Shell tutorial

Written by Vivek G. Gite.
Cyberciti Computers & nixCraft, Pune, INDIA.

This Document is Copyright (C) 1999-2002, Vivek G. Gite.

Linux Shell Scripting Tutorial v1.05r3 - A Beginner's handbook

Linux Shell Scripting
Tutorial v1.05r3
A Beginner's handbook
Copyright © 1999-2002 by Vivek G. Gite
<vivek@nixcraft.com>

(Formally know as www.vivek-tech.com)

Table of Contents
Chapter 1: Quick Introduction to Linux
What Linux is?
Who developed the Linux?
How to get Linux?
How to Install Linux
Where I can use Linux?
What Kernel Is?
What is Linux Shell?
How to use Shell
What is Shell Script ?
Why to Write Shell Script ?
More on Shell...
Chapter 2: Getting started with Shell Programming
How to write shell script
Variables in shell
How to define User defined variables (UDV)
Rules for Naming variable name (Both UDV and System Variable)
How to print or access value of UDV (User defined variables)
echo Command

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Shell Arithmetic
More about Quotes
Exit Status
The read Statement
Wild cards (Filename Shorthand or meta Characters)
More commands on one command line
Command Line Processing
Why Command Line arguments required
Redirection of Standard output/input i.e. Input - Output redirection
Pipes
Filter
What is Processes
Why Process required
Linux Command(s) Related with Process
Chapter 3: Shells (bash) structured Language Constructs
Decision making in shell script ( i.e. if command)
test command or [ expr ]
if...else...fi
Nested ifs
Multilevel if-then-else
Loops in Shell Scripts
for loop
Nested for loop
while loop
The case Statement
How to de-bug the shell script?
Chapter 4: Advanced Shell Scripting Commands
/dev/null - to send unwanted output of program
Local and Global Shell variable (export command)
Conditional execution i.e. && and ||
I/O Redirection and file descriptors
Functions
User Interface and dialog utility-Part I
User Interface and dialog utility-Part II
Message Box (msgbox) using dialog utility
Confirmation Box (yesno box) using dialog utility
Input (inputbox) using dialog utility
User Interface using dialog Utility - Putting it all together
trap command
The shift Command



getopts command
Chapter 5: Essential Utilities for Power User
Preparing for Quick Tour of essential utilities
Selecting portion of a file using cut utility
Putting lines together using paste utility
The join utility
Translating range of characters using tr utility
Data manipulation using awk utility
sed utility - Editing file without using editor
Removing duplicate lines from text database file using uniq utility
Finding matching pattern using grep utility
Chapter 6: Learning expressions with ex
Getting started with ex
Printing text on-screen
Deleting lines
Copying lines
Searching the words
Find and Replace (Substituting regular expression)
Replacing word with confirmation from user
Finding words
Using range of characters in regular expressions
Using & as Special replacement character
Converting lowercase character to uppercase
Chapter 7: awk Revisited
Getting Starting with awk
Predefined variables of awk
Doing arithmetic with awk
User Defined variables in awk
Use of printf statement
Use of Format Specification Code
if condition in awk
Loops in awk
Real life examples in awk
awk miscellaneous
sed - Quick Introduction
Redirecting the output of sed command
How to write sed scripts?
More examples of sed
Chapter 8: Examples of Shell Scripts



Logic Development:
Shell script to print given numbers sum of all digit
Shell script to print contains of file from given line number to next given number of lines
Shell script to say Good morning/Afternoon/Evening as you log in to system
Shell script to find whether entered year is Leap or not
Sort the given five number in ascending order (use of array)
Command line (args) handling:
Adding 2 nos. suppiled as command line args
Calculating average of given numbers on command line args
Finding out biggest number from given three nos suppiled as command line args
Shell script to implement getopts statement.
Basic math Calculator (case statement)
Loops using while & for loop:
Print nos. as 5,4,3,2,1 using while loop
Printing the patterns using for loop.
Arithmetic in shell scripting:
Performing real number calculation in shell script
Converting decimal number to hexadecimal number
Calculating factorial of given number
File handling:
Shell script to determine whether given file exist or not.
Screen handling/echo command with escape sequence code:
Shell script to print "Hello World" message, in Bold, Blink effect, and in different colors like red,
brown etc.
Background process implementation:
Digital clock using shell script
User interface and Functions in shell script:
Shell script to implements menu based system.
System Administration:
Getting more information about your working environment through shell script
Shell script to gathered useful system information such as CPU, disks, Ram and your environment
etc.
Shell script to add DNS Entery to BIND Database with default Nameservers, Mail Servers (MX)
and host
Integrating awk script with shell script:
Script to convert file names from UPPERCASE to lowercase file names or vice versa.
Chapter 9: Other Resources
Appendix - A : Linux File Server Tutorial (LFST) version b0.1 Rev. 2
Appendix - B : Linux Command Reference (LCR)
About the author
About this Document



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Up Quick Introduction to Linux

( Cyeberciti Computers & nixCraft has years of experince in Linux / Unix / FreeBSD. If you need any
assistance, education, support for Linux / Unix, write to sales@cyberciti.biz )


LSST v1.05r3 > Chapter 1 > Quick Introduction to Linux

Linux Shell Scripting Tutorial (LSST) v1.05r3
Prev Chapter 1: Introduction: Quick Introduction to Linux Next

Introduction
This tutorial is designed for beginners who wish to learn the basics of shell scripting/programming plus
introduction to power tools such as awk, sed, etc. It is not help or manual for the shell; while reading this
tutorial you can find manual quite useful (type man bash at $ prompt to see manual pages). Manual
contains all necessary information you need, but it won't have that much examples, which makes idea
more clear. For this reason, this tutorial contains examples rather than all the features of shell.

Audience for this tutorial
I assumes you have at least working knowledge of Linux i.e. basic commands like how to create, copy,
remove files/directories etc or how to use editor like vi or mcedit and login to your system. But not
expects any programming language experience. If you have access to Linux, this tutorial will provide
you an easy-to-follow introduction to shell scripting.

What's different about this tutorial
Many other tutorial and books on Linux shell scripting are either too basic, or skips important
intermediate steps. But this tutorial, maintained the balance between these two. It covers the many real
life modern example of shell scripting which are almost missed by many other
tutorials/documents/books. I have used a hands-on approach in this tutorial. The idea is very clear "do it
yourself or learn by doing" i.e. trying things yourself is the best way to learn, so examples are presented
as complete working shell scripts, which can be typed in and executed

Chapter Organization
Chapter 1 to 4 shows most of the useful and important shell scripting concepts. Chapter 5 introduction to
tools & utilities which can be used while programming the Linux shell smartly. Chapter 6 and 7 is all
about expression and expression mostly used by tools such as sed and awk. Chapter 8 is loaded with tons
of shell scripting examples divided into different categories. Chapter 9 gives more resources information
which can be used while learning the shell scripting like information on Linux file system, common
Linux command reference and other resources.
Chapter 1 introduces to basic concepts such as what is Linux, where Linux can used and continue
explaning the shell, shell script and kernel etc.
Chapter 2 shows how to write the shell script and execute them. It explains many basic concepts which
requires to write shell script.

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LSST v1.05r3 > Chapter 1 > Quick Introduction to Linux

Chapter 3 is all about making decision in shell scripting as well as loops in shell. It explains what
expression are, how shell understands the condition/decisions. It also shows you nesting concept for if
and for loop statement and debugging of shell script.
Chapter 4 introduces the many advanced shell scripting concepts such as function, user interface, File
Descriptors, signal handling, Multiple command line arguments etc.
Chapter 5 introduces to powerful utility programs which can be used variety of purpose while
programming the shell.

Chapter 6 and 7 gives more information on patterns, filters, expressions, and off course sed and awk is
covered in depth.
Chapter 8 contains lot of example of shell scripting divided into various category such as logic
development, system administration etc.

Note that indicates advanced shell scripting concepts, you can skip this if you are really new to Linux
or Programming, though this is not RECOMMENDED by me.
I hope you get as much pleasure reading this tutorial, as I had writing it. After reading this tutorial if you
are able to write your own powerful shell scripts, then I think the purpose of writing this tutorial is served
and finally if you do get time after reading this tutorial drop me an e-mail message about your
comment/suggestion/questions and off course bugs (errors) you find regarding this tutorial.

Prev Home Next
Up What Linux is?


LSST v1.05r3 > Chapter 1 > What Linux is?


What Linux is?
q Free
q Unix Like
q Open Source
q Network operating system

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Up Who developed the Linux?

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LSST v1.05r3 > Chapter 1 > Who developed the Linux?


Who developed the Linux?
In 1991, Linus Torvalds studying Unix at the University, where he used special educational experimental
purpose operating system called Minix (small version of Unix and used in Academic environment). But
Minix had it's own limitations. Linus felt he could do better than the Minix. So he developed his own
version of Minix, which is now know as Linux. Linux is Open Source From the start of the day. For
more information on Linus Torvalds, please visit his home page.

Prev Home Next
What Linux is? Up How to get Linux?


LSST v1.05 > Chapter 1 > How to get Linux?


How to get Linux?
Linux available for download over the net, this is useful if your internet connection is fast. Another way
is order the CD-ROMs which saves time, and the installation from CD-ROM is fast/automatic. Various
Linux distributions available. Following are important Linux distributions.
Linux distributions. Website/Logo

Red Hat Linux:
http://www.redhat.com/

SuSE Linux: http://www.suse.com/

Mandrake Linux:
http://www.mandrakesoft.com/

Caldera Linux:
http://www.calderasystems.com/

Debian GNU/Linux:
http://www.debian.org/

Slackware Linux:
http://www.slackware.com/

Note: If you are in India then you can get Linux Distribution from the Leading Computer magazine such
as PC Quest (Even PCQuest has got its own Linux flavour) or if you are in Pune, India please visit our
web site to obtained the Red Hat Linux or any other official Linux distribution. Note that you can also
obtained your Linux distribution with Linux books which you purchase from local book store.

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LSST v1.05 > Chapter 1 > How to get Linux?

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Who developed the Linux? Up How to Install Linux


LSST v1.05 > Chapter 1 > How to Install Linux ?


How to Install Linux ?
Please visit the LESSBS Project home page for Quick Visual Installation Guide for Red Hat Linux
version 6.2 and 7.2.

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How to get Linux? Up Where I can use Linux?


LSST v1.05 > Chapter 1 > Where I can use Linux?

