod a=r filename

add read to everyone and remove anything else

• $ chmod u=rw,go=r filename (no space ..w,g…)

give user read and write, everyone else read

changing file modes (2) • for each position, 1 indicates yes (permitted),

0 indicate no (not permitted)

• ex: r--r--r-- is denoted by 100100100

• break down into 3 parts and regards each part a binary number, and convert it to decimal

• then r--r--r-- can be denoted as 444

(1002=410)

• more ex: rwxrwxrwx = 777

111 111 111

rwxr--r-- = 744

111 100 100

rw-rw---- = 660

110 110 000

--------- = 000

000 000 000

chmod 777 filename

chmod 442 filename

Conversion between binary and

decimal numbers

1112 = 1 × 22 + 1 × 21 + 1 × 20 = 710

1102 = 1 × 22 + 1 × 21 + 0 × 20 = 610

11102 = 1 × 23 + 1 × 22 + 1 × 21 + 0 × 20 = 1410

2= 3 𝑟 0

2= 1 𝑟 1

2= 0 𝑟 1

610 = 1102

2= 7 𝑟 0

2= 3 𝑟 1

2= 1 𝑟 1

2= 0 𝑟 1

1410 = 11102

proof that this conversion

scheme always works?

Working with Files

Printing a calendar • $ cal

-- print current month

• $ cal month year

– prints the given month of the given year

-- ex: $ cal 12 2007

• $ cal year

-- prints the entire year

-- ex: $ cal 2006

Viewing Files

• $ cat fname

-- (catenate) contents of a file (all the way to the end

of a file)

• $ more fname

-- display contents of a file (page by page)

-- type q to quit viewing

• $ less fname

• $ page fname

-- similar to more

Concatenating Files

• $ cat file1 file2 ….

-- displays file1 followed by file2 …

• try/ex: $ cal 6 2007 > june-2006

$ cal 7 2007 > july-2006

$ cat june-2006 july-2007

$ cat june-2006 july-2007 > sum-2007

$ more sum-2007

Appending to a File

• $ command >> fname

result produced by command is appended

to the end of fname

• try/ex: $ cal 8 2007 >> sum-2007

Deleting Files

• $ rm fname -- remove fname

Copying and Moving Files

• $ cp fn1 fn2 $ mv fn1 fn2 (see previous slides)

Working with Directories

Creating a directory • $ mkdir dn --- creates a dir w/ name dn

• try/ex: $ mkdir cmps

Removing a directory • $ rmdir dn --- remove the dir dn

Changing working directory • $ cd dn --- switch to dir dn

Returning to the home directory

• $ cd or

• $ cd ~

Printing your working directory path

• $ pwd

Unix common shells

name what when where who

Bourne shell

Original

1979 AT&T Steven Bourne

Korn shell

Improved

1986 AT&T David Korn

Bourne again

shell (bash)

Improved

1988 GNU project Brian Fox, Chet Ramey

C shell (csh) BSD Unix 1979 UC Berkely Bill Joy

TC shell (tcsh) Improved

1980 CMU, Ohio

Ken Greer, Paul

Placeway

Debian

Almquist shell

(dash)

Decendant

Almquist

Shell (ash)

rename)

BSD Kenneth Almquist

Your login shell • Shown (maybe) at the command line prompt right

after login, if not

• Check what your login shell is

• $ ps

• Or, read contents of /etc/passwd

• Ex: $ grep cxing /etc/passwd

• Or, $ echo $SHELL

• Or, $ echo $0 (current shell)

• Set up by the administrator

• To change your login shell: chsh

• $ more /etc/shells (to see available shells)

• $ chsh /bin/tcsh (to change to tcsh shell)

• $ chsh (follow instructions)

• $ chsh –s /bin/tcsh cxing (follow instructions,

change to tcsh shell)

How Shell Processes Commands

Shell displays

prompt (e.g. $) –

ready to receive

commands

User types

A command

User types

return (end

of command)

shell interprets

the command

(looking for prog)

Kernel runs the

program and shell

“goes to sleep”

shell “wakes up”

when prog

finished. display

prompt again

Options and Arguments

• options are switches that modify what a

command does.

• the fname that follows a command is referred

to as an argument.

• ex: $ ls -a -l fname or $ ls –al fname

check man for option info of a command

• common options for ls

-a All files including hidden files

-l Long listing.

-F Flag the files. / after dir, * after exeutable

-r List files by reverse order

-h Sizes are scaled to be readable

-d List dir name (not its contents) when

argument is a dir, often used w/ -l to see the

status of a dir

Standard input, output, and error

• (remember ) : everything is a file to Unix

• standard input: the file where programs look

for input. (keyboard by default)

• standard output: the file to which programs

send output. (monitor by default)

• standard error: the file to which programs

send error messages. (monitor by default)

Redirection revisited • $ cal 2007 output is sent to standard

output – terminal monitor

• $ cal 2007 > cal.file standard output is redirected (to cal.file). output is sent to cal.file

• Mail xing input is taken from the standard input – keyboard

• Mail xing < afile standard input is redirected to afile. Input is taken from afile.

Grouping commands

• c1; c2;... cn commands are executed one by

one consecutively.

• ex: $ w; ls; cal has the same effect as

• grouping can be useful in redirection

• ex: create a calendar for summer of 2007

with grouping

$ (cal 6 2007; cal 7 2007; cal 8 2007) > sum2007

w/o grouping

Piping • c1 | c2 connects the output from c1 to the

input of c2

• ex: $ cal 2007; cal 2008; cal 2009

(scrolls too fast)

$ (cal 2007; cal 2008; cal 2009) | more

(one screen at a time)

$ ls | more

the output of ls is connected to the input of more

stdout file

tee file -- copies whatever in/from stdin to stdout, and to

file at the same time

What entered w/

return (stdin)

(response to

input : stdin is

sent to stdout .

^d to finish)

the file ss has a copy of stdin

command1

outfile command2

$ command1 | tee outfile | command2 (two pipes, one tee)

Output from command1 goes to file outfile and to stdin of command2

• Ex:

$ (cal 2008; cal 2009) | tee mycal | more

Filters

• A filter refers to a utility which takes a stream

of data from stdin, transform the data in some

way, and sends the result to stdout

• Ex: cat, more, less, pg, wc, nl

ex: nl – add line-numbers

cygwin – a Unix-

like environment

in Windows

Wildcards

• Characters that can stand for other characters

• *, ?, []

• * -- stands for any sequence of symbols

• ? – stands for any single symbol

• [] – stands for any symbol included in the bracket

• Ex:

• ls *.exe

• ls *year*

• ls temp?

• ls temp[abc]

• ls *[m-z]

• ls –ld *[m-z]

Quoting Special Characters

• Under some shells (e.g. csh), special attention need to

be made to echo special symbols

• ex: % echo What time is it?

% echo: No match.

• to fix this problem

Quote Effect

\ Cancel the special meaning of next character

‘xxxx’ Cancel the special meaning of xxxx

“xxxx” Similar to ‘xxxx’, except for $, ``,and \

`xxxx` Execute the command xxxx

• $ echo what time is it\?

