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Unix and C Programming
Dr. Cong Xing
Dept. of Math & CMPS
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 =
pulse per second. 3 Ghz = 3 billion pulse per
second.
1
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 space (in
terms of bytes) can a 32-bit CPU memory
address?
232 = 22 210 210 210 = 4GB
32-bit long register
• Flops: short for floating point operations per
second. Also used to measure the speed of
computers.
The origin of Unix
• 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
=140
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.
utilities
shell
user
File sys
kernel
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)
BSD Unix: modified at Berkeley and as
popular as AT&T Unix. (MacOS X is based on
BSD Unix)
•
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
•
•
•
A GUI for Unix, developed at MIT
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
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.
Young
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)
Getting Started
Use putty ssn or telent to login to eclipse
Successful login shows:
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
Shell prompt
•
•
•
$ -- Bourne shell, Korn shell, or bash shell
% -- C shell or TC shell
Will use $ throughout the slides
Script session
•
•
$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
Spelling
• $ logout or
• $ exit or
• $ ^D
• One of the above has to work
• 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,….)
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:
Root (/)
bin
dev
etc
home
tmp
Users’ home directories
usr
var
• 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
root /
home
smith
al
cmps
hw1
math
hw2
• ~ (tilde) represents the absolute pathname of
•
your home directory
~<username> represents the absolute
pathname of the home directory of that user
Relative pathnames
• relative to working directory
• . -- the current working directory
• .. -- parent of current working directory
• 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 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-
•
node.
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
name1
name2
name3
name4
Long Listing
• More info about files can be shown by
$ ls –l
drwxr-xr-x 2 xing staff
-rw-r--r-- 1 xing staff
drwxr-xr-x 2 xing staff
512 Jan 23 11:40 t
8 Apr 26 2004 test
512 Aug 24 00:06 test1
drwxr-xr-x 2 xing
File
links
type
Access
control
owner
staff
512 Jan 23 11:40
test
group
Size
name
(byte)
Date &
time
• 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
• 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
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
rwxr--r-rw-rw------------
= 777
= 744
= 660
= 000
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
6
2
3
2
1
2
=3𝑟0
=1𝑟1
=0𝑟1
610 = 1102
6
14
=7𝑟0
2
7
=3𝑟1
2
3
=1𝑟1
2
1
=0𝑟1
2
610 = 11102
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 and
$ page fname
-- similar to more
Concatenating Files
• $ cat
•
file1 file2 ….
-- display 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
$ ls
Removing a directory
Changing working directory
• $ rmdir dn --- remove the dir dn
• $ cd dn
--- switch to dir dn
Returning to the home directory
Printing your working directory path
• $ cd or
• $ cd ~
• $ pwd
Unix common shells
name
what
when
where
who
Bourne shell
(sh)
Original
shell
1979
AT&T
Steven Bourne
Korn shell
(ksh)
Improved
sh
1986
AT&T
David Korn
Bourne again
shell (bash)
Improved
sh
1988
GNU project Brian Fox, Chet Ramey
C shell (csh)
BSD Unix
1979
UC Berkely
Bill Joy
TC shell (tcsh)
Improved
csh
1980
CMU, Ohio
State
Ken Greer, Paul
Placeway
Debian
Almquist shell
(dash)
Decendant 1977
Almquist
(2002
Shell (ash) rename)
BSD
Kenneth Almquist
Your login shell
• Shown at the command line prompt
• (check what is your login shell, $ ps)
• Or, read contents of /etc/passwd
• Ex: $ grep cxing /etc/passwd
• Or,
$ echo $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)
How Shell Processes Commands
Shell displays
prompt (e.g. $) –
ready to receive
commands
shell interprets
the command
(looking for prog)
User types
A command
Kernel runs the
program and shell
“goes to sleep”
User types
return (end
of command)
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 where programs send
output. (monitor by default)
standard error: the file where 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
$w
$ ls
$ cal
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
Tees
tee file -- copies stdin to stdout, making a copy in file
stdout
file
stdin
What entered
(stdin)
(response to input
: stdout ^d to
finish)
outfile
command2
command1
$ 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
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
Ex:
• $ 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
To bring it to Nothing
foreground
To send it to Suspend it
background and bg it
To Terminate ^c or
^z then kill it
To suspend ^z
Suspended
process
Fg it
Bg running
process
Fg it
Bg it
Nothing
Kill (-9) it
Kill (-9) it
Nothing
Stop it
History and filename completion
• $ history
• $ !#
• $ !!
