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SLC/UNI X/JULY20001

By the end of the session...

UNIX Operating system

Commands

Shell programming

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SLC/UNI X/JULY20002

Types of Shells

There are many shells (interpreters)

available on UNIX

There are 3 widely used shells namely:

Bourne shell

C Shell

Korn Shell or K-Shell

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Bourne Shell

Known after the inventor Steve Bourne

Very popular

Comes with UNIX

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SLC/UNI X/JULY20004

C Shell

Created by Bill Joy

Used by serious UNIX programmers

It allows aliasing of commands

Command history maintenance. This is

more like the DOS doskey.

These are the two key features

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Korn Shell

Also known as K-shell

Designed by David Korn of AT&T

Very powerful

Superset of Bourne shell

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Access to UNIX

Access to UNIX is given through login &

password

login:abc

password :xyz

login & password will be created by the

system administrator

password is not visible while typing

After 3 successive failures of login, the

login will be disabled

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Access to UNIX

If the login or password is not entered

correctly, it will give login incorrect

message

It wont tell which is not correct - login /password. This is a security measure

After the successful login, it will go to $

prompt for ordinary user, # prompt forsuper user

The prompt can be changed through PS1

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UNIX Commands

All UNIX commands should be entered

in lower case

Between the command and the

arguments, there must be at least onespace or tab

e.g.: ls -l

All command flags will be given with -

(Hyphen)

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UNIX Commands

One or more flags can be clubbed

e.g.: ls -l -acan be given as ls -la

DEL-key erases characters and cancels a

command

Terminal should not be turned-off as

soon as the work is over. Press ^d

(Ctrl+d) to come into login:prompt

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UNIX file system

Creation of login involves

Identifying login name to the user

Identifying initial password

Identify a group for the user

Identifying a default shell to the user

Identifying a working directory

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UNIX file system

UNIX understands everything as a file. It

may be disk, terminal, directory or file.

A file is a stream of bytes.

A file will have properties like block

special, character special devices etc.

A file system begins with a directory

called root

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UNIX file system - root directory

Denoted by / slash

Every directory will branch from root

Other directories under root directory

are bin, lib, usr, etc, tmp & dev

Contains the kernel (UNIX)

All directories will have files with specific

purpose

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UNIX file system - Structure

UsersHardware

Kernel

Shell

Tools & Applications

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UNIX file system - bin directory

Contains the binary files i.e. executables

UNIX commands are mostly C programs

or shell programs

Shell programs are collection of several

UNIX commands

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UNIX file system - lib directory

Contains library functions

The programmers under UNIX will use

these libraries

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UNIX file system - dev directory

Contains device driver files of input /

output

The devices like terminals, printers, disk

drivers etc

Separate file for each device

Each device is implemented as a file

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UNIX file system - usr directory

Contains several user directories

Created by system administrator when

creating new accounts

Each user is allowed to work in his

directory often known as home directory

User can organize his directory by

creating subdirectories

usr contains another bin directory

containing additional UNIX commands

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UNIX file system - tmp

Contains temporary files created by

UNIX or by other users

Will be deleted by UNIX at shutdown

time

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Date - Command

This command is used to display the currentSystem date or set the system date.Example :$ date

Thu Nov 8 03:13:18 MST 2007

$ date +%a

Thu

$ date +%A

Thursday

$ date +%b

Nov

$ date +%B

November

$ date +%d08

$ date +%D

11/08/07

$ date +"%r %a %d %b %y"

03:18:59 AM Thu 08 Nov 07

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Creating files

Can be created using two commands

touch & cat

$touchfile1 file2

Creates file-name-1, file-name-2 files

of zero size

Used to create several empty files

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Creating files - cat

$cat>file1

Whatever typed will go to the file file1

Press ^d (Ctrl+d) to abort the cat

command

^d inserts the EOF (End Of File)

character

$catfile1

Displays the contents of the file1

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Creating files - cat

To add to file3 by:

$catfile1 file2>>file3

Appends the contents of file1, file2 to file3

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CAT Command

Can create files

Can club files

Can be used to see the files

Can append to files

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File Copy Command - cp

To copy file1 to file2 by:

$cpfile1 file2

To copy files to directory

$cpfile1 file2 dir-name

Can copy files across directories by

providing absolute or relative path:

$cp/usr1/file1 /usr2/file1

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File Delete Command - rm

Removes the file

The file removed can not be recovered

like in DOS using undelete

Care should be taken while deleting:

$rmfile1

Removes file1

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File Delete Command - rm

$rm -ifile1

Removes file interactively. Removes after

confirmation

$rm -rdir1

Removes files from dir1 recursively

$rm -irdir1

Removes file from dir1 recursively and

interactively

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File Listing Command - ls

Provides the current directory listing:

$ls

Provides the directory contents:

$lsdir-name

Displays the file names in alphabetically

sorted order

Wont display the file names starting

with . period.

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To display all files including the filesstarting with .

$ls -a

To display only file-names starting with

a,b,c only

$ls [a-c]*

To display long listing

$ls -l

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$ls -l gives something like thistotal 32

-rwxr-x--x 1 usr1 group1 24 jan 00 10:13 file1

drwxr-x--x 1 usr1 group1 24 jan 00 10:13 file2

-rwxr-x--x 2 usr1 group1 24 jan 00 10:13 file3

total 32 means current directory

occupied 32 blocks

Generally each block in UNIX is 1024

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The next 9 characters provides theinformation about file permissions

Next column gives the number of links

Owner name

Group name

File size in bytes

Date & Time of last modified

Finally the file-name

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Owner concept comes with multi-user OS

The file creator is the owner by default

Group is formed with same type of users

Anybody other than the above are others The first 3 characters in permission field is

owner permissions

The next 3 characters tells about the grouppermissions

Last 3 characters gives the other permissions

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There are three types of permissions like

r- read permission

w- write permission

x- execution permission

rwxr-x--xmeans

Owner of this file has read, write and

execute permissions

Group has read and execute permissions

Others has only execution permissions

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File Change Permission - chmod

Existing file permissions can be changedwith the command chmod

To change the rwxr-x--x(751)

permissions to rwxrwxrwx(777)permissions of file1 is

$chmod777 file1

To give write permission to all

$chmod +wfile1

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File Change Permission - chmod

To remove write permissions to allincluding the owner

$chmod-wfile1

The above command is generally used to

keep a file safe by making it READ-

ONLY

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Directory Permissions

A directory is also a file for UNIX

Directory will have the permissions as

that of any file

A directory is writable if the user has

write permissions etc

754 are the most widely used permissions

for a directory

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Directory Commands - pwd

User goes to home directory uponsuccessful login

To know which directory we are

currently in:$pwd

pwd stands for present working directory

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Directory Commands - mkdir

To create a directory with givenpermissions:

$mkdir -m754 new-dir

new-dir will be created with 754

permissions

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UNIX commands - banner

Prints the given string in big letters

$banner

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UNIX commands - touch

Used to change the last access time of afile

$touch -afile1

Changes the access timeof file1 with

current time

$touchfile1

Changes access time as well as

modification time will be changed to

current time

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UNIX commands - file

Used to know the file type like shellscript, executable

$filefile-name

english text

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UNIX file commands - wc

Used to know the number of characters,number of files and number of lines in a

file

$wcfile1$wc -lfile1

Displays the number of lines in file1

Can take the input from terminal directly

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UNIX file commands - sort

Used to sort a file

$sortfile1

Sorts file1 and displays the sorted file on

terminal

Instead of displaying the sorted file on

terminal, can be written in to a file by:

$sort o file2 file1

Writes the sorted file1 in file2

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UNIX file commands - cut

Cut is a filter.

Picks up given number of bytes from a

given file by:

$cut -f5,10 file1

Displays 5th field to 10th field in file1.