• What time is it?

• $ echo what time is it`date`

• what time is itMon Aug 13 ……

Background processing • Under Unix, a process can run in foreground or

background.

• To run a process in background

$ command &

ex: $ sleep 60 & (sleep 60 seconds)

[1] 1865

where: [1] --- job #

1865 --- process id (PID)

• At command line, ^c to terminate process, ^z to suspend a process.

• To terminate a process:

$ kill pid kill -9 pid surely kill

$ kill %n (n is the job #) kill -9 %n surely kill

• some useful commands

bg %n send process n to background

fg %n bring process n to foreground

jobs list jobs status

kill %n terminate process n

stop %n suspend process n

ps show status of all processes

note: some commands may only work under certain shells

Summary of job controls

Fg running

process

Suspended

process

Bg running

process

To bring it to

foreground

Nothing Fg it Fg it

To send it to

background

Suspend it

and bg it

Bg it Nothing

To Terminate ^c or

^z then kill it

Kill (-9) it kill (-9) it

To suspend ^z Nothing stop it(pid)

bring a foreground process to background

bring a background process to foreground

History and filename completion

• $ history lists recently typed commands

• $ !# To re-run a command, # is the

number

• $ !! to re-run last command

• Trick

• Under csh, tcsh, bash, filenames can automatically

be completed by hitting the tab key

To check your login shell • ps or

• echo $SHELL or

• echo $shell

To leave a shell • $ exit or $ logout

ftp and telnet (or ssh) • built-in Unix utilities

• telnet (or ssh): remote login to a networked computer

• ftp (sftp): file transfer protocol

• $ telnet hostname

• $ ftp (sftp) id@hostname [-port]

• get – download files

• put – upload files

• ascii – set to ascii transfer mode

• binary – set to binary transfer mode

• bye (or quit) – to end ftp

• MS Windows

• ftp and telnet also exist in (old) MS Windows

• they work similarly as in Unix

• for ftp, an easier way may be to use the GUI

program, e.g.:

• free software WinSCP, filezilla

• open My Computer | type hostname in the address

• open a web browser, type the hostname in the

URL bar

Free FTP software

• WinSCP

• https://winscp.net/eng/download.php

• filezilla

• https://filezilla-project.org/

WinSCP

Free Unix shell account?

Free Unix account: sdf.org

Command Summary

echo $SHELL or echo $shell check login shell

shellfile run shell specified in shellfile

exit exit a subsell

!n repeat nth command

!! repeat last command

fil <tab> complete file name starting w/ fil

^c kill a foreground process

^z suspend a foreground process

bg %n send job n to background

fg %n bring job n to foreground

jobs list status of all jobs

kill pid kill process w/ id being pid

kill %n kill job n

kill -9 %n definitely kill job ns

stop %n suspend background job n

wc file count lines, words, and characters in file

sort file sort lines of file in usual order

sleep n sleep n seconds

command & running in background

ps obtain process status

mkidr dir make directory

mv fi dir move file fi to directory dir

cd dir change to directory dir

cd change to home directory

rmdir dir delete directory

pwd print working directory path

cal m yr show calendar for month m in year yr

cal yr show calendar for year yr

ls list files in working directory

cat fi show contents of file fi

more fi show contents of file fi, one screen at a time

pg fi similar to more

cp fi1 fi2 copy file fi1 to file fi2

mv fi1 fil2 move file1 to asked

rm fi delete file fi

chmod spec fi change permission status of file fi

passwd change your password

date print current date

w check who is on the system

man comm check the manual for command comm

logout logout system

exit logout system

^d logout system

(s)ftp File transfer (upload and download)

telnet remote login

ssh Secure remote login

Example of real-world state-of-

the-art research (NFV-SONATA)

Text Editor – Vi (or Vim)

To invoke vi

• $ vi fname

Unix shell

Command

Insert mode

vi fname

i, o esc

Basic commands

• i ---- go to insert mode

• esc --- go to command mode

• h --- move left

• j --- move down

• k --- move up

• l --- move right

• o --- go to insert mode, move to next line

Why choose “i”, “h”, “j” ,“k”,

“l”,.... ? ---Nearby finger tips

Left index

finger

right index

finger

• x ---- delete one character

• dd --- delete entire line

• 0 (zero) – move cursor to the start of a line

• $ -- move the cursor to the end of a line

• u --- undo most recent change

• :q! --- quit w/o saving

• :x --- quit w/ saving

More commands • :w --- save file w/o quitting

• a --- append text, go to insert mode

• J --- join current line w/ the next line together

• :w fname --- save file to fname

• “copy & paste” – yank and put • (do the following in command mode)

• ma (at the beginning of block, mark)

• y'a (at the end of block, yank)

• p (put what being yanked, put)

Spell checking (may be unavailable…)

• $ spell fname

• $ ispell fname

Search

• :/ pattern --- find occurrence of pattern

• :/ <return> --- repeat last find

• :? pattern --- works like /, but backwards

• :? <return> --- works like /, but backwards

global substitution

• :%s/old/new/g --- replace every occurrence of

old by new in the file

Number line

• :set nu :set nonu

Jumping around

• nG --- jump to nth line

• G --- jump to bottom

command line editing using vi

• % bindkey –v (tcsh shell)

• $ set –o vi (bash )

• ex:

• $ echo I havee mad a mistake

press <esc> to enter vi mode move the cursor to

“havee” to fix it

press <return> to execute the command

Networking

Terms • LAN – Local Area Network

• WAN – Wide Area Network

• Unix was designed to be a network-oriented OS (back in what year?)

Network Topology • Bus

• Ring

• Star

Internet History

• (see http://en.wikipedia.org/wiki/Internet)

Internet Protocols

• Protocols --- data communication rules

• TCP – Transmission Control Protocol

• IP – Internet Protocol

• PPP --- point-to-point protocol

• SLIP – serial line internet protocol

High speed

Low speed

IP Address and Domain Name

• IP address: four numbers separated by “.”

• Each host on the Internet has a unique IP

• ex: 128.46.126.96

• Each host can also be identified by its domain

• Ex: juno.eecs.tulane.edu

host subnet

organization

Top-level

domain

• Common top-level domains • com – commercial organization

• edu -- school

• gov -- government

• mil -- military

• org – nonprofit organization

• net – network support organization

• Country names • ca – Canada ch -- Switzerland

• cn – China fr -- France

E-mail (built-in in Unix)

• mail – original

• Mail – Berkeley mail

• mailx – System V mail

• elm – alternative to standard Unix mailers

• pine – similar to elm

Check to see if one has read his mail

• finger userid

• ex: finger xing

Common Mail Conventions • :-) -- smile

• ;-) -- wink

• :-( -- frown

(26) xing@eclipse> finger xing

Login name: xing

Directory: /home/xing Shell: /bin/tcsh

On since Feb 17 05:49:55 on pts/2 from ip68-11-69-123.no.no.cox.net

New mail received Thu Feb 16 11:47:38 2006;

unread since Tue Feb 14 15:20:30 2006

Classic Unix Network Utilities

• rlogin -- remote login

• telnet – remote login

• ftp – file transfer (protocol)

• rcp -- remote copy

Basic ftp commands (putty has sftp – psftp)

• ? (or help) -- for help

• ascii – for ASCII file transfer

• binary – for binary file transfer

• put fn --- upload file fn (send)

• get fn – download file fn

• mget fn – multiple get

• other Unix commands also work under ftp , such as

• cd, pwd, ls

• Anonymous ftp (public ftp)

• Loign name: anonymous or guest

• Password: none

• Ex: ftp.census.gov

ftp.cac.psu.edu

A problem with ftping files between

Windows and Unix.