Prev Chapter 1: Introduction : Linux Shell basics Next

Where I can use Linux?
You can use Linux as Server Os or as stand alone Os on your PC. (But it is best suited for Server.) As a
server Os it provides different services/network resources to client. Server Os must be:
q Stable

q Robust

q Secure

q High Performance

Linux offers all of the above characteristics plus its Open Source and Free OS. So Linux can be used as:
(1) On stand alone workstation/PC for word processing, graphics, software development, internet,
e-mail, chatting, small personal database management system etc.
(2) In network environment as:
(A) File and Print or Application Server
Share the data, Connect the expensive device like printer and share it, e-mail within the LAN/intranet etc
are some of the application.

Linux Server with different Client Os

(B) Linux sever can be connected to Internet, So that PC's on intranet can share the internet/e-mail etc.
You can put your web sever that run your web site or transmit the information on the internet.


LSST v1.05 > Chapter 1 > Where I can use Linux?

Linux Server can act as Proxy/Mail/WWW/Router Server etc.

So you can use Linux for:
q Personal Work

q Web Server

q Software Development Workstation

q Workgroup Server

q In Data Center for various server activities such as FTP, Telnet, SSH, Web, Mail, Proxy, Proxy
Cache Appliance etc
See the LESSBS project for more information on Linux Essential Services (as mentioned above) and
how to implement them in easy manner for you or your organization.

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How to Install Linux Up What Kernel Is?


LSST v1.05 > Chapter 1 > LSST v1.05 > Chapter 1 >


What Kernel Is?
Kernel is heart of Linux Os.
It manages resource of Linux Os. Resources means facilities available in Linux. For e.g. Facility to store
data, print data on printer, memory, file management etc .
Kernel decides who will use this resource, for how long and when. It runs your programs (or set up to
execute binary files).
The kernel acts as an intermediary between the computer hardware and various
programs/application/shell.

It's Memory resident portion of Linux. It performance following task :-
q I/O management

q Process management

q Device management

q File management

q Memory management

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Where I can use Linux? Up What is Linux Shell?


LSST v1.05 > Chapter 1 > What is Linux Shell ?


What is Linux Shell ?
Computer understand the language of 0's and 1's called binary language.
In early days of computing, instruction are provided using binary language, which is difficult for all of
us, to read and write. So in Os there is special program called Shell. Shell accepts your instruction or
commands in English (mostly) and if its a valid command, it is passed to kernel.
Shell is a user program or it's a environment provided for user interaction. Shell is an command language
interpreter that executes commands read from the standard input device (keyboard) or from a file.
Shell is not part of system kernel, but uses the system kernel to execute programs, create files etc.
Several shell available with Linux including:
Shell Name Developed by Where Remark
BASH ( Bourne-Again Brian Fox and Chet Free Software Most common shell in
SHell ) Ramey Foundation Linux. It's Freeware
shell.
CSH (C SHell) Bill Joy University of California The C shell's syntax and
(For BSD) usage are very similar to
the C programming
language.
KSH (Korn SHell) David Korn AT & T Bell Labs --
TCSH See the man page. -- TCSH is an enhanced
Type $ man tcsh but completely
compatible version of
the Berkeley UNIX C
shell (CSH).

Tip: To find all available shells in your system type following command:
$ cat /etc/shells
Note that each shell does the same job, but each understand a different command syntax and provides
different built-in functions.
In MS-DOS, Shell name is COMMAND.COM which is also used for same purpose, but it's not as
powerful as our Linux Shells are!
Any of the above shell reads command from user (via Keyboard or Mouse) and tells Linux Os what users
want. If we are giving commands from keyboard it is called command line interface ( Usually in-front of
$ prompt. This prompt is depend upon your shell and Environment that you set or by your System
Administrator, therefore you may get different prompt ).


LSST v1.05 > Chapter 1 > What is Linux Shell ?

Tip: To find your current shell type following command
$ echo $SHELL

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What Kernel Is? Up How to use Shell


LSST v1.05 > Chapter 1 > How to use Shell


How to use Shell
To use shell (You start to use your shell as soon as you log into your system) you have to simply type
commands.
See common Linux Command for syntax and example, this can be used as quick reference while

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What is Linux Shell? Up What is Shell Script ?


LSST v1.05 > Chapter 1 > What is Shell Script ?


What is Shell Script ?
Normally shells are interactive. It means shell accept command from you (via keyboard) and execute
them. But if you use command one by one (sequence of 'n' number of commands) , the you can store this
sequence of command to text file and tell the shell to execute this text file instead of entering the
commands. This is know as shell script.
Shell script defined as:
"Shell Script is series of command written in plain text file. Shell script is just like batch file is MS-DOS
but have more power than the MS-DOS batch file."

Prev Home Next
How to use Shell Up Why to Write Shell Script ?


LSST v1.05 > Chapter 1 > Why to Write Shell Script ?


Why to Write Shell Script ?
q Shell script can take input from user, file and output them on screen.
q Useful to create our own commands.
q Save lots of time.
q To automate some task of day today life.
q System Administration part can be also automated.

Prev Home Next
What is Shell Script ? Up More on Shell...


LSST v1.05 > Chapter 1 > Linux Shell basics


Which Shell We are using to write Shell
Script ?
In this tutorial we are using bash shell.

Objective of this Tutorial (LSST v.1.5)
Try to understand Linux Os
Try to understand the basics of Linux shell
Try to learn the Linux shell programming

What I need to learn this Tutorial (LSST
v.1.5)
Linux OS ( I have used Red Hat Linux distribution Version 6.x+)
Web Browse to read tutorial. (IE or Netscape) For PDF version you need PDF reader.
Linux - bash shell. (Available with almost all Linux Distributions. By default bash is default shell for
Red Hat Linux Distribution). All the scripts are also tested on Red Hat Linux version 7.2.

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Why to Write Shell Script ? Up Getting started with Shell Programming


LSST v1.05r3 > Chapter 2 > Getting started with Shell Programming

Prev Chapter 2: Getting started with Shell Programming Next

Getting started with Shell Programming
In this part of tutorial you are introduced to shell programming, how to write script, execute them etc.
We will be getting started with writing small shell script, that will print "Knowledge is Power" on screen.
Before starting with this you should know
q How to use text editor such as vi, see the common vi command for more information.

q Basic command navigation

Prev Home Next
More on Shell... Up How to write shell script

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LSST v1.05r3 > Chapter 2 > How to write shell script
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How to write shell script
Following steps are required to write shell script:
(1) Use any editor like vi or mcedit to write shell script.
(2) After writing shell script set execute permission for your script as follows
syntax:
chmod permission your-script-name
Examples:
$ chmod +x your-script-name
$ chmod 755 your-script-name
Note: This will set read write execute(7) permission for owner, for group and other permission is read and execute only(5).
(3) Execute your script as
syntax:
bash your-script-name
sh your-script-name
./your-script-name
Examples:
$ bash bar
$ sh bar
$ ./bar
NOTE In the last syntax ./ means current directory, But only . (dot) means execute given command file in current shell
without starting the new copy of shell, The syntax for . (dot) command is as follows
Syntax:
. command-name
Example:
$ . foo
Now you are ready to write first shell script that will print "Knowledge is Power" on screen. See the common vi command
list , if you are new to vi.
$ vi first
#
# My first shell script
#
clear
echo "Knowledge is Power"
After saving the above script, you can run the script as follows:
$ ./first


LSST v1.05r3 > Chapter 2 > How to write shell script

This will not run script since we have not set execute permission for our script first; to do this type command
$ chmod 755 first
$ ./first
First screen will be clear, then Knowledge is Power is printed on screen.
Script Command(s) Meaning
$ vi first Start vi editor
# followed by any text is considered as
comment. Comment gives more
#
information about script, logical
# My first shell script
explanation about shell script.
#
Syntax:
# comment-text
clear clear the screen
To print message or value of variables on
screen, we use echo command, general
echo "Knowledge is Power" form of echo command is as follows
syntax:
echo "Message"

How Shell Locates the file (My own bin directory to execute script)
Tip: For shell script file try to give file extension such as .sh, which can be easily identified by you as shell script.
Exercise:
1)Write following shell script, save it, execute it and note down it's output.
$ vi ginfo
#
#
# Script to print user information who currently login , current date
& time
#
clear
echo "Hello $USER"
echo "Today is c ";date
echo "Number of user login : c" ; who | wc -l
echo "Calendar"
cal
exit 0
Future Point: At the end why statement exit 0 is used? See exit status for more information.

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Getting started with Shell Programming Up Variables in Shell
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LSST v1.05r3 > Chapter 2 > Variables in Shell


Variables in Shell
To process our data/information, data must be kept in computers RAM memory. RAM memory is
divided into small locations, and each location had unique number called memory location/address,
which is used to hold our data. Programmer can give a unique name to this memory location/address
called memory variable or variable (Its a named storage location that may take different values, but only
one at a time).
In Linux (Shell), there are two types of variable:
(1) System variables - Created and maintained by Linux itself. This type of variable defined in
CAPITAL LETTERS.
(2) User defined variables (UDV) - Created and maintained by user. This type of variable defined in
lower letters.
You can see system variables by giving command like $ set, some of the important System variables are:
System Variable Meaning
BASH=/bin/bash Our shell name
BASH_VERSION=1.14.7(1) Our shell version name
COLUMNS=80 No. of columns for our screen
HOME=/home/vivek Our home directory
LINES=25 No. of columns for our screen
LOGNAME=students students Our logging name
OSTYPE=Linux Our Os type
PATH=/usr/bin:/sbin:/bin:/usr/sbin Our path settings
PS1=[u@h W]$ Our prompt settings
PWD=/home/students/Common Our current working directory
SHELL=/bin/bash Our shell name
USERNAME=vivek User name who is currently login to this PC

NOTE that Some of the above settings can be different in your PC/Linux environment. You can print any
of the above variables contains as follows:
$ echo $USERNAME
$ echo $HOME
Exercise:
1) If you want to print your home directory location then you give command:
a) $ echo $HOME
OR


LSST v1.05r3 > Chapter 2 > Variables in Shell

(b) $ echo HOME
Which of the above command is correct & why? Click here for answer.

Caution: Do not modify System variable this can some time create problems.

Prev Home Next
How to define User defined variables
How to write shell script Up
(UDV)


LSST v1.05r3 > Chapter 2 > How to define User defined variables (UDV)


How to define User defined variables
(UDV)
To define UDV use following syntax
Syntax:
variable name=value
'value' is assigned to given 'variable name' and Value must be on right side = sign.