• Trick
lists recently typed commands
To re-run a command, # is the
number
to re-run last command
• Under csh, tcsh, bash, filenames can automatically
be completed by hitting the tab key
To check your login shell
•
•
•
ps
or
echo $SHELL
echo $shell
or
To leave a shell
•
$ exit
or $ logout
ftp and telnet (or ssh)
•
built-in Unix utilities
•
$ telnet hostname
• telnet (or ssh): remote login to a networked computer
• ftp (sftp): file transfer protocol
• $ ftp (sftp) [-port] 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 WS_FTP32, WinSCP
• open My Computer | type hostname in the address
bar
• open a web browser, type the hostname in the
URL bar
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 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
Text Editor – Vi (or Vim)
To invoke vi
• $ vi fname
Unix shell
vi fname
:x
Comm mode
i, o
esc
Insert mode
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”, “k”,.... ? --Nearby finger tips
Left index
finger
right index
finger
• x ---- delete one character
• dd --- delete entire 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 two lines together
:w fname --- save file to fname
•
“copy & paste” – yank and put
•
(do the following in command mode)
• ma (at the beginning of block)
• y'a (at the end of block)
• p (put what being yanked)
Spell checking
Search
• $ spell fname
• $ ispell fname
• / pattern --- find occurrence of pattern
• / <return> --- repeat last find
• ? pattern --- works like /, but backwords
• ? <return> --- works like /, but backwords
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
• %
• $
• ex:
•
bindkey –v
set –o vi
(tcsh shell)
(bash )
$ 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
Network
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
bus
ring
star
hub
Internet History
Internet Protocols
• (see http://en.wikipedia.org/wiki/Internet)
• Protocols --- data communication rules
• TCP – Transmission Control Protocol
High speed
• IP – Internet Protocol
• PPP --- point-to-point protocol
Low speed
• SLIP – serial line internet protocol
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
•
name
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
• cn – China
ch -- Switzerland
fr -- France
E-mail (built-in in Unix)
Check to see if one has read his mail
• mail – original
• Mail – Berkeley mail
• mailx – System V mail
• elm – alternative to standard Unix mailers
• pine – similar to elm
• finger userid
•
ex: finger xing
(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
Common Mail Conventions
•
•
•
:-) -- smile
;-) -- wink
:-( -- frown
Classic Unix Network Utilities
•
•
•
•
rlogin -- remote login
telnet – remote login
ftp – file transfer
rcp -- remote copy
Basic ftp commands
•
•
•
? -- 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 at the end of each line
when display in Unix.
How to fix it? Type the following
• tr –d ‘\015’ < inputFile > outFile
Octal for ^M
Output file name
Input file name
• 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
• http://www.neurophys.wisc.edu/comp/docs/ascii/ to
check binaries, octals, etc…
• http://www.unix-manuals.com/refs/misc/asciitable.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
request
client
server
answer
• URL (Uniform Resource Locator)
•
•
http://www.nicholls.edu
ftp://eclipse.nicholls.edu (what does the header “http” or
“ftp” mean?)
• 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
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)
•
list contents of the archive
• $ tar –tf fn.tar
• $ tar –xf fn.tar
• restores the archived directory
Computer Security
Cryptography
• Plaintext: original unencrypted text.
• Ciphertext: encrypted text.
• Algorithm: transform plaintext into ciphertext
•
(and vice versa).
Key: info, such as a word, a phrase, required
to encrypt or decrypt a message.
How to send the
secret key over
the Internet?
Encryption scenarios
•
•
•
Secret-key encryption: use the same key to encrypt
and decrypt a message
Public-key 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 authentication: message/request is
encrypted using private key (by the sender) and is
decrypted using the public key (by the receivers).