• Windows text files (say, generated by

Notepad) will show ^M or ^[ at the end of each

line when displayed in Unix.

• How to fix it? Type the following

• tr –d ‘\015’ < inputFile > outFile

Octal for ^M

CR (carriage return) Input file name Output file

‘\015’ can be

replaced by ‘\033’

(octal for ^[ (ESC))

• How to find octal for other control characters?

• In vi insert mode, type <ctrl-v>, then type the

<ctrl-character>, then save the file (as fileName).

• Then, at the command line, type the following to

see the octal

• od –b fileName ( option –a to see name, not otcal)

• http://www.neurophys.wisc.edu/comp/docs/ascii/ to

check binaries, octals, etc…

• http://www.unix-manuals.com/refs/misc/ascii-

table.html

World Wide Web (WWW)

• A way of presenting info on the Internet in the

form of hypertext documents.

• WWW ≠ Internet (why not?)

• When was WWW born?

• Was WWW designed by computer scientists?

• Was WWW designed in the U.S. (as the

Internet)?

• How does WWW work?

• Client-server model

• URL (Uniform Resource Locator)

• http://www.nicholls.edu

• ftp://eclipse.nicholls.edu (what does the header “http” or

“ftp” mean?)

client server

request

answer

• Specifically, • You instruct the client program (the browser, e.g.

IE or Firefox) on your local computer to get a Web document.

• The client locates the remote Web site.

• The client sends a request over the Internet to the server.

• The server on the Web sends a copy of the document you specified.

• The client program formats the document and displays it.

File Compression and Archive

• Common file compressions

Compression Decompression Suffix exampe

compress uncompress .Z file.Z

gzip gunzip .gz file.gz

pkzip pkunzip .ZIP file.ZIP

tar (tape

archive)

tar .tar file.tar

• $ gzip fn – compress file fn

• $ gunzip fn – uncompress file fn

• $ tar –cf fn.tar dir (or files)

• – create an archive file fn.tar from dir or (files)

• $ tar –tf fn.tar

• list contents of the archive

• $ tar –xf fn.tar

• restores the archived directory

ZIP files w/ password protection

make sure zip is installed on your OS

ZIP files w/ password protection

on my Mac OS

Computer Security

Cryptography

• Plaintext: original unencrypted text.

• Ciphertext: encrypted text.

• Algorithm: transform plaintext into ciphertext

(and vice versa). (need MATH here!)

• Key: info, such as a word, a phrase, required

to encrypt or decrypt a message.

Encryption scenarios

• Secret-key encryption (aka: symmetrical

encryption):

use the same (shared secrete) key to encrypt and

decrypt a message

How to send the

secret key over

the Internet?

• Public-key encryption (aka: asymmetric

encryption):

• message is encrypted using public key (by the sender)

and decrypted using the private key (by the receiver).

• the public-key and private key are a matching pair

• public-key is used to encrypt messages.

• private-key is used to decrypt (public-key-encrypted)

messages.

• no other possibilities (this is the only way to work)

no need to send the

key over the Internet

• Public-key authentication (prove you are who you

claim you are): client sends request to server asking

for access, server encrypts a challenging message

using the public key and return it to the client. If the

client is able to understand the encrypted message,

then it proves that it holds the associated private key.

plaintext ciphertext

ciphertext plaintext

alg Internet

secret-key encryption

sender

receiver

alg Internet

public key

private key

sender

receiver

public-key encryption

alg Internet

private key

public key

public-key authentication

client

server

RSA RSA RSA

RSA (the 3 MIT people) • The most well-known public-key encryption algorithm

• Based on the fact that there is no (currently) efficient way to factor a large number

• Industrial-strength de facto standard

• Built into web browsers (IE and others) and other software products

• RSA= Rivest, Shamir, and Adleman in 1977

• ACM Turing award winners!!!

• Restricted by US government for exporting to foreign countries (really?)

ssh (secure shell) vs. telnet • both ssh and telnet are remote login utilities.

• telnet = plaintext (becoming/already obsolete)

• ssh = ciphertext, offers RSA public-key authentication. It also offers userid-password combination.

• to use ssh in Unix:

% ssh <hostname>

public-key authentication w/ ssh

• conventional authentication : password

• secure authentication: public-key

• In Unix,

• generate a key pair: % ssh-keygen

and follow the instructions.

• copy the public key to the remote host, append it to

the file ~/.ssh/authorized_keys

ssh-keygen screen shot

• change file permission:

• % chmod u=rwx,go=rx ~/.ssh

• % chmod u=rw,go=r ~/.ssh/authorized_keys

• ready to go:

• % ssh user-name@host-name

• note: once public-key auth is set up, passwd auth will disappear (not needed)

• In PuTTY

• Refer to the handout (Putty manual) or

• http://the.earth.li/~sgtatham/putty/0.55/htmldoc/Chapter8.html

Open putty-keygen, choose ssh2RSA

Generate the key-pair

save the private key to somewhere in your hard drive

Save the public key (may be optional)

(or, newer)

telnet to eclipse (the server), append the public-key to the file .ssh/authorized_keys in your home directory. (create such a file if you do not have one)

Make sure no one has right to write authorized_keys except you. (chmod go-w authorized_keys)

Logout eclipse (the server)

Open putty, put eclipse.nicholls.edu in the host name field

Make sure ssh is selected

Click the Auth under Connection-SSH, click the browse button to open your private key file

Select “keyboard-interactive” (ssh2) for authentication methods

Click open button to start the login. (Note: eclipse will not ask you password for authentication, instead, a short message about public-key auth is displayed)

Click here

here to

locate pk

(or, newer)

WULA!!! WULA!!!!

I can relax now.

(or, newer)

WULA!!!!

Again!.

WULA!!!!

the 3rd time!

or, unfortunately,

More about public-key authentication

and password (authentication)

The following is taken from

http://winscp.net/eng/docs/public_key

Public key authentication is an alternative

means of identifying yourself to a login

server, instead of typing a password. It is

more secure and more flexible, but more

difficult to set up.

In conventional password authentication,

you prove you are who you claim to be by

proving that you know the correct password.

The only way to prove you know the

password is to tell the server what you think

the password is. This means that if the

server has been hacked, or spoofed, an

attacker can learn your password.