Example:
$ no=10 # this is ok
$ 10=no # Error, NOT Ok, Value must be on right side of = sign.
To define variable called 'vech' having value Bus
$ vech=Bus
To define variable called n having value 10
$ n=10

Prev Home Next
Rules for Naming variable name (Both
Variables in shell Up
UDV and System Variable)


LSST v1.05r3 > Chapter 2 > Rules for Naming variable name (Both UDV and System Variable)


Rules for Naming variable name (Both
(1) Variable name must begin with Alphanumeric character or underscore character (_), followed by one
or more Alphanumeric character. For e.g. Valid shell variable are as follows
HOME
SYSTEM_VERSION
vech
no
(2) Don't put spaces on either side of the equal sign when assigning value to variable. For e.g. In
following variable declaration there will be no error
$ no=10
But there will be problem for any of the following variable declaration:
$ no =10
$ no= 10
$ no = 10
(3) Variables are case-sensitive, just like filename in Linux. For e.g.
$ no=10
$ No=11
$ NO=20
$ nO=2
Above all are different variable name, so to print value 20 we have to use $ echo $NO and not any of the
following
$ echo $no # will print 10 but not 20
$ echo $No # will print 11 but not 20
$ echo $nO # will print 2 but not 20
(4) You can define NULL variable as follows (NULL variable is variable which has no value at the time
of definition) For e.g.
$ vech=
$ vech=""
Try to print it's value by issuing following command
$ echo $vech
Nothing will be shown because variable has no value i.e. NULL variable.
(5) Do not use ?,* etc, to name your variable names.

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LSST v1.05r3 > Chapter 2 > Rules for Naming variable name (Both UDV and System Variable)

How to define User defined variables How to print or access value of UDV
Up
(UDV) (User defined variables)


LSST v1.05r3 > Chapter 2 > How to print or access value of UDV (User defined variables)


How to print or access value of UDV
(User defined variables)
To print or access UDV use following syntax
Syntax:
$variablename
Define variable vech and n as follows:
$ vech=Bus
$ n=10
To print contains of variable 'vech' type
$ echo $vech
It will print 'Bus',To print contains of variable 'n' type command as follows
$ echo $n
Caution: Do not try $ echo vech, as it will print vech instead its value 'Bus' and $ echo n, as it will print
n instead its value '10', You must use $ followed by variable name.
Exercise
Q.1.How to Define variable x with value 10 and print it on screen.
Q.2.How to Define variable xn with value Rani and print it on screen
Q.3.How to print sum of two numbers, let's say 6 and 3?
Q.4.How to define two variable x=20, y=5 and then to print division of x and y (i.e. x/y)
Q.5.Modify above and store division of x and y to variable called z
Q.6.Point out error if any in following script
$ vi variscript
#
#
# Script to test MY knowledge about variables!
#
myname=Vivek
myos = TroubleOS
myno=5
echo "My name is $myname"
echo "My os is $myos"
echo "My number is myno, can you see this number"
For Answers Click here

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LSST v1.05r3 > Chapter 2 > How to print or access value of UDV (User defined variables)

Rules for Naming variable name (Both Up echo Command


LSST v1.05r3 > Chapter 2 > echo Command


echo Command
Use echo command to display text or value of variable.
echo [options] [string, variables...]
Displays text or variables value on screen.
Options
-n Do not output the trailing new line.
-e Enable interpretation of the following backslash escaped characters in the strings:
a alert (bell)
b backspace
c suppress trailing new line
n new line
r carriage return
t horizontal tab
backslash
For e.g. $ echo -e "An apple a day keeps away attdoctorn"

How to display colorful text on screen with bold or blink effects, how to print text on any row, column
on screen, click here for more!

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How to print or access value of UDV (User Up Shell Arithmetic
defined variables)


LSST v1.05r3 > Chapter 2 > Shell Arithmetic


Shell Arithmetic
Use to perform arithmetic operations.
Syntax:
expr op1 math-operator op2

Examples:
$ expr 1 + 3
$ expr 2 - 1
$ expr 10 / 2
$ expr 20 % 3
$ expr 10 * 3
$ echo `expr 6 + 3`
Note:
expr 20 %3 - Remainder read as 20 mod 3 and remainder is 2.
expr 10 * 3 - Multiplication use * and not * since its wild card.
For the last statement not the following points
(1) First, before expr keyword we used ` (back quote) sign not the (single quote i.e. ') sign. Back quote is
generally found on the key under tilde (~) on PC keyboard OR to the above of TAB key.
(2) Second, expr is also end with ` i.e. back quote.
(3) Here expr 6 + 3 is evaluated to 9, then echo command prints 9 as sum
(4) Here if you use double quote or single quote, it will NOT work
For e.g.
$ echo "expr 6 + 3" # It will print expr 6 + 3
$ echo 'expr 6 + 3' # It will print expr 6 + 3

See Parameter substitution - To save your time.

Prev Home Next
echo Command Up More about Quotes


LSST v1.05r3 > Chapter 2 > More about Quotes


More about Quotes
There are three types of quotes
Quotes Name Meaning
"Double Quotes" - Anything enclose in double quotes removed meaning of that
" Double Quotes
characters (except and $).
' Single quotes 'Single quotes' - Enclosed in single quotes remains unchanged.
` Back quote
`Back quote` - To execute command

Example:
$ echo "Today is date"
Can't print message with today's date.
$ echo "Today is `date`".
It will print today's date as, Today is Tue Jan ....,Can you see that the `date` statement uses back quote?

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Shell Arithmetic Up Exit Status


LSST v1.05r3 > Chapter 2 > Exit Status


Exit Status
By default in Linux if particular command/shell script is executed, it return two type of values which is
used to see whether command or shell script executed is successful or not.
(1) If return value is zero (0), command is successful.
(2) If return value is nonzero, command is not successful or some sort of error executing command/shell
script.
This value is know as Exit Status.
But how to find out exit status of command or shell script?
Simple, to determine this exit Status you can use $? special variable of shell.
For e.g. (This example assumes that unknow1file doest not exist on your hard drive)
$ rm unknow1file
It will show error as follows
rm: cannot remove `unkowm1file': No such file or directory
and after that if you give command
$ echo $?
it will print nonzero value to indicate error. Now give command
$ ls
$ echo $?
It will print 0 to indicate command is successful.
Exercise
Try the following commands and not down the exit status:
$ expr 1 + 3
$ echo $?
$ echo Welcome
$ echo $?
$ wildwest canwork?
$ echo $?
$ date
$ echo $?
$ echon $?
$ echo $?

$? useful variable, want to know more such Linux variables click here to explore them!


LSST v1.05r3 > Chapter 2 > Exit Status

Prev Home Next
More about Quotes Up The read Statement


LSST v1.05r3 > Chapter 2 > The read Statement


The read Statement
Use to get input (data from user) from keyboard and store (data) to variable.
Syntax:
read variable1, variable2,...variableN
Following script first ask user, name and then waits to enter name from the user via keyboard. Then user
enters name from keyboard (after giving name you have to press ENTER key) and entered name through
keyboard is stored (assigned) to variable fname.
$ vi sayH
#
#Script to read your name from key-board
#
echo "Your first name please:"
read fname
echo "Hello $fname, Lets be friend!"
Run it as follows:
$ chmod 755 sayH
$ ./sayH
Your first name please: vivek
Hello vivek, Lets be friend!

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Wild cards (Filename Shorthand or meta
Exit Status Up
Characters)


LSST v1.05r3 > Chapter 2 > Wild cards (Filename Shorthand or meta Characters)


Wild cards (Filename Shorthand or meta
Characters)

Wild card
Meaning Examples
/Shorthand
$ ls * will show all files
will show all files whose first
$ ls a*
name is starting with letter 'a'
Matches any string or group of will show all files having
* $ ls *.c
characters. extension .c
will show all files having
$ ls ut*.c extension .c but file name must
begin with 'ut'.
will show all files whose names
$ ls ?
are 1 character long
? Matches any single character. will show all files whose names
$ ls fo? are 3 character long and file name
begin with fo
Matches any one of the will show all files beginning with
[...] $ ls [abc]*
enclosed characters letters a,b,c

Note:
[..-..] A pair of characters separated by a minus sign denotes a range.
Example:
$ ls /bin/[a-c]*
Will show all files name beginning with letter a,b or c like
/bin/arch /bin/awk /bin/bsh /bin/chmod /bin/cp
/bin/ash /bin/basename /bin/cat /bin/chown /bin/cpio
/bin/ash.static /bin/bash /bin/chgrp /bin/consolechars /bin/csh
But
$ ls /bin/[!a-o]
$ ls /bin/[^a-o]
If the first character following the [ is a ! or a ^ ,then any character not enclosed is matched i.e. do not
show us file name that beginning with a,b,c,e...o, like


LSST v1.05r3 > Chapter 2 > Wild cards (Filename Shorthand or meta Characters)

/bin/ps /bin/rvi /bin/sleep /bin/touch /bin/view
/bin/pwd /bin/rview /bin/sort /bin/true /bin/wcomp
/bin/red /bin/sayHello /bin/stty /bin/umount /bin/xconf
/bin/remadmin /bin/sed /bin/su /bin/uname /bin/ypdomainname
/bin/rm /bin/setserial /bin/sync /bin/userconf /bin/zcat
/bin/rmdir /bin/sfxload /bin/tar /bin/usleep
/bin/rpm /bin/sh /bin/tcsh /bin/vi

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The read Statement Up More command on one command line


LSST v1.05r3 > Chapter 2 > More command on one command line


More command on one command line
Syntax:
command1;command2
To run two command with one command line.
Examples:
$ date;who
Will print today's date followed by users who are currently login. Note that You can't use
$ date who
for same purpose, you must put semicolon in between date and who command.

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Wild cards (Filename Shorthand or meta Up Command Line Processing
Characters)


LSST v1.05r3 > Chapter 2 > Command Line Processing


Command Line Processing
Try the following command (assumes that the file "grate_stories_of" is not exist on your system)
$ ls grate_stories_of
It will print message something like - grate_stories_of: No such file or directory.
ls is the name of an actual command and shell executed this command when you type command at shell
prompt. Now it creates one more question What are commands? What happened when you type $ ls
grate_stories_of ?
The first word on command line is, ls - is name of the command to be executed.
Everything else on command line is taken as arguments to this command. For e.g.
$ tail +10 myf
Name of command is tail, and the arguments are +10 and myf.
Exercise
Try to determine command and arguments from following commands
$ ls foo
$ cp y y.bak
$ mv y.bak y.okay
$ tail -10 myf
$ mail raj
$ sort -r -n myf
$ date
$ clear
Answer:
No. of argument to this command
Command Actual Argument
(i.e $#)
ls 1 foo
cp 2 y and y.bak
mv 2 y.bak and y.okay
tail 2 -10 and myf
mail 1 raj
sort 3 -r, -n, and myf
date 0
clear 0

NOTE:
$# holds number of arguments specified on command line. And $* or $@ refer to all arguments passed to


LSST v1.05r3 > Chapter 2 > Command Line Processing

script.