Each field is assumed to be separated by

TAB character

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UNIX file commands - grep

This is the good example of unfriendlyUNIX command

Acronym for Globally search a Regular

Expression and Print it Searches for a pattern in file(s)

$grepabc file1

Searches for the string abc in file1

fi

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UNIX file commands - head

Displays only first few lines of a file asper the argument

$head -15file1

Displays only first 15 lines of file1

UNIX fil d il

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UNIX file commands - tail

Displays only last few lines of a file as perthe argument

$tail -15file1

Displays the last 15 lines of file1

UNIX fil d /

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UNIX file commands - pg/more

Both commands work almost like thesame with few differences

$pg +5 -20 -p -sfile1

Starts displaying file1 20 lines per page,starting from 5th line, with prompt for

each page of display

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UNIX fil d l t t

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UNIX file commands - lpstat

Gives the printer status like which iscurrently printing, how many jobs are

still in queue etc

$lpstat -tscheduler is running

system default destination : lp

device for lp: /dev/lp0lp accepting requests since

Queue information

UNIX fil d l

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UNIX file commands - cancel

Used to cancel the given print job$cancellp-15

request lp-15,226 cancelled

UNIX fil d

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UNIX file commands - compress

Two commands provided for filecompression namely compress and pack

They behave the same way

$compress -vfile1

file1: Compression: 90.1%

Compresses the file file1 and creates a file

by name file1.z

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UNIX fil d

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UNIX file commands - man

UNIX provides on-line manuals by:$man

Displays all the information about

I/O R di ti & Pi i

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I/O Redirection & Piping

I/O can be redirected using

symbol implies - write the output inthe file instead of display unit

2> symbols implies - write the error in a

file rather than display unit

e.g.:abcout-file 2>err-file

I/O R di ti & Pi i

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A >> indicates the appending of data toa file if it exists, instead of over-writing

1>&2indicates - redirect Standard Output

to Standard Er ror | means -

the standard output of Command-1 is

going to be the standard input ofCommand-2

I/O R di ti & Pi i

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UNIX supports joining of commandsthrough | piping character

$ls| wc -l

The output of ls is the input for wc

$ls | wc -l >outfile

Output of wc will be written in outfile


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Output of first process will be written topipe and the pipe then hands it over to

the next process.

tee can be used to capture the pipe file$who | tee file1 | sort

Output of who will be written into file1

and the file will be sorted and the sortedfile will be written to standard output

UNIX Command ps

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UNIX Command - ps

To see the processes running currentlyunder UNIX can be had by:

$ps

PID TTY TIME COMMAND2266 tty2 0:06 sh

2269 tty2 0.02 ps

Process Status command is shortlyknown as ps

UNIX Background Process

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Time consuming tasks may be run inbackground

Place & at the end of the command, the

process will go to background Displays the PID after submission

Success or failure of the background

process will not be reported


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Better to redirect the background processoutput to some file. Otherwise, it will

disturb the foreground process messages

on the screen Too many background processes will

degrade the performance

If logged out, all the backgroundprocesses will be terminated

UNIX Command Sleep

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UNIX Command - Sleep

This command is used to delay a process for a periodof timeFor Example :

To run a command at regular intervals, enter:

while true

do

date

sleep 60

done

This shell procedure displays the date and time once a minute.

To stop it, press the Interrupt key sequence.

Killing a Process

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Killing a Process

To terminate a process$killPID

An user can kill only his processes

UNIX Communication write

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UNIX Communication - write

Any user can write a message on otherusers terminal.

Other user should give permissions to

write message$write

hello

^d (Ctrl+d)

Hellowill be written on user-names

terminal

UNIX Communication write

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UNIX Communication - write

The user should be logged-in to receive the message

The recipient should give permissions for

message Message writing can be denied by:

$mesg-n

Super user can write to any terminal

without permissions

UNIX Communication finger

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UNIX Communication - finger

Can find who are the users who setmessage -n by:

$finger -i

Login TTY When Idleabc *tty1

def tty2

ghi tty3 a * before the tty means - set mesg -n

UNIX Communication motd

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UNIX Communication - motd

The Message of the day news will betyped in a file called /etc/motd. The

contents will be displayed upon login.