Public key authentication solves this problem. You

generate a key pair, consisting of a public key

(which everybody is allowed to know) and a private

key (which you keep secret and do not give to

anybody). The private key is able to generate

signatures. A signature created using your private

key cannot be forged by anybody who does not

have that key; but anybody who has your public key

can verify that a particular signature is genuine.

How does SSH work?

Symmetric keys are used by SSH in order to encrypt

the entire connection. Contrary to what some users

assume, public/private asymmetrical key pairs that

can be created are only used for authentication, not

the encrypting the connection. The symmetrical

encryption allows even password authentication to

be protected against snooping.

How does SSH work?

After the symmetrical encryption is established to

secure communications between the server and

client, the client must authenticate to be allowed to

access the server. The server can use the public key

in the relevant file to encrypt a challenge message to

the client. If the client can prove that it was able to

decrypt this message, it has demonstrated that it

owns the associated private key. The server then

can set up the environment for the client.

Now, relax and enjoy state-of-the-art

security, the Turing-award-winning RSA!

Wait a minute…

Quantum computing can break it!!!

what ???

FYI: Why didn’t Bill Gates

receive Turing Award?

Which of the following brilliant ideas which have significant impacts on our life is originally from Microsoft (Bill Gates)?

• GUI for OS (windowing)

• Internet, TCP/IP

• Email, ftp

• WWW, http, html

• Scripting html document

• Web browser (graphical and non-graphical)

• Security, RSA

• Fundamental computer architecture

Answer : 0. Bill Gates is a (successful) businessman rather than a computer scientist

• GUI for OS: Mac had GUI before Windows

• Internet, TCP/IP: back to 1960-70

• Email: Internet utility, ftp: Internet utility

• WWW, http, html: Tim Berners-Lee, CERN • http://www.cern.ch

• Scripting html document: JavaScript, Netscape

• Web browser (graphical and nongraphical): Netscape (Mosaic)

• Security, RSA: obvious

• Computer fundamental layout: John von Neumann • http://www-groups.dcs.st-

and.ac.uk/~history/Mathematicians/Von_Neumann.html

Unix Startup Files

Startup Files allow users to customize working environment

Types of Startup Files • System-wide startup files

• Created by system administrator

• Contains commands to be used by your login shell

• Executed (if exist) first by your login shell.

• Login initialization files • created by users

• resides in your home directory

• executed when users login

• Shell initialization files

• created by user

• resides in your home directory

• executed when a subshell starts up (whether it is a

login shell or not)

System-wide Startup Files

• Reside in /etc (typically)

• File name depends on login shell

• sh, ksh, bash

• /etc/.profile

• csh, tcsh

• /etc/.login, /etc/.cshrc, /etc/csh.login, /etc/csh.cshrc

Login Initialization Files

• Depends on login shell

• sh, ksh, bash

• .profile

• csh, tcsh • .login

Shell Initialization Files • Also called environment files

• Executed whenever a subshell is invoked

• Name depends on shell (name) • sh does not have a shell initialization file

• ksh : .kshrc

• csh: .cshrc

• tcsh: .tcshrc; if .tcshrc not found, look for .cshrc

• bash: .bashrc

Order of Execution

• system-wide startup file

• shell initialization files

• login initialization files (order of last two may vary depending on systems)

Variables

• Values of variables are setup in startup files to

customize the working environment

• Types of variables

• environment variables: predefined system shell

variables

• user-defined variables: personal variables created

by users

Common Environment Variables

HOME Pathname of your home directory

PATH Directories where shell looks for commands

SHELL Pathname of your login shell

TERM Your terminal type

MAIL Pathname of system mail

USER Your user name

HOST The server’s name (or ip address)

Setting Environment Variables (for the current

session)

• depends on shell

• sh, ksh, bash • ex: TERM=vt100

• csh, tcsh • ex: setenv TERM vt100

Listing Values of Environment Vars • sh, ksh, bash

• set

• csh, tcsh

• setenv

Check the value of a specific Environment

Variable

• ex : echo $TERM

echo $SHELL

Special Variables of csh and tcsh

• csh and tcsh use the same environment variables as

the sh family. (e.g. HOME) (all capitals)

• But csh and tcsh also have their own special

variables (e.g. home) (all lower-case)

pwd pathname of current working directory

history size of history list

home pathname of home directory

path dirs where shell looks for commands

term terminal type

shell pathname of shell

user your user name

prompt current prompt symbol

• note: some variables have a uppercase counterpart as environment variable (e.g. home). For such variables, if their values are changed, their uppercase counterparts will be changed too (and vice versa, at least under tcsh. Note: commands for setting env vars and special vars are different )

• To list the values of all special variables (under csh/tcsh) • % set

• To set value of special variable (under csh/tcsh) • % set <var> = <value>

User-defined Variables • To define your own variable, in .login (and .cshrc) add:

set <your-var> = <value>

ex: set web = /home/xing/public_html

(note the usage difference between set and setenv)

• To define your own variable, in .profile add:

<your-var>=<value>

ex: web=/home/xing/public_html

• To use the newly defined variable

• % ls $web (note the $ )

• % cd $web (note the $)

Calendar Utility (questionable in Linux) • don’t confuse it w/ cal utility

• In .login (or .cshrc), add the line

calendar

• create a file named calendar in your home which contains a line involving today’s or tomorrow’s date.

• To run .login w/o logout, type

source .login

History Utility

• % history

• gives some previously typed commands

• % !n

• to re-execute the command, where n is the number or the first

letter of the command you look for.

• % !!

• Execute the last command

• size is adjustable

• in .login and/or .chsrc add

set history = n (n is a number)

Aliases

• used to shorten long command

• ex: in .login and/or .cshrc add

alias h “history”

• In .login and/or .cshrc add

alias rem “/bin/rm –i”

• rem will prompt you with yes/no, so it is a way to safely remove files.

Comments

• lines start with #

Shell Scripting

What is a shell script? • A file that contains some shell commands and

is to be executed by the shell.

• Ex: # a simple script: shs

How to execute shell scripts?

• suppose shs is the name of above script

• submit shs as an argument for sh (or other

shells, csh, bash,…)

• % sh shs (or % csh shs)

• or

• % chmod u+x shs (mark shs executable)

• % shs (or ./shs)

Now you are scripting!!

Subshells • when a script is executed, the login shell

actually calls another shell (a subshell) to process the script.

• Regardless of your login shell, you may use any shell to process your shell scripts.

• To specify which shell to use to process a script file, add the following line at the top of your script file. • #!/bin/<shell> <shell>=sh, csh, tcsh,…

• ex:

#!/bin/sh

# a shell script

• note

• #! is “one” character, cannot be separated

(#! is called “shebang” )

• blank space and new-line space matter here!

Shell as a programming language

• Variables

• Input/output

• Arithmetic operations

• Conditional expressions

• Selection structures

• Loop structures

Variables • Three kinds of variables can be used in shell

scripts.