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More commands on one command line Up Why Command Line arguments required


LSST v1.05r3 > Chapter 2 > Why Command Line arguments required


Why Command Line arguments required
1. Telling the command/utility which option to use.
2. Informing the utility/command which file or group of files to process (reading/writing of files).
Let's take rm command, which is used to remove file, but which file you want to remove and how you
will tell this to rm command (even rm command don't ask you name of file that you would like to
remove). So what we do is we write command as follows:
$ rm {file-name}
Here rm is command and filename is file which you would like to remove. This way you tail rm
command which file you would like to remove. So we are doing one way communication with our
command by specifying filename. Also you can pass command line arguments to your script to make it
more users friendly. But how we access command line argument in our script.
Lets take ls command
$ Ls -a /*
This command has 2 command line argument -a and /* is another. For shell script,
$ myshell foo bar

Shell Script name i.e. myshell

First command line argument passed to myshell i.e. foo

Second command line argument passed to myshell i.e. bar

In shell if we wish to refer this command line argument we refer above as follows

myshell it is $0

foo it is $1

bar it is $2



Here $# (built in shell variable ) will be 2 (Since foo and bar only two Arguments), Please note at a time
such 9 arguments can be used from $1..$9, You can also refer all of them by using $* (which expand to
`$1,$2...$9`). Note that $1..$9 i.e command line arguments to shell script is know as "positional
parameters".
Exercise
Try to write following for commands
Shell Script Name ($0),
No. of Arguments (i.e. $#),
And actual argument (i.e. $1,$2 etc)
$ sum 11 20
$ math 4 - 7
$ d
$ bp -5 myf +20
$ Ls *
$ cal
$ findBS 4 8 24 BIG
Answer

Shell Script Name No. Of Arguments to script Actual Argument ($1,..$9)
$0 $# $1 $2 $3 $4 $5
sum 2 11 20
math 3 4 - 7
d 0
bp 3 -5 myf +20
Ls 1 *
cal 0
findBS 4 4 8 24 BIG

Following script is used to print command ling argument and will show you how to access them:
$ vi demo
#!/bin/sh
#
# Script that demos, command line args
#
echo "Total number of command line argument are $#"
echo "$0 is script name"
echo "$1 is first argument"
echo "$2 is second argument"
echo "All of them are :- $* or $@"
Run it as follows



Set execute permission as follows:
$ chmod 755 demo
Run it & test it as follows:
$ ./demo Hello World
If test successful, copy script to your own bin directory (Install script for private use)
$ cp demo ~/bin
Check whether it is working or not (?)
$ demo
$ demo Hello World
NOTE: After this, for any script you have to used above command, in sequence, I am not going to show
you all of the above command(s) for rest of Tutorial.
Also note that you can't assigne the new value to command line arguments i.e positional parameters.
So following all statements in shell script are invalid:
$1 = 5
$2 = "My Name"

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Redirection of Standard output/input
Command Line Processing Up
i.e.Input - Output redirection


LSST v1.05r3 > Chapter 2 > Redirection of Standard output/input i.e. Input - Output redirection


Redirection of Standard output/input i.e.
Input - Output redirection
Mostly all commands give output on screen or take input from keyboard, but in Linux (and in other OSs
also) it's possible to send output to file or to read input from file.
For e.g.
$ ls command gives output to screen; to send output to file of ls command give command

$ ls > filename
It means put output of ls command to filename.
There are three main redirection symbols >,>>,<
(1) > Redirector Symbol
Syntax:
Linux-command > filename
To output Linux-commands result (output of command or shell script) to file. Note that if file already
exist, it will be overwritten else new file is created. For e.g. To send output of ls command give
$ ls > myfiles
Now if 'myfiles' file exist in your current directory it will be overwritten without any type of warning.
(2) >> Redirector Symbol
Syntax:
Linux-command >> filename
To output Linux-commands result (output of command or shell script) to END of file. Note that if file
exist , it will be opened and new information/data will be written to END of file, without losing previous
information/data, And if file is not exist, then new file is created. For e.g. To send output of date
command to already exist file give command
$ date >> myfiles
(3) < Redirector Symbol
Syntax:
Linux-command < filename
To take input to Linux-command from file instead of key-board. For e.g. To take input for cat command
give
$ cat < myfiles

Click here to learn more about I/O Redirection
You can also use above redirectors simultaneously as follows
Create text file sname as follows


LSST v1.05r3 > Chapter 2 > Redirection of Standard output/input i.e. Input - Output redirection

$cat > sname
vivek
ashish
zebra
babu
Press CTRL + D to save.
Now issue following command.
$ sort < sname > sorted_names
$ cat sorted_names
ashish
babu
vivek
zebra
In above example sort ($ sort < sname > sorted_names) command takes input from sname file and
output of sort command (i.e. sorted names) is redirected to sorted_names file.
Try one more example to clear your idea:
$ tr "[a-z]" "[A-Z]" < sname > cap_names
$ cat cap_names
VIVEK
ASHISH
ZEBRA
BABU
tr command is used to translate all lower case characters to upper-case letters. It take input from sname
file, and tr's output is redirected to cap_names file.
Future Point : Try following command and find out most important point:
$ sort > new_sorted_names < sname
$ cat new_sorted_names

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Why Command Line arguments required Up Pipe


LSST v1.05r3 > Chapter 2 > Pipes


Pipes
A pipe is a way to connect the output of one program to the input of another program without any
temporary file.

Pipe Defined as:
"A pipe is nothing but a temporary storage place where the output of one command is stored and then
passed as the input for second command. Pipes are used to run more than two commands ( Multiple
commands) from same command line."
Syntax:
command1 | command2
Examles:

Command using Pipes Meaning or Use of Pipes
Output of ls command is given as input to more
$ ls | more command So that output is printed one screen full
page at a time.
Output of who command is given as input to sort
$ who | sort
command So that it will print sorted list of users
Same as above except output of sort is send to
$ who | sort > user_list
(redirected) user_list file
Output of who command is given as input to wc
$ who | wc -l command So that it will print number of user who
logon to system
Output of ls command is given as input to wc
$ ls -l | wc -l command So that it will print number of files in
current directory.


LSST v1.05r3 > Chapter 2 > Pipes

Output of who command is given as input to grep
command So that it will print if particular user
$ who | grep raju
name if he is logon or nothing is printed (To see
particular user is logon or not)

Prev Home Next
Redirection of Standard output/input Up Filter
i.e.Input - Output redirection


LSST v1.05r3 > Chapter 2 > Filter


Filter
If a Linux command accepts its input from the standard input and produces its output on standard output
is know as a filter. A filter performs some kind of process on the input and gives output. For e.g..
Suppose you have file called 'hotel.txt' with 100 lines data, And from 'hotel.txt' you would like to print
contains from line number 20 to line number 30 and store this result to file called 'hlist' then give
command:
$ tail +20 < hotel.txt | head -n30 >hlist
Here head command is filter which takes its input from tail command (tail command start selecting from
line number 20 of given file i.e. hotel.txt) and passes this lines as input to head, whose output is
redirected to 'hlist' file.
Consider one more following example
$ sort < sname | uniq > u_sname
Here uniq is filter which takes its input from sort command and passes this lines as input to uniq; Then
uniqs output is redirected to "u_sname" file.

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Pipes Up What is Processes


LSST v1.05r3 > Chapter 2 > What is Processes


What is Processes
Process is kind of program or task carried out by your PC. For e.g.
$ ls -lR
ls command or a request to list files in a directory and all subdirectory in your current directory - It is a
process.
Process defined as:
"A process is program (command given by user) to perform specific Job. In Linux when you start
process, it gives a number to process (called PID or process-id), PID starts from 0 to 65535."

Prev Home Next
Filter Up Why Process required


LSST v1.05r3 > Chapter 2 > Why Process required


As You know Linux is multi-user, multitasking Os. It means you can run more than two process
simultaneously if you wish. For e.g. To find how many files do you have on your system you may give
command like:

$ ls / -R | wc -l
This command will take lot of time to search all files on your system. So you can run such command in
Background or simultaneously by giving command like

$ ls / -R | wc -l &
The ampersand (&) at the end of command tells shells start process (ls / -R | wc -l) and run it in
background takes next command immediately.
Process & PID defined as:
"An instance of running command is called process and the number printed by shell is called process-id
(PID), this PID can be use to refer specific running process."

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What is Processes Up Linux Command(s) Related with Process


LSST v1.05r3 > Chapter 3 > Linux Command Related with Process


Linux Command Related with Process
Following tables most commonly used command(s) with process:
For this purpose Use this Command Examples*
To see currently running process ps $ ps
To stop any process by PID i.e. to
kill {PID} $ kill 1012
kill process
To stop processes by name i.e. to kill
killall {Process-name} $ killall httpd
process
To get information about all running
ps -ag $ ps -ag
process
To stop all process except your shell kill 0 $ kill 0
For background processing (With &,
use to put particular command and linux-command & $ ls / -R | wc -l &
program in background)
To display the owner of the
ps aux $ ps aux
processes along with the processes
For e.g. you want to see
To see if a particular process is whether Apache web server
running or not. For this purpose you
ps ax | grep process-U-want-to see process is running or not
have to use ps command in then give command
combination with the grep command
$ ps ax | grep httpd
To see currently running processes
and other information like memory top $ top
and CPU usage with real time See the output of top command.
Note that to exit from top
updates. command press q.
To display a tree of processes pstree $ pstree

* To run some of this command you need to be root or equivalnt user.
NOTE that you can only kill process which are created by yourself. A Administrator can almost kill
95-98% process. But some process can not be killed, such as VDU Process.
Exercise:
You are working on your Linux workstation (might be learning LSST or some other work like sending
mails, typing letter), while doing this work you have started to play MP3 files on your workstation.
Regarding this situation, answer the following question:


LSST v1.05r3 > Chapter 3 > Linux Command Related with Process

1) Is it example of Multitasking?
2) How you will you find out the both running process (MP3 Playing & Letter typing)?
3) "Currently only two Process are running in your Linux/PC environment", Is it True or False?, And
how you will verify this?
4) You don't want to listen music (MP3 Files) but want to continue with other work on PC, you will take
any of the following action:
1. Turn off Speakers
2. Turn off Computer / Shutdown Linux Os
3. Kill the MP3 playing process
4. None of the above
Click here for answers.