(Typical situation when login to a server)
Here we go!
key
sender
alg
/R&
A
ciphertext
plaintext
key
receiver
A
plaintext
Internet
alg
/R&
ciphertext
secret-key encryption
public key
sender
alg
/R&
A
ciphertext
plaintext
private key
receiver
A
alg
Internet
/R&
ciphertext
plaintext
public-key encryption
private key
sender
alg
/R&
A
ciphertext
plaintext
public key
receiver(s)
A
plaintext
Internet
alg
/R&
ciphertext
public-key authentication
RSA RSA RSA
RSA
•
•
•
•
•
•
•
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
•
% ssh user-name@host-name
• eady to go:
• 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 gow 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
Check
here
Click
here to
locate pk
Click here
(or, newer)
(or, newer)
WULA!!!
WULA!!!!
I can relax now.
(or, newer)
WULA!!!!
Again!.
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.
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
•
•
•
•
Scripting html document: JavaScript, Netscape
Web browser (graphical and nongraphical): Netscape
(Mosaic)
Security, RSA: obvious
Computer fundamental layout: John von Neumann
• http://www.cern.ch
• 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 shell
TERM
Your terminal type
MAIL
Pathname of system mail
USER
Your user name
Setting Environment Variables
• depends on shell
• sh, ksh, bash
• ex:
TERM=vt100
• csh, tcsh
• ex: setenv TERM vt100
Listing Values of Environment Vars
• sh, ksh, bash
• set
•
• setenv
Check the value of a specific Environment
Variable
•
csh, tcsh
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
•
% set
To set value of special variable
•
% 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 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
cal
date
w
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,…)
•%
• or
sh shs (or % csh shs)
• % chmod u+x shs
• % shs (or ./shs)
(mark shs executable)
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
cal
date
w
• 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
•
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, $1 holds the first argument, S2
the second argument, $3 the third argument, …
ex:
#!/bin/sh
# a shell script, name: shs0
cal
date
w
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 makes a file execute.
#!/bin/sh
# make a file executable
chmod u+x $1
echo $1 ‘is now executable’
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
date produces
Fri Aug 20 10:33:34 EST 2005
which is caught by set and consequently assigned
to
$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: $3”
User-defined variables
•
•
•
combination of lower case letters, upper case letters,
underscore, and digits.
first character cannot be digits
ex: a, b1,c2, f_var
Assignment
•
•
<var>=<value> (no space in between)
Ex: a=“this is a string”
b=$a
echo $b # prints “this is a string”
Read statement
•
stores command line arguments 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 statement
•
Syntax
if cond
then
commands
fi
ex:
•
#!/bin/sh
set `date`
if test $1 = Fri
then
echo “Wula, weekend”
fi
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
s1 = s2
s1 equals s2
n1 –ge n2
n1 >= n2
s1 != s2
s1 is not equal to s2
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 are strings
If-then-else
•
syntax
•
if cond
then
commands
else
commands
fi
ex:
•
#!/bin/sh
# if example
set `date`
if test $1 = Fri
then
echo “Wula, weekend”
else
echo “still have to work”
fi
Remove files
if test $choice = y
then
rm $1
echo $1 removed
else
echo $1 “not removed”
fi
#!/bin/sh
# file del
# delete files interactively
if test ! –f $1
then
echo “no such file” $1
else
echo “do you want to delete” $1 “(y/n)”
read choice
fi
Case statement
•
Syntax
case var in
p1) comd1; …; comdn ;;
p2) comd1;…; comdn;;
…..
pn) comd1;…; comdn ;;
*) comd1; …; comdn ;;
esac
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
do
commands
done
Ex
•
#!/bin/sh
for name in $*
do
finger $name
echo *********
done
Ex:
#!/bin/sh
b="1 2 3 4 5 6 7 8 9 10"
for a in $b
do
echo "value is" $a
done
Ex:
#!/bin/sh
# an improved spelling script
for word in `spell $1`
do
line=`grep -n $word $1`
echo " "
echo "misspelled word: $word"
echo "$line"
done
grep –n word file
find and print each
line in file that contains
word
While-loops
•
Syntax
while cond
do
commands
done
Ex:
•
#!/bin/sh
c=10
while test $c –gt 0
do
echo value: $c
c=`expr $c – 1`
done
shift command
• shifts positional parameters ($1,$2,…) one
•
•
position to the right
$0 is not shifted
ex: % mycomm 1 2 3
$0
$1 $2 $3
shift
% mycomm 1 2 3
$0
$1 $2
er ds
$4 $5
er ds
$3 $4
C
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
#-line: preprocessing directives.