• Environment variables: • e.g. HOME

• User-defined variables: • for users’ own needs

• Positional parameters: • store values from command-line arguments

Positional parameters • indexed from 0 to 9: 0, 1, 2, …, 9

• $0 holds the filename of the script, $1 holds the first argument, S2 the second argument, $3 the third argument, … following the script file name

• ex:

#!/bin/sh

# a shell script, name: shs0

echo $0 $1 $2 $3

• run this script with (shs0 is the filename of the

script)

% shs0 i like it

$0 $1 $2 $3

arguments

• Two special positional parameters

• $* -- lists all command-line arguments

• $# -- gives the number of arguments

• $0 is not considered an argument (here), but is the

file name (or command)

• ex:

echo “you typed” $# “arguments:” $*

• as a simple application, we can write a script that changes a file’s executable mode.

#!/bin/sh

# change a file’s executable mode

chmod u+x $1

echo $1 ‘can be executed now’

ls -l $1

Save it as “myscript”, it can make itself executable

% sh myscript myscript

Set command and positional parameters • set can be used to assign values to positional parameters.

• the whole set of “original” arguments (if any) following the script name will be replaced by that produced by the set command

• ex:

set `date` # note the ` and ` pair, the command

# date will be executed

echo “Time:” $4 $5

echo “Day:” $1

echo “Date:” $3 $2 $6

command date produces

Fri Aug 20 10:33:34 EST 2005

which is caught by set and consequently assigned

$1 $2 $3 $4 $5 $6

Labeling output from wc • $ wc <file>

gives the number of lines, number of words, and

number of characters in, and the name of <file>

• ex

$ wc lab1

5 17 84 lab1

• want to write a script “mywc”, s.t.

$ mywc lab1

shows:

File: lab1

Lines: 5

Words: 17

Characters: 84

How can we do this?

• #!/bin/sh

# label output from wc

set `wc $1` # execute wc $1 and put the result

# as the positional parameters

echo “File: $4”

echo “Lines: $1”

echo “Words: $2”

echo “Characters: $3”

User-defined variables • combination of lower case letters, upper case letters,

underscore, and digits.

• first character cannot be digits

• ex: a, b1,c2, f_var

Assignment • <var>=<value> (no space in assignment)

• Ex: a=“this is a string”

echo $b # prints “this is a string”

Read statement • stores console input into variables (different from

positional arguments)

• ex:

#!/bin/sh

# read example

echo ‘what is your name?’

read name

echo ‘Well’, $name, “you typed “ $# “arguments”

echo “and they are:” $*

The expr Utility

• syntax : expr arg1 <op> arg2

<op> can be:

• +, -, \*, / (int division), % (int remainder)

• meaning: evaluates the expression

• ex: expr 3 + 4 7 (note space around +)

expr 3 / 4 0

expr 3 % 4 3

• Shell script can be written for simple arithmetic

operations.

• #!/bin/sh

# add two numbers

sum=`expr $1 + $2`

echo “result is: “ $sum

$ add 3 4

result is: 7

$ add 4.9 4.3

----error (integer value expected)

if-then statement • Syntax

if cond

commands

• #!/bin/sh

set `date`

if test $1 = Fri

echo “Wula, weekend”

test command compares values and checks

file types, and sets the (internal) exit status

depending on result

Arguments of test

command

-d file file is a directory

-f file file is a file

-r file file is readable

-s file file size > 0

-x file file is executable

-w file file is writable

! -d file file is not a directory

! -f file file is not a file

! -r file file is not readable

! -s file file size not > 0

! -x file file is not executable

! -w file file is not writable

n1 –eq n2 n1 = n2

n1 –ge n2 n1 >= n2

n1 –gt n2 n1 > n2

n1 –ne n2 n1 \= n2

n1 –lt n2 n1 < n2

n1 –le n2 n1 <= n2

n1, n2 are integers

s1 = s2 s1 equals s2

s1 != s2 s1 is not equal to s2

s1, s2 are strings

If-then-else

• syntax

• if cond

commands

• #!/bin/sh

# if example

set `date`

if test $1 = Fri

echo “Wula, weekend”

echo “still have to work”

Remove files

#!/bin/sh

# file del

# delete files interactively

if test ! –f $1

echo “no such file” $1

echo “do you want to delete” $1 “(y/n)”

read choice

if test $choice = y

echo $1 removed

echo $1 “not removed”

Case statement • Syntax

case var in

p1) comd1; …; comdn ;;

p2) comd1;…; comdn;;

pn) comd1;…; comdn ;;

*) comd1; …; comdn ;;

ex: • #!/bin/sh

# case ex

• set `date`

• case $1 in

• Fri) echo "Friday";;

• Sat | Sun) echo "weekend too";

• echo "go fishing";;

• *) echo "not weekend";

• echo "need to work";;

• esac

For-loops

• Syntax

for var in list

commands

• #!/bin/sh

for name in $*

finger $name

echo *********

#!/bin/sh

b="1 2 3 4 5 6 7 8 9 10"

for a in $b

echo "value is" $a

#!/bin/sh

# an improved spelling script

for word in `spell $1`

line=`grep -n $word $1`

echo " "

echo "misspelled word: $word"

echo "$line"

grep –n word file

find and print each

line in file that contains

While-loops

• Syntax

while cond

commands

• #!/bin/sh

while test $c –gt 0

echo value: $c

c=`expr $c – 1`

shift command • shifts positional parameters ($1,$2,…) one

position to the right over the arguments

• $0 is not shifted

• ex: % mycomm 1 2 3 er ds

$0 $1 $2 $3 $4 $5

% mycomm 1 2 3 er ds

$0 $1 $2 $3 $4

part of a

shell script

Overview

The simplest “hello, world” program

# include <stdio.h>

main()

printf("Hello, World\n");

How to compile and execute C

programs? (gcc can be replaced by cc)

$ gcc test.c

$ a.out

Or $ gcc –o name test.c

$ name

Understanding the program

# include <stdio.h>

main()

printf("Hello World\n");

#-line: preprocessing directives.

Cause pre-processor to include the

header file stdio.h which contains info

about printf()

The function main()

where execution begins

Print the string “Hello Word”

on the screen (and advance to

the next line), by the function

printf()

As a variation, what would be the

output?

# include <stdio.h>

main()

printf("Hello\nWorld”);

Basic Input and Output

Input:

• syntax:

• scanf(control string, other-args);

• ex:

• scanf("%d%d", &x, &y);

• semantics: read and convert two inputs from

the input stream into variables x and y in the

format specified in the control string

scanf()

Format

(conversion

To what?

c a character

d a decimal integer

f a floating point number (float)

lf a floating point number (double)

s a string

Basic Input and Output

output:

• syntax: (formatted print)

• printf(control string, other-args);

• ex:

• printf("%3c%5c\n", ‘A’, ‘C’);

• semantics: print out characters A and C in the

format specified in the control string

• _ _ A _ _ _ _ C

printf()

Format

(conversion

how to print the arguments?

c as a character

d as a decimal integer

f as a floating point number

e as a floating point number in scientific notation

s as a string

for more info: search online C manual/tutorial

width and

precision

positions taken by

precision is included in

- will left-justify,

the default is

right-justify

Fundamental Data Types

(long)

double

(long double)

(boolean? String?)

no boolean type

• 0 is “false”,

anything else is

“true”

no string type

• string is char array

• ex: char s[10];

Identifiers

rule: {letter | _ }1{letter | _ |digit}0+

ex: a, _a, month_of_year

but not

not#me

declaration of variables

syntax:

type var1, …, varn;

ex: int x, y;

double x1;

int x, y=3;

declaration and

initialization done in

“one step”

Basic operations/operators

+ (unary) - (unary) ++ --

+ (binary) - (binary)

= += -= *= /=

(Q: should negative symbol and subtraction

symbol be distinguished in math?)