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Up Shells (bash) structured Language
Constructs


LSST v1.05r3 > Chapter 3 > Introducation

Prev Chapter 3: Shells (bash) structured Language Constructs Next

Introduction
Making decision is important part in ONCE life as well as in computers logical driven program. In fact
logic is not LOGIC until you use decision making. This chapter introduces to the bash's structured
language constructs such as:
q Decision making

q Loops

Is there any difference making decision in Real life and with Computers? Well real life decision are quite
complicated to all of us and computers even don't have that much power to understand our real life
decisions. What computer know is 0 (zero) and 1 that is Yes or No. To make this idea clear, lets play
some game (WOW!) with bc - Linux calculator program.
$ bc
After this command bc is started and waiting for your commands, i.e. give it some calculation as follows
type 5 + 2 as:
5+2
7
7 is response of bc i.e. addition of 5 + 2 you can even try
5-2
5/2
See what happened if you type 5 > 2 as follows
5>2
1
1 (One?) is response of bc, How? bc compare 5 with 2 as, Is 5 is greater then 2, (If I ask same question to
you, your answer will be YES), bc gives this 'YES' answer by showing 1 value. Now try
5<2
0
0 (Zero) indicates the false i.e. Is 5 is less than 2?, Your answer will be no which is indicated by bc by
showing 0 (Zero). Remember in bc, relational expression always returns true (1) or false (0 - zero).

Try following in bc to clear your Idea and not down bc's response
5 > 12
5 == 10
5 != 2
5 == 5
12 < 2
Expression Meaning to us Your Answer BC's Response
5 > 12 Is 5 greater than 12 NO 0
5 == 10 Is 5 is equal to 10 NO 0
5 != 2 Is 5 is NOT equal to 2 YES 1


LSST v1.05r3 > Chapter 3 > Introducation

5 == 5 Is 5 is equal to 5 YES 1
1<2 Is 1 is less than 2 Yes 1

It means when ever there is any type of comparison in Linux Shell It gives only two answer one is YES
and NO is other.
In Linux Shell Value Meaning Example
Zero Value (0) Yes/True 0

-1, 32, 55 anything but
NON-ZERO Value No/False
not zero

Remember both bc and Linux Shell uses different ways to show True/False values
Value Shown in bc as Shown in Linux Shell as
True/Yes 1 0
False/No 0 Non - zero value

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Linux Command(s) Related with Process Up if condition


LSST v1.05r3 > Chapter 3 > if condition


if condition
if condition which is used for decision making in shell script, If given condition is true then command1 is
executed.
Syntax:

if condition
then
command1 if condition is true or if exit status
of condition is 0 (zero)
...
...
fi
Condition is defined as:
"Condition is nothing but comparison between two values."

For compression you can use test or [ expr ] statements or even exist status can be also used.

Expreession is defined as:
"An expression is nothing but combination of values, relational operator (such as >,<, <> etc) and
mathematical operators (such as +, -, / etc )."

Following are all examples of expression:
5>2
3+6
3 * 65
a<b
c>5
c > 5 + 30 -1
Type following commands (assumes you have file called foo)
$ cat foo
$ echo $?
The cat command return zero(0) i.e. exit status, on successful, this can be used, in if condition as follows,
Write shell script as



$ cat > showfile
#!/bin/sh
#
#Script to print file
#
if cat $1
then
echo -e "nnFile $1, found and successfully echoed"
fi
Run above script as:
$ chmod 755 showfile
$./showfile foo
Shell script name is showfile ($0) and foo is argument (which is $1).Then shell compare it as follows:
if cat $1 which is expanded to if cat foo.
Detailed explanation
if cat command finds foo file and if its successfully shown on screen, it means our cat command is
successful and its exist status is 0 (indicates success), So our if condition is also true and hence statement
echo -e "nnFile $1, found and successfully echoed" is proceed by shell. Now if cat command is not
successful then it returns non-zero value (indicates some sort of failure) and this statement echo -e
"nnFile $1, found and successfully echoed" is skipped by our shell.
Exercise
Write shell script as follows:
cat > trmif
#
# Script to test rm command and exist status
#
if rm $1
then
echo "$1 file deleted"
fi
Press Ctrl + d to save
$ chmod 755 trmif

Answer the following question in referance to above script:
(A) foo file exists on your disk and you give command, $ ./trmfi foo what will be output?
(B) If bar file not present on your disk and you give command, $ ./trmfi bar what will be output?
(C) And if you type $ ./trmfi What will be output?
For Answer click here.

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Shells (bash) structured Language Up test command or [ expr ]
Constructs


LSST v1.05r3 > Chapter 3 > test command or [ expr ]


test command or [ expr ]
test command or [ expr ] is used to see if an expression is true, and if it is true it return zero(0), otherwise
returns nonzero for false.
Syntax:
test expression OR [ expression ]

Example:
Following script determine whether given argument number is positive.
$ cat > ispositive
#!/bin/sh
#
# Script to see whether argument is positive
#
if test $1 -gt 0
then
echo "$1 number is positive"
fi
Run it as follows
$ chmod 755 ispostive
$ ispostive 5
5 number is positive
$ispostive -45
Nothing is printed
$ispostive
./ispostive: test: -gt: unary operator expected
The line, if test $1 -gt 0 , test to see if first command line argument($1) is greater than 0. If it is true(0)
then test will return 0 and output will printed as 5 number is positive but for -45 argument there is no
output because our condition is not true(0) (no -45 is not greater than 0) hence echo statement is skipped.
And for last statement we have not supplied any argument hence error ./ispostive: test: -gt: unary
operator expected, is generated by shell , to avoid such error we can test whether command line argument
is supplied or not.
test or [ expr ] works with
1.Integer ( Number without decimal point)
2.File types
3.Character strings



For Mathematics, use following operator in Shell Script
Mathematical Normal Arithmetical/
Operator in Shell Meaning Mathematical But in Shell
Script Statements
For test For [ expr ]
statement with statement with
if command if command
-eq is equal to 5 == 6 if test 5 -eq 6 if [ 5 -eq 6 ]
-ne is not equal to 5 != 6 if test 5 -ne 6 if [ 5 -ne 6 ]
-lt is less than 5<6 if test 5 -lt 6 if [ 5 -lt 6 ]
is less than or
-le 5 <= 6 if test 5 -le 6 if [ 5 -le 6 ]
equal to
-gt is greater than 5>6 if test 5 -gt 6 if [ 5 -gt 6 ]
is greater than
-ge 5 >= 6 if test 5 -ge 6 if [ 5 -ge 6 ]
or equal to

NOTE: == is equal, != is not equal.
For string Comparisons use
Operator Meaning
string1 = string2 string1 is equal to string2
string1 != string2 string1 is NOT equal to string2
string1 string1 is NOT NULL or not defined
-n string1 string1 is NOT NULL and does exist
-z string1 string1 is NULL and does exist

Shell also test for file and directory types
Test Meaning
-s file Non empty file
-f file Is File exist or normal file and not a directory
-d dir Is Directory exist and not a file
-w file Is writeable file
-r file Is read-only file
-x file Is file is executable

Logical Operators
Logical operators are used to combine two or more condition at a time
Operator Meaning
! expression Logical NOT
expression1 -a expression2 Logical AND



expression1 -o expression2 Logical OR

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Decision making in shell script ( i.e. if Up if...else...fi
command)


LSST v1.05r3 > Chapter 3 > if...else...fi


if...else...fi
If given condition is true then command1 is executed otherwise command2 is executed.
Syntax:
if condition
then
condition is zero (true - 0)
execute all commands up to else statement

else
if condition is not true then
execute all commands up to fi
fi
For e.g. Write Script as follows:
$ vi isnump_n
#!/bin/sh
#
# Script to see whether argument is positive or negative
#
if [ $# -eq 0 ]
then
echo "$0 : You must give/supply one integers"
exit 1
fi

if test $1 -gt 0
then
echo "$1 number is positive"
else
echo "$1 number is negative"
fi
Try it as follows:
$ chmod 755 isnump_n

$ isnump_n 5
5 number is positive

$ isnump_n -45



-45 number is negative

$ isnump_n
./ispos_n : You must give/supply one integers

$ isnump_n 0
0 number is negative
First script checks whether command line argument is given or not, if not given then it print error
message as "./ispos_n : You must give/supply one integers". if statement checks whether number of
argument ($#) passed to script is not equal (-eq) to 0, if we passed any argument to script then this if
statement is false and if no command line argument is given then this if statement is true. The echo
command i.e.
echo "$0 : You must give/supply one integers"
| |
| |
1 2
1 will print Name of script
2 will print this error message
And finally statement exit 1 causes normal program termination with exit status 1 (nonzero means script
is not successfully run).
The last sample run $ isnump_n 0 , gives output as "0 number is negative", because given argument is
not > 0, hence condition is false and it's taken as negative number. To avoid this replace second if
statement with if test $1 -ge 0.

Nested if-else-fi
You can write the entire if-else construct within either the body of the if statement of the body of an else
statement. This is called the nesting of ifs.
$ vi nestedif.sh
osch=0

echo "1. Unix (Sun Os)"
echo "2. Linux (Red Hat)"
echo -n "Select your os choice [1 or 2]? "
read osch

if [ $osch -eq 1 ] ; then

echo "You Pick up Unix (Sun Os)"

else #### nested if i.e. if within if ######



if [ $osch -eq 2 ] ; then
echo "You Pick up Linux (Red Hat)"
else
echo "What you don't like Unix/Linux OS."
fi
fi
Run the above shell script as follows:
$ chmod +x nestedif.sh
$ ./nestedif.sh
1. Unix (Sun Os)
2. Linux (Red Hat)
Select you os choice [1 or 2]? 1
You Pick up Unix (Sun Os)
$ ./nestedif.sh
1. Unix (Sun Os)
2. Linux (Red Hat)
You Pick up Linux (Red Hat)
$ ./nestedif.sh
1. Unix (Sun Os)
2. Linux (Red Hat)
What you don't like Unix/Linux OS.
Note that Second if-else constuct is nested in the first else statement. If the condition in the first if
statement is false the the condition in the second if statement is checked. If it is false as well the final else
statement is executed.
You can use the nested ifs as follows also:
Syntax:

if condition
then
if condition
then
.....
..
do this
else
....
..
do this
fi
else



...
.....
do this
fi

Prev Home Next
test command or [ expr ] Up Multilevel if-then-else


LSST v1.05r3 > Chapter 3 > Multilevel if-then-else


Multilevel if-then-else
Syntax:
if condition
then
condition is zero (true - 0)
execute all commands up to elif statement
elif condition1
then
condition1 is zero (true - 0)
elif condition2
then
condition2 is zero (true - 0)
else
None of the above condtion,condtion1,condtion2 are true (i.e.
all of the above nonzero or false)
execute all commands up to fi
fi
For multilevel if-then-else statement try the following script:
$ cat > elf
#
#!/bin/sh
# Script to test if..elif...else
#
if [ $1 -gt 0 ]; then
echo "$1 is positive"
elif [ $1 -lt 0 ]
then
echo "$1 is negative"
elif [ $1 -eq 0 ]
then
echo "$1 is zero"
else
echo "Opps! $1 is not number, give number"
fi
Try above script as follows:
$ chmod 755 elf
$ ./elf 1
$ ./elf -2
$ ./elf 0
$ ./elf a
Here o/p for last sample run:
./elf: [: -gt: unary operator expected
./elf: [: -lt: unary operator expected
./elf: [: -eq: unary operator expected
Opps! a is not number, give number


LSST v1.05r3 > Chapter 3 > Multilevel if-then-else

Above program gives error for last run, here integer comparison is expected therefore error like "./elf: [: -gt: unary operator
expected" occurs, but still our program notify this error to user by providing message "Opps! a is not number, give number".

