Unix Brief

Introduction to UNIX

What is UNIX?    

An Operating System (OS) Mostly coded in C Machine independence It provides a number of facilities:   

management of hardware resources directory and file system loading / execution / suspension of programs

History (Brief) 

1969   

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First UNIX at Bell Labs The MULTICS Kernighan, Ritchie, Thompson

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1970’s 

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Bell Labs makes UNIX freeware Berkeley UNIX (BSD) Bill Joy vi editor, C Shell

1980’s

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System V release 4 TCP/IP Sun Microsystems Solaris Microsoft Xenix, SCO MIT X-Windows

1990’s  

GNU, LINUX Stallman, Torvalds

Why Use UNIX?      

multi-tasking / multi-user lots of software networking capability graphical (with command line) easy to program portable (PCs, mainframes, super-computers) continued

  

 

free! (LINUX, FreeBSD, GNU) popular profitable 1996 Sales: US$34.5 Billion, up 12% not tied to one company active community

Your Account 

Each user has their own space called their account.



Type your login ID and password to enter your account.



Only if the login ID and password match will you be let in.

Login to your Account login: ad

You type your ID and RETURN.

Password:

You type your password and RETURN. It does not appear.

$

The UNIX prompt (or similar). You can now enter

commands.

Logout from your Account logout

or ^D

or exit

Press CONTROL and D together

On-line Help 

man

Manual pages Spacebar to go on; ^C to stop

man gnuchess man man 

apropos topic apropos game apropos help

Lists commands related to topic

UNIX Books 

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

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The Unix Programming Environment, Brian W. Kernighan and Rob Pike. Prentice Hall, Inc., 1984. Sumitabha Das, "Unix : Concepts and Applications" A Student’s Guide to UNIX, Harley Hahn, McGraw-Hill, 1993 A Practical Guide to the UNIX System, Mark G. Sobell, Benjamin-Cummings, 3rd Edition, 1995

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Kernel Compilers

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Kernel-Shell Relationship

The Shell  

The UNIX user interface is called the shell. The shell does 4 jobs repeatedly: display prompt read command

the shell process command

execute command

Typing Commands 

Try these: date cal 3 2005 who ls -a man cal clear

Changing your Password 

The command is: passwd



It will ask you for the new password twice.

Date Commands 

date

Gives time and date



cal

Calendar

cal 1997 cal 3 cal 7 1962 cal 9 1752

You and the System 

uptime



hostname

Machine’s ‘up’ time Name of the machine



whoami

Your name



who

Calculators 

expr e

Simple arithmetic

expr 3 + 5 + 7 

bc

Programmable Calculator

Some General Purpose Commands date cal who ls man clear uptime

locate more passwd echo banner tty uname

hostname

tput

quota

spell

whoami apropos whatis which

ispell cat sort pwd

Redirection, pipes , processes 

Output can be redirected to a file with‘>‘: ls > dir.txt cal 2004 > year2004



Output can be appended to a file with ‘>>‘ cal 2004 > years cal 2005 >> years



Pipes : sending the output of one program to the input of the other ls | sort who | sort

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Processes : Running two commands sequentially locate mj > xxx; date locate usr > xxx &

The UNIX File System

The File 

Ordinary Files



Directory Files



Device Files

The Parent Child Relationship 

A simplified UNIX directory/file system: /

etc ...

bin date . . . cal

usr1 faculty mj

dev ...

tmp ...

Some System Directories 

/

root directory



/bin

commands



/etc

system data files (e.g. /etc/passwd)

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/dev

files representing I/O devices

Pathnames 

A pathname is a sequence of directory names (separated by /’s) which identifies the location of a directory.

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There are two sorts of pathnames  

absolute pathnames relative pathname

Absolute Pathnames 



The sequence of directory names between the top of the tree (the root) and the directory of interest. For example: /bin /etc/terminfo /export/user/home/ad /export/user/home/s3910120/proj1

Relative Pathnames 

The sequence of directory names below the directory where you are now to the directory of interest.



If you are interested in the directory proj1: proj1 s3910120 s3910120/proj1 home/s3910120/proj1

if you are in if you are in home if you are in user

Commands and Pathnames 

Commands often use pathnames.



For example: /usr/games/fortune cat /etc/passwd

List the password file

Moving between Directories 

s3910120’s home directory:

s3910120 hobby.c

proj1

proj2

...

...



If you are in directory s3910120 how do you move to directory proj1? cd proj1



You are now in proj1. This is called the current working directory.

Print name of current working directory

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pwd



Move back to directory s3910120 (the parent directory): cd ..

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When in proj1, move to proj2 with one command: cd ../proj2

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../proj2 is a relative pathname

Special Directory Names  

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/ . directory ..

The root directory The current working The parent directory (of your current directory)

Examples 

cd /

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cd ~

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cd

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cd ../..

Change to root directory Change to home directory (Special case; means cd ~) Go up two levels.