Assignment statement

Java is the same as C

Syntax

• <var> = expression;

ex: a = 3;

x = x + 1;

etc…

C is not “type safe”

compiler will not

complain, but you

will see a run-time

error.

++ and --

increment / decrement operator

++a and a++ are different

When a++ or ++a are not alone, the

effect of the difference will be shown

• First all of, the expression a++ or ++a will be

evaluated (to yield a value)

• then, the yield value (i.e. evaluation result) will

be used in the surrounding context (since a++

or ++a are not “alone”)

so, ++a causes a to be increased by 1

first, and the value of the expression ++a

is whatever stored in a.

a++, the value of the expression a++ is

the current value of a. Then a is

incremented by 1 after (the evaluation of

this expression)

use ++ or -- with caution (or, don’t use it)

Quick test using Java

interaction tab

the expression a++ is

being evaluated, and

the result is 1

the expression ++a is

being evaluated, and

the result is 2

A quick question: what is the

difference between a=1 and

a=1; in Java (and C)?

sizeof () operator

gives the size (in byte) required in

memory for fundamental types

ex: (next slide)

more about assignment

= is an operator in C, and has the

associated value

compare + (as in a + b) with

= (as in a = b)

a + b is an expression, so is a = b

a + b has a value, so does a = b

a + (b + c) makes sense,

so does c = (a = b)

but , this style of programming, is not

suggested.

And, Java follows it

a=b is an expression (and thus will be

evaluated to a value)

a=b; is not an expression (and will not

be evaluated to a value)

this example

should drive the

point to home

char and int (C is not strongly

typed)

character can be considered as int

and vice versa (see next slide)

note: not saying int is the same type as

char (4 bytes vs 1 byte). We cannot

declare a variable as type int and char at

the same time

again, this style of programming is not

suggested (it is allowed of course)

Relational , equality, and logical

operators

same meaning as in Java

false = any zero-value

(0, 0.0, or NULL, …)

true = any non-zero value

Consider this….

There is no logical type (boolean type) in

But, there are logical operators in C (!,

&&, ||)

So, what is the response to the following

expression in C (and Java)?

3 < j < 5 when j =7

3 < j < 5 is the same as (3 < j) < 5

3 < j yields 1 (true), when j=7. so

(3 < j) < 5 is the same as

1 < 5,

which yields 1 (true)

lesson learned: typing is important (so

boolean type is needed)

true in C

false in C

“strange” things ...

In Java, it’s a different story…,

due to STRONG typing in Java

More about what typing can

cause ...

while/if (a = 1)

………… /* do sth */

while/if (a == 1)

….. /* do sth */

both are syntactically correct in C

the first one will run forever, and thus

cause a perplex...

the second one is what we want..

Java won’t compile something

like this

this shows typing is

important !!!

Selections

if-statement

syntax

• if (expression)

statements

if ( a == 1)

x = y;

if-else statement

syntax

• if (expression)

statements

• if ( x == y)

i =1; j =2;

{ i = j;

ex: is the following code syntactically

correct? if not, what is wrong?

if (i == j)

{ i = i+1;

j = j+2;

i = j-1;

which “if” does the “else” go w/?

ex: is the following code

semantically clear?

if (i == j)

if (a == 2)

i = i+1;

j = j-1;

if (i == j)

if (a == 2)

i = i+1;

j = j-1;

rule : the else matches with nearest if.

So the left one is will be “chosen”.

but, what if we intend to do the other

what if we want to do the “right”

ex: is the following code

semantically clear?

if (i == j)

if (a == 2)

i = i+1;

j = j-1;

if (i == j)

{ if (a == 2)

i = i+1;

{ j = j-1;

Is this else-if statement?

if (….)

printf(…);

else if (…)

printf(….);

while-loop

syntax:

• while (expression)

statements

usage:

the same as Java (Java follows C)

for-loop

same as Java

syntax:

• for (expr1; expr2; expr3)

statements

next statement

meaning interpreted in terms of while-

expr1;

while (expr2)

statements;

expr3;

next statement

the conditional operator ?:

?: is ternary

syntax:

expr1 ? expr2 : expr3

if expr1 is true, then expr2 will be the result

of the entire expression, otherwise expr3

will be the result of the expression.

what is going on in Java?

It will be evaluated … But, what

would be the type of evaluation

result?

what would be the type

of the expression????

functions (modular

programming)

#include <….>

function prototypes (optional )

function defs

main ()

{…..}

functions

recursive functions

Pointers, 1-d Arrays, Strings

Pointers

• variables holding memory addresses

1-d arrays

• vectors (same as Java)

• index starts from 0 (not 1)

Strings

• 1-d array of characters

• last value of a string is ‘\0’

example of strings

• “abcde” is stored as

‘a’ ‘b’ ‘c’ ‘d’ ‘e’ ‘\0’

pointer declaration:

• ex: int *p;

• meaning: p is a pointer to type int; or p is a

variable of type int *; or p refers to some

memory location which holds an int value; or

*p is of type int.

(NULL)

if p is a pointer, then *p (called pointer

dereferencing) means the memory

location (cell) which is pointed by p.

int q=1, *p;

p = &q;

int *p;

can be understood in both ways:

• as (int *) p; i.e., p is variable of type int *.

• as int (*p); i.e., *p is a variable of type int.

Example

next slide, study it carefully, as it

involves some fundamental facts about

pointers.

Now, why doesn't it work?

same thing as before …

(changing

p to &p) is

not the

problem.

supposed

to be p (a

pointer).

to fix it:

type synonym : typedef

give a new name for existing types:

• typedef char * string;

• typedef int number;

• string s1;

• number n;

structure (or record)

syntax

• struct name

type field;

name is optional

after this, struct complex (together) is

used as a type

accessing members of a structure

• use the “.” operator

structure_var . member

or use the “->” operator

ptr_to_structure -> member

or, equivalently

or, (maybe better)

or, w/ pointers

or, w/ header file

Put definition (and other things) of type

complex is in a header file, say,

complex.h.

then, to have better moularity

Use structure w/ functions

HTML Basics

HTML – Hypertext Markup Language

Background

• Who: Tim Berners-Lee

• Where: CERN, Swiss

• When: 1989

• http://public.web.cern.ch/Public/Welcome.html

Used to write WWW (web) pages

Structure of a HTML document • <html>

<body>

…………….

…………..