Prev Home Next
if...else...fi Up Loops in Shell Scripts


LSST v1.05r3 > Chapter 3 > Loops in Shell Scripts


Loops in Shell Scripts
Loop defined as:
"Computer can repeat particular instruction again and again, until particular condition satisfies. A
group of instruction that is executed repeatedly is called a loop."
Bash supports:
q for loop

q while loop

Note that in each and every loop,
(a) First, the variable used in loop condition must be initialized, then execution of the loop begins.
(b) A test (condition) is made at the beginning of each iteration.
(c) The body of loop ends with a statement that modifies the value of the test (condition) variable.

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Multilevel if-then-else Up for loop


LSST v1.05r3 > Chapter 3 > for Loop


for Loop
Syntax:
for { variable name } in { list }
do
execute one for each item in the list until the list is
not finished (And repeat all statement between do and done)
done
Before try to understand above syntax try the following script:
$ cat > testfor
for i in 1 2 3 4 5
do
echo "Welcome $i times"
done
Run it above script as follows:
$ chmod +x testfor
$ ./testfor
The for loop first creates i variable and assigned a number to i from the list of number from 1 to 5, The shell execute
echo statement for each assignment of i. (This is usually know as iteration) This process will continue until all the items
in the list were not finished, because of this it will repeat 5 echo statements. To make you idea more clear try following
script:
$ cat > mtable
#!/bin/sh
#
#Script to test for loop
#
#
if [ $# -eq 0 ]
then
echo "Error - Number missing form command line argument"
echo "Syntax : $0 number"
echo "Use to print multiplication table for given number"
exit 1
fi
n=$1
for i in 1 2 3 4 5 6 7 8 9 10
do
echo "$n * $i = `expr $i * $n`"
done
Save above script and run it as:
$ chmod 755 mtable
$ ./mtable 7
$ ./mtable
For first run, above script print multiplication table of given number where i = 1,2 ... 10 is multiply by given n (here



command line argument 7) in order to produce multiplication table as
7*1=7
7 * 2 = 14
...
..
7 * 10 = 70
And for second test run, it will print message -
Error - Number missing form command line argument
Syntax : ./mtable number
Use to print multiplication table for given number
This happened because we have not supplied given number for which we want multiplication table, Hence script is
showing Error message, Syntax and usage of our script. This is good idea if our program takes some argument, let the
user know what is use of the script and how to used the script.
Note that to terminate our script we used 'exit 1' command which takes 1 as argument (1 indicates error and therefore
script is terminated)
Even you can use following syntax:
Syntax:
for (( expr1; expr2; expr3 ))
do
.....
...
repeat all statements between do and
done until expr2 is TRUE
Done
In above syntax BEFORE the first iteration, expr1 is evaluated. This is usually used to initialize variables for the loop.
All the statements between do and done is executed repeatedly UNTIL the value of expr2 is TRUE.
AFTER each iteration of the loop, expr3 is evaluated. This is usually use to increment a loop counter.

$ cat > for2
for (( i = 0 ; i <= 5; i++ ))
do
echo "Welcome $i times"
done

Run the above script as follows:
$ chmod +x for2
$ ./for2
Welcome 0 times
Welcome 1 times
Welcome 2 times
Welcome 3 times
Welcome 4 times
Welcome 5 times
In above example, first expression (i = 0), is used to set the value variable i to zero.
Second expression is condition i.e. all statements between do and done executed as long as expression 2 (i.e continue as
long as the value of variable i is less than or equel to 5) is TRUE.
Last expression i++ increments the value of i by 1 i.e. it's equivalent to i = i + 1 statement.



Nesting of for Loop
As you see the if statement can nested, similarly loop statement can be nested. You can nest the for loop. To understand
the nesting of for loop see the following shell script.
$ vi nestedfor.sh
for (( i = 1; i <= 5; i++ )) ### Outer for loop ###
do

for (( j = 1 ; j <= 5; j++ )) ### Inner for loop ###
do
echo -n "$i "
done

echo "" #### print the new line ###

done
$ chmod +x nestedfor.sh
$ ./nestefor.sh
11111
22222
33333
44444
55555
Here, for each value of i the inner loop is cycled through 5 times, with the varible j taking values from 1 to 5. The inner
for loop terminates when the value of j exceeds 5, and the outer loop terminets when the value of i exceeds 5.
Following script is quite intresting, it prints the chess board on screen.
$ vi chessboard
for (( i = 1; i <= 9; i++ )) ### Outer for loop ###
do
for (( j = 1 ; j <= 9; j++ )) ### Inner for loop ###
do
tot=`expr $i + $j`
tmp=`expr $tot % 2`
if [ $tmp -eq 0 ]; then
echo -e -n "033[47m "
else
echo -e -n "033[40m "
fi
done
echo -e -n "033[40m" #### set back background colour to black
echo "" #### print the new line ###
done
$ chmod +x chessboard
$ ./chessboard



On my terminal above script produec the output as follows:

Above shell script cab be explained as follows:
Command(s)/Statements Explanation
for (( i = 1; i <= 9; i++ )) Begin the outer loop which runs 9 times., and the outer
do loop terminets when the value of i exceeds 9
Begins the inner loop, for each value of i the inner loop is
for (( j = 1 ; j <= 9; j++ )) cycled through 9 times, with the varible j taking values
do from 1 to 9. The inner for loop terminates when the value
of j exceeds 9.
tot=`expr $i + $j` See for even and odd number positions using these
tmp=`expr $tot % 2` statements.
if [ $tmp -eq 0 ]; then If even number posiotion print the white colour block
echo -e -n "033[47m " (using echo -e -n "033[47m " statement); otherwise for
else odd postion print the black colour box (using echo -e -n
echo -e -n "033[40m " "033[40m " statement). This statements are responsible to
fi print entier chess board on screen with alternet colours.
done End of inner loop
Make sure its black background as we always have on our
echo -e -n "033[40m"
terminals.
echo "" Print the blank line
End of outer loop and shell scripts get terminted by printing
done
the chess board.

Exercise
Try to understand the shell scripts (for loops) shown in exercise chapter.



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Loops in Shell Scripts Up while loop


LSST v1.05r3 > Chapter 3 > The case Statement


while loop
Syntax:

while [ condition ]
do
command1
command2
command3
..
....
done
Loop is executed as long as given condition is true. For e.g.. Above for loop program (shown in last
section of for loop) can be written using while loop as:
$cat > nt1
#!/bin/sh
#
#Script to test while statement
#
#
if [ $# -eq 0 ]
then
echo "Error - Number missing form command line argument"
echo "Syntax : $0 number"
echo " Use to print multiplication table for given number"
exit 1
fi
n=$1
i=1
while [ $i -le 10 ]
do
echo "$n * $i = `expr $i * $n`"
i=`expr $i + 1`
done
Save it and try as
$ chmod 755 nt1
$./nt1 7
Above loop can be explained as follows:



Set the value of command line argument to
n=$1
variable n. (Here it's set to 7 )
i=1 Set variable i to 1
This is our loop condition, here if value of i is less
while [ $i -le 10 ] than 10 then, shell execute all statements between
do and done
do Start loop
Print multiplication table as
7*1=7
7 * 2 = 14
echo "$n * $i = `expr $i * $n`"
....
7 * 10 = 70, Here each time value of variable n is
multiply be i.
Increment i by 1 and store result to i. ( i.e. i=i+1)
Caution: If you ignore (remove) this statement
than our loop become infinite loop because value
of variable i always remain less than 10 and
i=`expr $i + 1` program will only output
7*1=7
...
...
E (infinite times)
Loop stops here if i is not less than 10 i.e.
done condition of loop is not true. Hence
loop is terminated.

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for loop Up The case Statement




The case Statement
The case statement is good alternative to Multilevel if-then-else-fi statement. It enable you to match
several values against one variable. Its easier to read and write.
Syntax:

case $variable-name in
pattern1) command
...
..
command;;
pattern2) command
...
..
command;;
patternN) command
...
..
command;;
*) command
...
..
command;;
esac
The $variable-name is compared against the patterns until a match is found. The shell then executes all
the statements up to the two semicolons that are next to each other. The default is *) and its executed if
no match is found. For e.g. write script as follows:
$ cat > car
#
# if no vehicle name is given
# i.e. -z $1 is defined and it is NULL
#
# if no command line arg
if [ -z $1 ]
then
rental="*** Unknown vehicle ***"
elif [ -n $1 ]
then
# otherwise make first arg as rental



rental=$1
fi
case $rental in
"car") echo "For $rental Rs.20 per k/m";;
"van") echo "For $rental Rs.10 per k/m";;
"jeep") echo "For $rental Rs.5 per k/m";;
"bicycle") echo "For $rental 20 paisa per k/m";;
*) echo "Sorry, I can not gat a $rental for you";;
esac
Save it by pressing CTRL+D and run it as follows:
$ chmod +x car
$ car van
$ car car
$ car Maruti-800
First script will check, that if $1(first command line argument) is given or not, if NOT given set value of
rental variable to "*** Unknown vehicle ***",if command line arg is supplied/given set value of rental
variable to given value (command line arg). The $rental is compared against the patterns until a match is
found.
For first test run its match with van and it will show output "For van Rs.10 per k/m."
For second test run it print, "For car Rs.20 per k/m".
And for last run, there is no match for Maruti-800, hence default i.e. *) is executed and it prints, "Sorry, I
can not gat a Maruti-800 for you".
Note that esac is always required to indicate end of case statement.
See the one more example of case statement in chapter 4 of section shift command.

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while loop Up How to de-bug the shell script?