News like The system will be taken formaintenance from 14.00 Hrs to 16.00

Hrs so that the users will schedule their

work accordingly.

Shell Programming

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Shell Programming

A shell program is a series of UNIXcommands

Instead of typing the commands one after

the other, the commands may be writtenin a file and execute the file.

Shell programming offers much more

versatility than mere UNIX commands Almost a system can be developed by

using shell script with UNIX commands

Shell Programming

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Shell Programming

UNIX shell is the interface between theoperating system & user

It is an interpreter, not an executable

A shell script can be executed by givingexecute permissions ($chmod +x shell) or

by shell command ($sh shell)

Shell programming is so powerful, evensystem shutdown like tasks can be

handled

Shell Programming

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Shell Programming

Three shells available under UNIX -Bourne, C & Korn shell

The following shell scripts were written

in Bourne shell Bourne shell script will work with Korn

shell and the reverse is not true

Bourne is the default shell in most of theinstallations

Shell Programming

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Shell Programming

Shell scripts are used to accomplishvariety of tasks like:

Customizing the working environment

Automating the daily tasks like backupsetc

Automating repetitive tasks

Executing important system procedureslike shutdown

Shell Programming

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Shell Programming

When the user logins into the system, theUNIX starts a shell (sh) on that terminal

which accepts commands from $

prompt When a shell-script is given for execution,

the shell executes the commands from the

shell-script

Interactive Shell Programming

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Two basic words in shell are read& echo read accepts input

echo writes the output

echo Enter your name \?

read name

echo Good morning $name

Write the above 3 lines in a file name

sh01

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name is a shell variable receives datafrom keyboard

$name will display the contents of the

variable


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echo Enter three values X Y Zread x y z

echo $x $y $z

If 1 2 3 entered, x will have 1, 2 to y & 3 to z

If 1 2 3 4 are entered, then z will have 3 4

If only 1, 2 are entered, then z will be assigned

null value

If more arguments entered, last variable will beassigned rest. If less, null will be assigned


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echo This is new line \nAnd this is secondline

The above will be displayed as

This is new lineAnd this is second line

The escape sequence was brought from C

language


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\b is blank, \t is tab char etc. To make the cursor at the end of the

echoed line

echo Enter your Name :\c

Enter your Name :_ (Cursor waits here)

echo \007 gives bell

Shell Variables

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Shell Variables

They are an integral part of shellprogramming

Provide ability to store and manipulate

data Fully under the control of the shell

Can create and destroy the variables as

the user wants

Shell Variables - Guidelines

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Shell Variables Guidelines

Any combination of alphabet, numbersand underscore(_ )

No editing characters like commas,

blanks The first character of the name should be

alpha or underscore

May be of any reasonable length Case sensitive ie abc & Abc are different

Shell - Assigning values

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Shell Assigning values

Values can be assigned to variable using= equal sign

$name=Vijay

$echo $namedisplays Vijay

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System Variables

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System Variables

UNIX defines certain variables for itsown usage

e.g.: PS1 stands for prompt string1

$PS1=ABC

From this time onwards, UNIX displays

ABC as prompt

System Variables

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System Variables

PS2 is prompt string 2, default value is>

PATH defines the directories to searched

by shell to execute any command or file HOME defines the default working

directory

LOGNAME stores the log name of theuser

System Variable

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System Variable

MAIL stores the file name of the mailboxalong path

MAILCHECK duration of the mail

checking SHELL keeps the default shell name

System Variables

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Sys e V b es

TERM gives the name of the terminal theuser is using

All the above variable values can be

known by set command$set

Displays all the values

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Tips & Traps

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p p

Can display more than one variable in aline

$echo Name is $nameand age is $age

All variables in a shell script areautomatic variable. i.e. they will be

created as soon as the shell script

execution starts and dies as soon as theexecution is over

Tips & Traps

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p p

A null variable can be created by$a1= or a1= or a1=

Shell ignore if any shell variable is having

null value

Unchanging Variable - readonly

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g g y

User can make a variable unchangedduring execution by:

$age=20

$readonlyage The the shell does not allow us to change

the value

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Positional Parameters

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Many occasions, a program expects thevariables in a certain fashion. This is

achieved through positional parameters

from $0 through $9. $0is the program itself. Thus

$abc par1 par2 par3 par4 assigns

abc to $0, par1 to $1 par4 to $4

Passing command line arguments

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g g

To write a shell by name sh02 whichcopies one file to another

echo Copying $1 to $2

cp $1 $2 By executing sh02

$sh02 file1 file2

Copying file1 to file2. Positional parameters can not assigned values

like $1=100

Shell Variables

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To know the number of variables givenfor the shell through $#

$abc file1 file

echo $# The above shell displays 3

Shell Variables - shift

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Shell can handle only 9 variables at a time. Toaccess more than 9, the shift command is used

$set You have the capacity to learn the shell

programming in a very easy way

$echo $10 displays You0 as shell interprets $10

as $1 with 0.

$shift 5 : makes the 5th argument as $1

argument. Thus $echo $1 displays learn

$* handles all positional parameters


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$ set a b c d e f g h i j k l m n o p$ echo $1 $2 $3 $4 $5 $6 $7 $8 $9

a b c d e f g h i

$ shift 7

$ echo $1 $2 $3 $4 $5 $6 $7 $8 $9

h I j k l m n o p


If the number of parameters are greater than nineThe shiftcommand can be used to shift the parameters

For Example :

Arithmetic in Shell

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Write the following in a file and execute:

a=10 b=4

echo expr $a + $b

echo expr $a - $b

echo expr $a \* $b

echo expr $a / $b

echo expr $a % $b #modulus

Arithmetic in Shell

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On execution, the output is:

14

6

40

2

2

Arithmetic in Shell

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Anything after # sign will be treated ascomment

expris the key word for doing arithmetic

A multiplication symbol (*) should bepreceded by \

Terms in expr should be separated by

space Parenthesis may be used for clarity of

expression

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UNIX decision loops

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There are 4 decision making loops

if then fi

if then else fi

if then elif else fi

case - esac

UNIX - if then fi

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Key word ifand the delimiter is fi

if

then

statements

fi

e.g.: if cp $1 $2

then echo Copied successfully

fi

UNIX - if then else fi

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The structure of this construct is:

if

then

statements

else

statements

fi

UNIX - if then else fi

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e.g.:if cp $1 $2

then

echo File copiedsuccessfully

else

echo File copy failed

fi

Example if else - fi

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# Example of numeric testecho Enter basic salary

read bs

if [ $bs -lt 2500 ]

then

hra=echo $bs \* 10 / 100 | bc

da=echo $bs \* 90 / 100 bc

else

hra=500

da=echo $bs \* 98 / 100 | bc

fi

gs=echo $bs + $hra + $da | bc

echo Gross salary = Rs. $gs

UNIX - if then elif else fi

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Used for multilevel decision making.

if then

statements

elif

statements

else

statements

fi

UNIX - test

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if depends upon the exit status of thecommand given

test verbs translates the result into

success or failure There are three tests namely

Numerical test

String test

File test

UNIX - test - numerical

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Used to compare numerical

-gt= greater than

-lt = less than

-ge= greater than or equal to

-le = less than or equal to

-ne= not equal

-eq= equal

UNIX - test - numerical

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if [ $1 -lt 5 ]then

echo the value is < 5

elif [ $1 -le 7 ]

echo the value is 7

fi

UNIX - test

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Use square braces to avoid writing test

Provide a space after [

Provide a space before ]

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UNIX - test - String

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s1 = s2 returns true if both are same -n returns true if string length > 0

if [ $1 = $2 ] then

echo Both strings are same

else

echo $?

fi

$?Contains the value of the last command

0 = true, 1 = false

UNIX logical conditions

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-astands for AND condition

-ostands for OR condition

-!Is negation

if -a

Returns true if both the conditions are

true

if [ $1 -gt 60 ] -a [ $2 -lt 50 ]then

statements...