</body>

</html>

• Note:

• A html file is a plain text file

• <..> -- opening tag

• </..> -- closing tag

• Opening tags are paired with corresponding

closing tags (not so strict)

• Place the html file in the public_html directory on

eclipse

• an example (next page)

Type styles • Tags to typeset documents

• Heading style • <H1> largest and boldest

• <H2>

• …

• <H6>

• <cite> -- citation

• <em> -- emphasis

Down in size

• <strong> -- bold

• <code>, <kbd> -- monospaced font

• <address> -- italic, email, phone #, address

• <big> -- big font

• <small> -- small font

• <sup> -- superscript

• <sub> -- subscript

Ex: <H1> Look Here </H1>

Look Here

B<sup>2</sup>

Horizontal alignment of text

• Syntax:

• <p> makes a paragraph

• <p align = x > …..</p>

x = left, right, center

• <center> ……….</center> (will center and make

a paragraph)

• Ex: <p align=right> this line </p>

Comments (which one, confusing) •

• <! …… >

• Def: • Comment declaration: <! … >

• Comment contents: start with -- end with -- contain no occurrence of –

• A comment is: comment declaration which contains zero or more comment contents

• So <!>,  are all legal comments

• But  is not

• Unfortunately, not many browsers coded to recognize it.

Font sizes

• Syntax: <font size=x> … </font>

• x can be 1,2,…, 7

• From small to large

• Default size = 3

• Ex: <font size=5> large font </font>

Fixed type styles • Unlike relative style tags (e.g. <h1>), fixed type styles do

not vary from one browser to another.

• style tag

bold <b> </b>

italic <i> </i>

underscore <u> </u>

typewriter <tt> </tt>

strikeout <s> </s>

Line and paragraph breaks

• <br> ends a line w/o adding any space

• <p> ends a line and adds a line space

• <nobr> </nobr>

prevents texts and graphics from

breaking and reflowing

Text links

• <a href=“…...... “> …….…</a>

anchor

Hypertext ref name of link

text to click

• <a href=“art.html”>click here</a>

• <a href=“lab1.txt”>click here</a>

• <a href=“http://www.nicholls.edu”>click here</a>

• <a href=“mailto:cmps-cx@nicholls.edu"”>click here to mail

me</a>

Graphics

• <img align=x src=“….” width=“..” height=“…”>

• ex: <img src=“clips.gif”>

optional name of pic

x= top, bottom, middle

• Border on graphics

• <img src=“……” border=“…”>

• Graphic links

• <a href=“…..”> <img src=“…..”> </a>

pixels

Name of

resource picture

Background color, text color, and link color • <body bgcolor=“#302030” text=“#246050”

link=“#505050”>

• https://html-color.codes/

• color name(“red”), hex-code (“#ffffff”), rgb-code(“(0,34,0)”)

• List • unordered list

• <ul type=x> x = circle or square w/wo “”

<li> …

<li> ….

optional

• Ordered list • <ol type=x> x=1,A,a,i

<li> ….

<li> …..

Dividing rules • <hr>

• <hr size=“…” width=“…” align=x>

x= left, right, center

height length

Links within documents

• <a href=“#....”> …. </a>

• <a name=“…”>….</a>

• Ex: <a href=“#comp”>computer</a>

<a name=“comp”> computer def </a>

text same

Block quote • <blockquote>

</blockquote>

Background (design) • <body background=“…..”>

Preformatted text • <pre>

………….

</pre>

indented

Graphics file

Exact appearance

Example

• Using what we have covered so far, we can

compose the following webpage. (next slide)

Table • <table border>

</ table>

Top or bottom caption

row Heading cell

Table data

Optional (show or not show border)

Borders, spacing, padding

• <table

border=10

cellspacing=6

cellpadding=10>

Width of frame

Space between 2 cells

Space between text in a cell

and cell gridline

Alignment

• Put align=x (x=left, center, right) in

• Ex: <tr align=center>….. </tr>

whole row is centered

only this cell is aligned to left

Width control

• <table width=400>

specifies the width of the table

• <th width=50>

specifies the width of the cell

Spanning rows and/or columns

• <th rowspan=2> …..</th>

• <th colspan=2> …..</th>

• <td rowspan=2> …..</td>

• <td colspan=2> …..</td>

The <form> element • <form action=“…” method=“…”>

put form elements here

</form>

Input texts into forms • Using the <input> element: Generate various

ways for users to enter info into forms • <input …..some attributes…… >

• Common attributes: type, name, value

• Using the <textarea> element: allows a

paragraph of texts to be entered

• <textarea …some attributes….. >

some default text

</textarea>

Input selections

• Checkbox

• <input type=“checkbox” name=…. value=...>

• Radio button

• <input type=“radio” name=… value=...>

• Drop-down list

• <select name=…size=…>

• </select>

# of lines visible

Submitting and clearing forms

• <input type=“submit”>

• <input type=“reset”>

Generate a submit button and a reset button

respectively

Form Processing -- CGI

CGI programs– Common Gateway Interface

programs. They are used to process forms

CGI programs can be written in any language

supported by the Web server, e.g., C, C++,

Java, Perl.

CGI programs are installed on server and

specified by the action attribute of the form tag.

• <FORM METHOD="POST"

ACTION="http://web.mit.edu/bin/cgiecho/wwwdev

/cgiemail/questions3.txt">

• <FORM METHOD=“get" ACTION=“./cgi-bin/test.pl”>

• “get” appends data from form to the end of URL in the

resulting window; “post” does not do so and merely

send form data to the Web server to be processed.

MIT cgiemail program

Free CGI program for Unix

Easy to use

http://web.mit.edu/wwwdev/cgiemail/

It collects data from a form and sends

them to a specified email address in a

specified format

Steps to make cgiemail work on

our Unix

Go to cgiemail website, download binaries cgiecho and cgiemail to your cgi-bin directory, say, /home/xing/public_html/cgi-bin.

Rename them as cgiecho.cgi and cgiemail.cgi

Change file mode of these two files (chmod 755 ….)

Create an email template (an ASCII file) which specifies the format of the email which will be sent to you (or someone else) by the web server.

Here is an example of the email template

From: [email]

To: cmps-cx@nicholls.edu

Subject: questions three

What is your name? [yourname]

What is your quest? [quest]

What is your favourite colour? [colour]

This allows the form data to be sent to cmps-

cx@nicholls.edu w/ sender being identified as [email]

Put this file (say file name is quest3.txt) into your public_html directory,e.g., /home/xing/public_html

Test this file with your browser to make sure it is readable.