LSST v1.05r3 > Chapter 3 > How to de-bug the shell script?


How to de-bug the shell script?
While programming shell sometimes you need to find the errors (bugs) in shell script and correct the
errors (remove errors - debug). For this purpose you can use -v and -x option with sh or bash command
to debug the shell script. General syntax is as follows:
Syntax:
sh option { shell-script-name }
OR
bash option { shell-script-name }
Option can be
-v Print shell input lines as they are read.
-x After expanding each simple-command, bash displays the expanded value of PS4 system variable,
followed by the command and its expanded arguments.
Example:

$ cat > dsh1.sh
#
# Script to show debug of shell
#
tot=`expr $1 + $2`
echo $tot

Press ctrl + d to save, and run it as
$ chmod 755 dsh1.sh
$ ./dsh1.sh 4 5
9
$ sh -x dsh1.sh 4 5
#
# Script to show debug of shell
#
tot=`expr $1 + $2`
expr $1 + $2
++ expr 4 + 5
+ tot=9
echo $tot
+ echo 9
9
See the above output, -x shows the exact values of variables (or statements are shown on screen with
values).


LSST v1.05r3 > Chapter 3 > How to de-bug the shell script?

$ sh -v dsh1.sh 4 5
Use -v option to debug complex shell script.

Prev Home Next
The case Statement Up Advanced Shell Scripting


LSST v1.05r3 > Chapter 4 > Introduction

Prev Chapter 4: Advanced Shell Scripting Commands Next

Introduction
After learning basis of shell scripting, its time to learn more advance features of shell scripting/command
such as:
q Functions

q User interface

q Conditional execution

q File Descriptors

q traps

q Multiple command line args handling etc

Prev Home Next
/dev/null - to send unwanted output of
How to de-bug the shell script? Up
program


LSST v1.05r3 > Chapter 4 > /dev/null - Use to send unwanted output of program


/dev/null - Use to send unwanted output
of program
This is special Linux file which is used to send any unwanted output from program/command.
Syntax:
command > /dev/null
Example:
$ ls > /dev/null
Output of above command is not shown on screen its send to this special file. The /dev directory contains
other device files. The files in this directory mostly represent peripheral devices such disks like floppy
disk, sound card, line printers etc. See the file system tutorial for more information on Linux disk,
partition and file system.
Future Point:
Run the following two commands
$ ls > /dev/null
$ rm > /dev/null
1) Why the output of last command is not redirected to /dev/null device?

Prev Home Next
Local and Global Shell variable (export
Advanced Shell Scripting Commands Up
command)


LSST v1.05r3 > Chapter 4 > Local and Global Shell variable (export comman


Local and Global Shell variable (export
command)
Normally all our variables are local. Local variable can be used in same shell, if you load another copy of
shell (by typing the /bin/bash at the $ prompt) then new shell ignored all old shell's variable. For e.g.
Consider following example
$ vech=Bus
$ echo $vech
Bus
$ /bin/bash
$ echo $vech
NOTE:-Empty line printed
$ vech=Car
$ echo $vech
Car
$ exit
$ echo $vech
Bus
Command Meaning
$ vech=Bus Create new local variable 'vech' with Bus as value in first shell
$ echo $vech Print the contains of variable vech
Now load second shell in memory (Which ignores all old shell's
$ /bin/bash
variable)
$ vech=Car Create new local variable 'vech' with Car as value in second shell
$ exit Exit from second shell return to first shell
Print the contains of variable vech (Now you can see first shells variable
$ echo $vech
and its value)

Global shell defined as:
"You can copy old shell's variable to new shell (i.e. first shells variable to seconds shell), such variable is
know as Global Shell variable."
To set global varible you have to use export command.
Syntax:
export variable1, variable2,.....variableN


LSST v1.05r3 > Chapter 4 > Local and Global Shell variable (export comman

Examples:
$ vech=Bus
$ echo $vech
Bus
$ export vech
$ /bin/bash
$ echo $vech
Bus
$ exit
$ echo $vech
Bus
Command Meaning
$ vech=Bus Create new local variable 'vech' with Bus as value in first shell
$ export
Export first shells variable to second shell i.e. global varible
vech
Now load second shell in memory (Old shell's variable is accessed from second shell,
$ /bin/bash
if they are exported )
$ exit Exit from second shell return to first shell

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/dev/null - to send unwanted output of Up Conditional execution i.e. && and ||
program


LSST v1.05r3 > Chapter 4 > Conditional execution i.e. && and ||


Conditional execution i.e. && and ||
The control operators are && (read as AND) and || (read as OR). The syntax for AND list is as follows
Syntax:
command1 && command2
command2 is executed if, and only if, command1 returns an exit status of zero.
The syntax for OR list as follows
Syntax:
command1 || command2
command2 is executed if and only if command1 returns a non-zero exit status.

You can use both as follows
Syntax:
command1 && comamnd2 if exist status is zero || command3 if exit status is non-zero
if command1 is executed successfully then shell will run command2 and if command1 is not successful
then command3 is executed.
Example:
$ rm myf && echo "File is removed successfully" || echo "File is not removed"
If file (myf) is removed successful (exist status is zero) then "echo File is removed successfully"
statement is executed, otherwise "echo File is not removed" statement is executed (since exist status is
non-zero)

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Local and Global Shell variable (export Up I/O Redirection and file descriptors
command)


LSST v1.05r3 > Chapter 4 > I/O Redirection and file descriptors


I/O Redirection and file descriptors
As you know I/O redirectors are used to send output of command to file or to read input from file.
Consider following example
$ cat > myf
This is my file
^D (press CTRL + D to save file)
Above command send output of cat command to myf file

$ cal
Above command prints calendar on screen, but if you wish to store this calendar to file then give
command
$ cal > mycal
The cal command send output to mycal file. This is called output redirection.
$ sort
10
-20
11
2
^D
-20
2
10
11
sort command takes input from keyboard and then sorts the number and prints (send) output to screen
itself. If you wish to take input from file (for sort command) give command as follows:
$ cat > nos
10
-20
11
2
^D
$ sort < nos
-20
2
10
11
First you created the file nos using cat command, then nos file given as input to sort command which
prints sorted numbers. This is called input redirection.
In Linux (And in C programming Language) your keyboard, screen etc are all treated as files. Following
are name of such files



File Descriptors
Standard File Use Example
number
as Standard
stdin 0 Keyboard
input
as Standard
stdout 1 Screen
output
as Standard
stderr 2 Screen
error

By default in Linux every program has three files associated with it, (when we start our program these
three files are automatically opened by your shell). The use of first two files (i.e. stdin and stdout) , are
already seen by us. The last file stderr (numbered as 2) is used by our program to print error on screen.
You can redirect the output from a file descriptor directly to file with following syntax
Syntax:
file-descriptor-number>filename
Examples: (Assume the file bad_file_name111 does not exists)
$ rm bad_file_name111
rm: cannot remove `bad_file_name111': No such file or directory
Above command gives error as output, since you don't have file. Now if we try to redirect this
error-output to file, it can not be send (redirect) to file, try as follows:
$ rm bad_file_name111 > er
Still it prints output on stderr as rm: cannot remove `bad_file_name111': No such file or directory, And if
you see er file as $ cat er , this file is empty, since output is send to error device and you can not redirect
it to copy this error-output to your file 'er'. To overcome this problem you have to use following
command:
$ rm bad_file_name111 2>er
Note that no space are allowed between 2 and >, The 2>er directs the standard error output to file. 2
number is default number (file descriptors number) of stderr file. To clear your idea onsider another
example by writing shell script as follows:
$ cat > demoscr
if [ $# -ne 2 ]
then
echo "Error : Number are not supplied"
echo "Usage : $0 number1 number2"
exit 1
fi
ans=`expr $1 + $2`
echo "Sum is $ans"
Run it as follows:
$ chmod 755 demoscr
$ ./demoscr
Error : Number are not supplied
Usage : ./demoscr number1 number2



$ ./demoscr > er1
$ ./demoscr 5 7
Sum is 12
For first sample run , our script prints error message indicating that you have not given two number.
For second sample run, you have redirected output of script to file er1, since it's error we have to show it
to user, It means we have to print our error message on stderr not on stdout. To overcome this problem
replace above echo statements as follows
echo "Error : Number are not supplied" 1>&2
echo "Usage : $0 number1 number2" 1>&2
Now if you run it as follows:
$ ./demoscr > er1
Error : Number are not supplied
Usage : ./demoscr number1 number2
It will print error message on stderr and not on stdout. The 1>&2 at the end of echo statement, directs the
standard output (stdout) to standard error (stderr) device.
Syntax:
from>&destination

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Conditional execution i.e. && and || Up Functions


LSST v1.05r3 > Chapter 4 > Functions


Functions
Humans are intelligent animals. They work together to perform all of life's task, in fact most of us depend
upon each other. For e.g. you rely on milkman to supply milk, or teacher to learn new technology (if
computer teacher). What all this mean is you can't perform all of life's task alone. You need somebody to
help you to solve specific task/problem.
The above logic also applies to computer program (shell script). When program gets complex we need to
use divide and conquer technique. It means whenever programs gets complicated, we divide it into small
chunks/entities which are known as functions.
Function is series of instruction/commands. Function performs particular activity in shell i.e. it had
specific work to do or simply say task. To define function use following syntax:
Syntax:
function-name ( )
{
command1
command2
.....
...
commandN
return
}
Where function-name is name of you function, that executes series of commands. A return statement will
terminate the function. Example:
Type SayHello() at $ prompt as follows
$ SayHello()
{
echo "Hello $LOGNAME, Have nice computing"
return
}
To execute this SayHello() function just type it name as follows:
$ SayHello
Hello vivek, Have nice computing.
This way you can call function. Note that after restarting your computer you will loss this SayHello()
function, since its created for current session only. To overcome this problem and to add you own
function to automate some of the day today life task, add your function to /etc/bashrc file. To add
function to this file you must logon as root. Following is the sample /etc/bashrc file with today() function
, which is used to print formatted date. First logon as root or if you already logon with your name (your
login is not root), and want to move to root account, then you can type following command , when asked



for password type root (administrators) password
$ su -l
password:
Open file /etc/bashrc using vi and goto the end of file (by pressing shift+G) and type the today()
function:
# vi /etc/bashrc
# At the end of file add following in /etc/bashrc file
#
# today() to print formatted date
#
# To run this function type today at the $ prompt
# Added by Vivek to show function in Linux
#
today()
{
echo This is a `date +"%A %d in %B of %Y (%r)"`
return
}
Save the file and exit it, after all this modification your file may look like as follows (type command cat
/etc/bashrc)
# cat /etc/bashrc
# /etc/bashrc
# System wide functions and aliases
# Environment stuff goes in /etc/profile
# For some unknown reason bash refuses to inherit
# PS1 in some circumstances that I can't figure out.
# Putting PS1 here ensures that it gets loaded every time.
PS1="[u@h W]$ "
#
# today() to print formatted date
#
# To run this function type today at the $ prompt
# Added by Vivek to show function in Linux
today()
{
echo This is a `date +"%A %d in %B of %Y (%r)"`
return
}