Investigate the System 

Use cd



cat file

List file

cd /etc cat passwd 

ls ls ls /etc

Directory listing List current dir. List /etc

Making / Deleting / Renaming Directories



Usually, you can only create directories (or delete or rename them) in your home directory or directories below it. mkdir rmdir mv

Make a directory Delete a directory Rename a directory

Permissions 

ls –l /etc/passwd -rw-r--r--

 

root

2365 Jul 28 16:19 /etc/passwd

read, write, execute (r w x) rw- r-- r--

directory



1 root

owner

chmod -w, +w ….

group everyone

Commands to work with files           

cat > filename less head tail cp mv rm wc grep spell ispell

Communicating with People

Information on Others 

users

Who else is logged on?



who

Information on current users

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ps

What are people doing?

ps -au

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w w -sh

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What are people doing? A shorter report

Examine password info: more /etc/passwd grep s38 /etc/passwd

Fingering People 

finger finger -l

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finger user finger ad

Info. on current users Longer information

Information on user (need not be logged in)



finger @machine-name

User info. for that

machine finger @catsix finger @ratree.psu.ac.th 

ping machine-name ping catsix

Is machine alive (on)? (^C to stop)

Your Finger Information Change your finger entry

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chfn

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finger also prints the contents of the .plan and .project files in your home

directory. List ‘.’ files with: ls -a

Talking 

talk user

Talk to user (on any machine)

talk ad talk [email protected]

Get out by typing ^C



write user user

Send a message to on this machine

write ad



mesg n mesg y

Switch off talk / write acceptance. Switch on

Sending E-mail 

Send mail : mail Add

Subject: Shoe Problem What colour are my shoes? I cannot see them at the moment because of my desk. - Jim ^D

The vi Editor 

Two modes  

   

Insert i Command <ESC>

Append a Replace character r, Replace word R ….. Deleting character x, Deleting line dd Exit Goto command mode press :wq …… 

The Shell

Exploring the Shell 

Making a new command Create a directory called ‘bin’ inside your directory mkdir bin  Create a file containing a set of commands cat > nuls echo ‘Welcome to your directory’ ls –l echo ‘Thank you’ ^D  Make nuls executable Chmod +x nuls 



The Convention filename.sh

Exploring the Shell 

Command arguments and parameters    

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Argument 1 to 9 $1, ….,$9 All the arguments $* $0 – The name of the shell script $# - The Number of arguments

Shell Variables 

Set a variable Variable name = value $ x = Good Day $ echo $x $ set

Exploring the Shell 

Making the script interactive : read echo ‘Enter file name’ read fname echo $fname

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Exit status of a command 

$? - exit status 0 command succeeds  Any other non zero value command fails 

Exploring the Shell 

Conditional Execution. Delimits two commands  && : The second command is executed only when the first command is executed successfully  || : The second command is executed only when the first command fails.

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Script Termination 

exit

Exploring the Shell 

Conditional statements if (conditional is true) then execute commands else execute commands

fi Example if grep “professor” employee.list then echo “record found” else echo “record not found”

fi

Exploring the Shell 

Operator meaning -eq = -ne != -gt > -ge >= -lt < -le <=

Numeric comparison test $x –eq $y if test $# -eq 0 then echo "no input argument" else echo $1 fi

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String Comparison if [ -z "$1" ]; then echo "no input argument" else echo $1 fi

Test

True if

-n stg -z stg

stg is not a null string stg is a null string

s1 = s2

s1 = s2

s1 != s2

s1 != s2

stg

stg is assigned and not null

Exploring the Shell 

The case structure case expression in pattern1) Commands ;; pattern2) Commands ;; pattern9) Commands ;; esac

Exploring the Shell 

Computation  



expr 3 + 5 expr $x + $y

Command Termination  

P1 ; P2 - does P1 then P2 P1 & P2 - does P1 then P2 but does not wait for P1 to finish.

Exploring the Shell 

Looping



while (condition is true) do commands done 

Looping with a list for var in list do commands done

while true ; do date sleep 100; done &



for file in *.c do cc –o $file{x} $file done

Filters 

The UNIX programs that read some input, perform a simple transformation on it and write some output.

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grep, egrep, fgrep tr, dd, sort Sed, awk – programmable filters

 

grep 

grep options pattern format filename(s)



Some option    

-c Counting number of occurrences -n Line numbers along with lines grep Mamata –e mamata database grep [Mm]amata database

grep : Regular Expressions 

Character sets 

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Immediately preceeding character 



[mM] , [aeiou] , [a-zA-Z0-9] G*, [gG]*

Matching a single character  

2… A four character pattern starting with 2 .* A number of characters or none

grep : RE

c

^

Any non-special character c matches Turn off any special meaning of character c Beginning of line

$

End of line

.

Any single character

[…]

Any one of character in …; ranges like a-z are legal Any single character not in …; ranges are legal Zero or more occurrences of r RE r1 followed by RE r2

\c 

Specifying pattern boundaries 





^r pattern beginning with expression r ^[^r] pattern not beginning with expression r r$ pattern ending with expression r

[^…] r* r1r2

egrep : Regular Expressions    

r+ : one or more occurrences of r r? : zero or more occurrences of r r1|r2 : r1 or r2 (r) : nested r

fgrep   

Searches for multiple patterns Does not accept regular expression Multiple patterns are separated by new line character. The disadvantage of grep family is that none of them has a separate facility to identify fields.

sort 

    

-f : eliminates distinction between uppercase and lowercase letters. -n : numeric comparison - r : largest to smallest +m : comparison skips first m fields +0 : beginning of the line -u : discard duplicates

comm  

File comparison command Gives three columns of the output   



Lines that occur only in file 1 Lines that occur only in file 2 Lines that occur in both

One or more columns can be suppressed 

Comm –12 f1 f2

tr 

Transliteration of character in the input 



tr a-z A-N

Mostly used for character conversion

Assignment 1. Try all the UNIX commands. Store the output in a file appropriately using redirection operators. 2. Read a word from the terminal and check if the spelling is correct. Suggest few alternatives. 3. Create a file using Vi. Store few names in the file. Search all the names containing the letter M or m. 4. Create another file using cat command 5. Compare both the files to find the diffirences 6. Use calculator commands to compute 5 arithmetic expressions.