UNIX case

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To handle multiple choices

casevalue in

choice 1) statements;;

choice 2) statements;;

*) statements;;

esac

UNIX case

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esac is the delimiter of case

Used for menus

*) is the default choice

All choice statements should beterminated by double semicolon(;;)

UNIX case example

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case $option in1) echo Financial accounting;;

2) echo Materiel accounting;;

*) echo Invalid Opt - Try;;

esac

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UNIX case

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Multiple options can be groupede.g.:

case $1 in

banana | orange) echo Fruit;;dog | pig) echo Animal;;

lion) echo Wild animal;;

esac

UNIX case

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Can use shells pattern matchinge.g.:

case $1 in

[a-z]) echo Small alpha;;[A-Z]) echo Capital;;

esac

UNIX Loop Controls

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Provided 3 loop constructs namely: whileloop

forloop

untilloop

UNIX - whileloop

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while do

statements

done done is the delimiter of do

UNIX - while example

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count = 1while [ $count -le 3 ]

do

echo Loop value $countcount = `expr $count + 1`

done

Examples of while loop

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# calculation of simple interest

count=1

while [ $count -le 3 ]do

echo \nEnter p,n,r\c

read p n r

si=echo $p \* $n \* $r /100 | bc

echo Simple interest = Rs.$si

count=expr $count + 1

done

# printing numbers using while

i=1

while [ $i -le 10 ]

doecho $i

i=expr $i + 1

done

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UNIX - until loop

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until do

statements

done

until continues its loop so long as the

condition is false

except this, while & until are identical

Example - until loop

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# printing numbers using until

i=1

until [ $i -gt 10 ]

do

echo $1

i=expr $i + 1

done

UNIX - for loop

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Most frequently used loopfor control-var in value1

value2

dostatements

done

for takes a list of variables

UNIX - for example

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for word in $*do

echo $word

done

Examplefor loop

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Example

# To print names of all sub-directories

for entry in *

do

if [ -d $entry ]then

echo $entry

fi

done

UNIX - break statement

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Used to break the current loop and comesout of the loop

Usually associated with i f

if [ $1 -eq 5 ]then

I = 2

break

fi

UNIX - continue statement

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To take the control to the beginning ofthe loop bypassing the statements

I=1

while [ $I -le 5 ] thendo

I = `expr $I + 1`

continue

done

UNIX - Metacharacters

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Called as regular expressions. Classified as follows:

File name : ? * [] [!]

I/O redirection : < > >> m>&n

Process execution: ; ( ) & && ||

Positional paras : $1..$9

Spl characters : $0 $* $@ $# $! $$ $-

UNIX - File name

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ls??- lists all files with 2 chars long lsa*- lists all file names begin with a

ls[a-c]*-file names begin with a,b &c

ls[!a-c]- file names not starting witha,b,c

UNIX - I/O Redirection

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write output to

>>append output

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Tips & Traps

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Try to use the absolute paths in the shellscripts. This saves the search time of the

system for the command

Remove write permissions to files thatare important. This even prevents the

accidental update of the files

Compress the print/report files. These

files occupies lot of disk space. Better

pack them and keep

Tips & Traps

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The compressed print files can be printeddirectly without uncompress them by

using the pcat command

$pcattextfile.txt.z > /dev/lp0 The above command will send the print

file directly to printer

Tips & Traps

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Untouched files in the directory may befound using findcommand.

$find . -mtime 10 -print

displays the files that are untouched forthe last 10 days

Clean up of the directory should be done

periodically. Otherwise, any amount diskspace will be inadequate.

UNIX

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Thank Q

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