Cause pre-processor to include the
header file stdio.h which contains info
about printf()
# include <stdio.h>
main()
{
printf("Hello World\n");
}
The function main()
where execution begins
Print the string “Hello Word”
on the screen (and advance to
the next line), by the function
printf()
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
char)
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:
•
• 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
char)
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
Fundamental Data Types
int
(long)
float
double
(long double)
char
(boolean? String?)
Identifiers
rule: {letter | _ }1{letter | _ |digit}0+
ex: a, _a, month_of_year
but not
not#me
101_n
-plus
declaration of variables
syntax:
type var1, …, varn;
ex: int x, y;
double x1;
int x, y=3;
Basic operations/operators
()
+ (unary) - (unary) ++ -* / %
+ (binary) - (binary)
= += -= *= /=
Assignment statement
Java is the same as C
ex: a = 3;
x = x + 1;
etc…
++ and -increment / decrement operator
++a and a -- different
ex:
so, ++a causes a to be increased by 1
first, and the value of ++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.
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 + in a + b, with
= in a = b
a + b is an expression, so is a = b
a + b has a value, so is a = b
(a + b) + c makes sense,
so is c = (a = b)
but , this style of programming, not
suggested.
ex:
char and int
character can be considered as int
and vice versa
note: not saying int is the same type as
char. We cannot declare a variable as
type int and char at the same time
again, this style of programming is not
suggested (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
ex:
Consider this….
There is no logical type (boolean type) in
C
But, there logical operators in C (!, && ||)
So, what about the following expression
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
more about what typing can
cuase
if (a = 1)
………… /* do sth */
if (a == 1)
…..
/* do sth */
both are syntactically correct
the first one will run forever….
the second one is what we want..
Selections
if-statement
syntax
• if (expression)
statement
ex:
if ( a == 1)
x = y;
if-else statement
syntax
• if (expression)
statement
else
statement
ex:
• if ( x == y)
{
i =1; j =2;
}
else
{ i = j;
}
ex: is the following code syntactically
correct?
if (i == j)
{ i = i+1;
j = j+2;
};
else
i = j-1;
ex: is the following code
semantically clear?
if (i == j)
if (a == 2)
i = i+1;
else
j = j-1;
if (i == j)
if (a == 2)
i = i+1;
else
j = j-1;
rule : the else matches with nearest if.
So the first one is the “right” one.
Is this else-if statement?
if (….)
printf(…);
else if (…)
printf(….);
while-loop
syntax:
• while (expression)
statement
usage:
the as Java
for-loop
same as Java
syntax:
• for (expr1; expr2; expr3)
statement
next statement
meaning interpreted in terms of whileloop
expr1;
while (expr2)
{
statement;
expr3;
}
ex:
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.
ex:
functions (modular
programming)
#include <….>
function prototypes (optional )
function defs
main ()
{…..}
ex:
functions
recursive functions
Pointers, 1-d Arrays, Strings
Pointers
1-d arrays
Strings
• variables holding memory addresses
• vectors (same as Java)
• index starts from 0 (not 1)
• 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.
p
?
(NULL)
if p is a pointer, then *p (called pointer
dereferencing) means the memory
location (cell) which is pointed by p.
ex:
int q=1, *p;
p = &q;
p
*p
1
q
so,
int *p;
can be understood in both ways:
• as
(int *) p; i.e., p is variable of type int *.
or
• 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 does it not work?
type synonym : typedef
give a new name for existing types:
ex:
•
•
typedef char * string;
typedef int number;
• string s1;
• number n;
structure (or record)
syntax
• struct name
{
type field;
…..
}
name is optional
ex:
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