Create a html form in your public_html directory,say, /home/xing/public_html

An example of the html file is as follows: note that the values of the name attributes MUST be the same as that in the email template

<html>

<body>

<FORM METHOD="get"

ACTION="http://eclipse.nicholls.edu/~xing/cgi-bin/cgiecho.cgi/~xing/quest3.txt">

Your e-mail address: <INPUT NAME="email"><p>

Your name: <INPUT NAME="yourname"><p>

Your quest: <INPUT NAME="quest"><p>

Your favourite colour: <INPUT NAME="colour"><p>

</FORM>

</body>

</html>

Set the value of action of the form tag to be:

ACTION=http://eclipse.nicholls.edu/~xing/cgi-bin/cgiecho.cgi/~xing/quest3.txt to echo the form data (no email will be sent) or

ACTION=http://eclipse.nicholls.edu/~xing/cgi-bin/cgiemail.cgi/~xing/quest3.txt to send form data as an email

Save the file in your public_html directory, say, /home/xing/public_html/myform.html

Open myform.html using your favorite browser

The email template

The html form file

Executing the html form file

Click it

Response from clicking the

button

What is in my mail box

Overview

SGML • Standard Generalized Markup Language

• Widely used for large-scale documentation project (IRS, DoD, Health care…)

• 1986

HTML • Hyper Text Markup Language

• First language for WWW

• Early 1990

• Limitations (for example)

• Loose syntax, (“” or no “”, close tag or not?,

lowercase or capital?...)

• web browser forgiving, but not new wireless

devices (cell phone, PDA, car navigator…)

• Can’t be extended

XML • Extensible Markup Language

• 1998, by W3C (WorldWideWeb Consortium)

• Motivated by the limitations of HTML

• Combination of XML and HTML

• 2000, XHTML 1.0

Converting HTML to XHTML

All mark elements must be lowercase • Ex: HTML: <TITLE> … </TITLE>

XHTML: <title> … </title>

Every open tag must correspond to a close tag • Ex: HTML: <ol>

<li> item1

<li> item2

XHTML: <ol>

Empty-element syntax • Ex: HTML: <BR>

XHML: <br />

Every attribute must have a value. The value needs to be surrounded by single or double quote marks • Ex: HTML: <input type=button checked>

XHTML: <input type=“button” checked=“checked” />

Proper nesting of elements is required • Ex: HTML: <p><em>…</p></em>

XHTML: <p><em> … </em></p>

All XHTML documents must contain DOCTYPE declaration and may, optionally, contain an XML declaration • <?xml version="1.0" encoding="UTF-8"?>

• <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

• "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

The root element <html> must contain

an XHTML namespace

• <html xmlns="http://www.w3.org/1999/xhtml">

Three types of DTD (Document

Type Definition)

Transitional

Frameset

Strict

Replace any by another in DOCTYPE

declaration

example

Validation of XHTML documents

Go to http://validator.w3.org

Submit your document

Example: submitting the previous

sample xhtml document

Introduction to

JavaScript

Background

In early 1990, “www” so “hot” that everyone was talking about “.com”

In 1995, Netscape (Brendan Eich) decided to script the HTML, the scripting language was called LiveScript

Netscape and Sun worked together to implement the scripting language into Netscape Navigator 2.0. The name changed from LiveScript to JavaScript (for marketing purpose)

Microsoft followed this idea, released Jscript the next year

JavaScript vs. Java

JavaScript ≠ Java

JavaScript : loosely typed

Java: strongly typed.

JavaScript: tied w/ web programming

Java: general purpose

Basic Structure

…..<head> ……

js code here

</script>

…………..

</head>

<body>

…………

js code here

</script>

………..

</body>

The <script>…</script>

can be inserted at

different places

…..<head> ……

js code

</script>

…………..

</head>

<body>

…………

js code

</script>

………..

</body>

JS Syntax and Semantics

Similar to that of Java (skip)

• for (i=0; i<10; i++)… for-loop

• while (i < 10)… while-loop

• var a; variable declaration

• a =1; assignment statement

• if (a <=b)… branching

example: loop

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<head>

var i;

for (i=1;i<=10;i++)

document.write("do it"+i+"time <br />");

document.write("<h1> stop the loop! </h1>");

</script>

</head>

<body>

src="valid-xhtml10.gif"

alt="Valid XHTML 1.0 Transitional" height="31" width="88" /></a>

</body>

</html>

Or, put the js into another file

<head>

</script>

</head>

<body>

</body>

</html>

path of the file x.js

example: loop

// the x.js file

var i;

for (i=1;i<=10;i++)

document.write("do it"+i+"time <br />");

document.write("<h1> stop the loop! </h1>");

It will do the same thing

example: branching

<head>

var answer = window.prompt("who are you? Type your name here", "???");

if (answer == "John")

window.alert("Hello, John");

window.alert("fatal error! memeory dump! Shut down the system!");

</script>

</head>

<body>

</body>

</html>

example: branching

example: function (rewriting of

previous example)

<head>

function doIt(x)

if (x == "John")

window.alert("Hello, John");

window.alert("fatal error! memeory dump! Shut down the system!");

</script>

</head>

<body>

var answer = window.prompt("who are you? Type your name here", "???");

doIt(answer);

</script>

<!– the logo here -->

</body>

</html>

Browsers load (x)html codes, from top to

bottom, into memory

Common practice: put functions inside

<head></head> element so that the

browser “knows” the functions before

they are invoked.

Check Boxes

Purpose: make multiple (one or more)

choices

How to make checkboxes?

How to check which boxes are checked?

Ex: (2 approaches, both fine)

function showIt(f)

f.result.value=""; // reset the result value

if (f.food0.checked)

{ f.result.value="steak"; }

{ f.result.value=f.result.value+",seafood"; }

{ f.result.value=f.result.value+",vege"; }

</script>

Select the ones you like: (all that apply) <br />

<input type="checkbox" name="food0" /> steak <br />

<input type="checkbox" name="food1" /> seafood <br />

</form>

function showIt(f)

f.result.value=""; // reset the result value

if (f.food[0].checked)

{ f.result.value=f.result.value+",seafood"; }

{ f.result.value=f.result.value+",vege"; }

</script>

Select the ones you like: (all that apply) <br />

<input type="checkbox" name="food" /> steak <br />

<input type="checkbox" name="food" /> seafood <br />

</form>

Radio Buttons

Purpose: you can only choose ONE

choice, not allowed to choose more than

How to create radio buttons?

How to check which button is selected?

Ex: make a choice and show what

choice is made.

function showIt(f)

{ f.result.value="seafood"; }

{if (f.food[2].checked)

{ f.result.value="vege"; }

{f.result.value="nothing is chosen";}

Make your choice: <br />

<input type="radio" name="food" /> steak <br />

<input type="radio" name="food" /> seafood <br />

</form>

a better treatment might be the following:

function showIt(f)

var i;

for (i =0; i<3; i++)

if (f.food[i].checked)

{ f.result.value=f.food[i].value;

break;

Or the following:

function showIt(f)

alert("# of elements="+f.elements.length);

var i;

for (i =0; i<3; i++)

if (f.elements[i].checked)

{ f.result.value=f.elements[i].value;

break;

Make your choice: <br />

<input type="radio" name="food" value="steak" /> steak <br />

<input type="radio" name="food" value="seafood" /> seafood <br />

</form>

You will see the same result

onmouseout

onmouseover

Swap to “3l” image every 3 seconds

Swaps to “logo” image every 3 seconds

Lab25 (last one)

Find two of your favorite pictures and

swap them every 2 second.

Print the screen shots and XHTML code

Problems w/ eclipse?

Unix, C Programming, and (X)HTML · 2019. 10. 24. · Unix-like systems: systems that work much...

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