To run function first completely logout by typing exit at the $ prompt (Or press CTRL + D, Note you
may have to type exit (CTRL +D) twice if you login to root account by using su command) ,then login
and type $ today , this way today() is available to all user in your system, If you want to add particular



function to particular user then open .bashrc file in users home directory as follows:
# vi .bashrc
OR
# mcedit .bashrc
At the end of file add following in .bashrc file
SayBuy()
{
echo "Buy $LOGNAME ! Life never be the same, until you login again!"
echo "Press a key to logout. . ."
read
return
}
Save the file and exit it, after all this modification your file may look like as follows (type command cat
.bashrc)
# cat .bashrc
# .bashrc
#
# User specific aliases and functions
# Source global definitions
if [ -f /etc/bashrc ]; then
. /etc/bashrc
fi
SayBuy()
{
echo "Buy $LOGNAME ! Life never be the same, until you login again!"
echo "Press a key to logout. . ."
read
return
}

To run function first logout by typing exit at the $ prompt (Or press CTRL + D ) ,then logon and type $
SayBuy , this way SayBuy() is available to only in your login and not to all user in system, Use .bashrc
file in your home directory to add User specific aliases and functions only.
Tip: If you want to show some message or want to perform some action when you logout, Open file
.bash_logout in your home directory and add your stuff here For e.g. When ever I logout, I want to show
message Buy! Then open your .bash_logout file using text editor such as vi and add statement:
echo "Buy $LOGNAME, Press a key. . ."
read
Save and exit from the file. Then to test this logout from your system by pressing CTRL + D (or type
exit) immediately you will see message "Buy xxxxx, Press a key. . .", after pressing key you will be
logout and login prompt will be shown to you. :-)



Why to write function?
q Saves lot of time.
q Avoids rewriting of same code again and again
q Program is easier to write.
q Program maintains is very easy.

Passing parameters to User define function.

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I/O Redirection and file descriptors Up User Interface and dialog utility


LSST v1.05r3 > Chapter 4 > User Interface and dialog utility-Part I


User Interface and dialog utility-Part I
Good program/shell script must interact with users. You can accomplish this as follows:
(1) Use command line arguments (args) to script when you want interaction i.e. pass command line args
to script as : $ ./sutil.sh foo 4, where foo & 4 are command line args passed to shell script sutil.sh.
(2) Use statement like echo and read to read input into variable from the prompt. For e.g. Write script as:

$ cat > userinte
#
# Script to demo echo and read command for user interaction
#
echo "Your good name please :"
read na
echo "Your age please :"
read age
neyr=`expr $age + 1`
echo "Hello $na, next year you will be $neyr yrs old."

Save it and run as
$ chmod 755 userinte
$ ./userinte
Your good name please :
Vivek
Your age please :
25
Hello Vivek, next year you will be 26 yrs old.
Even you can create menus to interact with user, first show menu option, then ask user to choose menu
item, and take appropriate action according to selected menu item, this technique is show in following
script:



$ cat > menuui
#
# Script to create simple menus and take action according to that
selected
# menu item
#
while :
do
clear
echo "-------------------------------------"
echo " Main Menu "
echo "-------------------------------------"
echo "[1] Show Todays date/time"
echo "[2] Show files in current directory"
echo "[3] Show calendar"
echo "[4] Start editor to write letters"
echo "[5] Exit/Stop"
echo "======================="
echo -n "Enter your menu choice [1-5]: "
read yourch
case $yourch in
1) echo "Today is `date` , press a key. . ." ; read ;;
2) echo "Files in `pwd`" ; ls -l ; echo "Press a key. . ." ;
read ;;
3) cal ; echo "Press a key. . ." ; read ;;
4) vi ;;
5) exit 0 ;;
*) echo "Opps!!! Please select choice 1,2,3,4, or 5";
echo "Press a key. . ." ; read ;;
esac
done
Above all statement explained in following table:
Statement Explanation
Start infinite loop, this loop will
only break if you select 5 ( i.e.
while :
Exit/Stop menu item) as your menu
choice
do Start loop
Clear the screen, each and every
clear
time



echo "-------------------------------------"
echo " Main Menu "
echo "-------------------------------------"
echo "[1] Show Todays date/time"
Show menu on screen with menu
echo "[2] Show files in current directory"
items
echo "[3] Show calendar"
echo "[4] Start editor to write letters"
echo "[5] Exit/Stop"
echo "======================="
Ask user to enter menu item
echo -n "Enter your menu choice [1-5]: "
number
read yourch Read menu item number from user
case $yourch in
1) echo "Today is `date` , press a key. . ." ; read ;;
2) echo "Files in `pwd`" ; ls -l ;
Take appropriate action according
to selected menu item, If menu item
3) cal ; echo "Press a key. . ." ; read ;;
is not between 1 - 5, then show
4) vi ;;
error and ask user to input number
5) exit 0 ;;
between 1-5 again
*) echo "Opps!!! Please select choice 1,2,3,4, or 5";
esac
Stop loop , if menu item number is
done
5 ( i.e. Exit/Stop)

User interface usually includes, menus, different type of boxes like info box, message box, Input box etc.
In Linux shell (i.e. bash) there is no built-in facility available to create such user interface, But there is
one utility supplied with Red Hat Linux version 6.0 called dialog, which is used to create different type
of boxes like info box, message box, menu box, Input box etc. Next section shows you how to use dialog
utility.

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Functions Up User Interface and dialog utility-Part II


LSST v1.05r3 > Chapter 4 > User Interface and dialog utility-Part II

User Interface and dialog utility-Part II
Before programming using dialog utility you need to install the dialog utility, since dialog utility in not installed by default.
For Red Hat Linux 6.2 user install the dialog utility as follows (First insert Red Hat Linux 6.2 CD into CDROM drive)
# mount /mnt/cdrom
# cd /mnt/cdrom/RedHat/RPMS
# rpm -ivh dialog-0.6-16.i386.rpm

For Red Hat Linux 7.2 user install the dialog utility as follows (First insert Red Hat Linux 7.2 # 1 CD into CDROM drive)
# mount /mnt/cdrom
# cd /mnt/cdrom/RedHat/RPMS
# rpm -ivh dialog-0.9a-5.i386.rpm

After installation you can start to use dialog utility. Before understanding the syntax of dialog utility try the following script:
$ cat > dia1
dialog --title "Linux Dialog Utility Infobox" --backtitle "Linux Shell
Script
Tutorial" --infobox "This is dialog box called infobox, which is used

to show some information on screen, Thanks to Savio Lam and
Stuart Herbert to give us this utility. Press any key. . . " 7 50 ;
read
Save the shell script and run it as:
$ chmod +x dia1
$ ./dia1


LSST v1.05r3 > Chapter 4 > User Interface and dialog utility-Part II

After executing this dialog statement you will see box on screen with titled as "Welcome to Linux Dialog Utility" and message "This is
dialog....Press any key. . ." inside this box. The title of box is specified by --title option and infobox with --infobox "Message" with this option.
Here 7 and 50 are height-of-box and width-of-box respectively. "Linux Shell Script Tutorial" is the backtitle of dialog show on upper left side of
screen and below that line is drawn. Use dialog utility to Display dialog boxes from shell scripts.
Syntax:
dialog --title {title} --backtitle {backtitle} {Box options}
where Box options can be any one of following
--yesno {text} {height} {width}
--msgbox {text} {height} {width}
--infobox {text} {height} {width}
--inputbox {text} {height} {width} [{init}]
--textbox {file} {height} {width}
--menu {text} {height} {width} {menu} {height} {tag1} item1}...

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Message Box (msgbox) using dialog
User Interface and dialog utility-Part I Up
utility


LSST v1.05r3 > Chapter 4 > Message box (msgbox) using dialog utility

Message box (msgbox) using dialog utility
$cat > dia2
dialog --title "Linux Dialog Utility Msgbox" --backtitle "Linux Shell
Script
Tutorial" --msgbox "This is dialog box called msgbox, which is used
to show some information on screen which has also Ok button, Thanks to
Savio Lam
and Stuart Herbert to give us this utility. Press any key. . . " 9 50
Save it and run as
$ chmod +x dia2
$ ./dia2

Prev Home Next
User Interface and dialog utility-Part II Up yesno box using dialog utility


LSST v1.05r3 > Chapter 4 > yesno box using dialog utility

yesno box using dialog utility
$ cat > dia3
dialog --title "Alert : Delete File" --backtitle "Linux Shell Script
Tutorial" --yesno "nDo you want to delete '/usr/letters/jobapplication'
file" 7 60
sel=$?
case $sel in
0) echo "User select to delete file";;
1) echo "User select not to delete file";;
255) echo "Canceled by user by pressing [ESC] key";;
esac
Save the script and run it as:
$ chmod +x dia3
$ ./dia3

Above script creates yesno type dialog box, which is used to ask some questions to the user , and answer to those question either
yes or no. After asking question how do we know, whether user has press yes or no button ? The answer is exit status, if user
press yes button exit status will be zero, if user press no button exit status will be one and if user press Escape key to cancel
dialog box exit status will be one 255. That is what we have tested in our above shell script as
Statement Meaning
sel=$? Get exit status of dialog utility


LSST v1.05r3 > Chapter 4 > yesno box using dialog utility

case $sel in Now take action according to exit status
0) echo "You select to delete file";; of dialog utility, if exit status is 0 , delete
1) echo "You select not to delete file";; file, if exit status is 1 do not delete file
255) echo "Canceled by you by pressing [Escape] key";; and if exit status is 255, means Escape
esac key is pressed.

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Message Box (msgbox) using dialog utility Up Input (inputbox) using dialog utility


LSST v1.05r3 > Chapter 4 > Input Box (inputbox) using dialog utility

Input Box (inputbox) using dialog utility
$ cat > dia4
dialog --title "Inputbox - To take input from you" --backtitle "Linux
Shell
Script Tutorial" --inputbox "Enter your name please" 8 60
2>/tmp/input.$$

sel=$?

na=`cat /tmp/input.$$`
case $sel in
0) echo "Hello $na" ;;
1) echo "Cancel is Press" ;;
255) echo "[ESCAPE] key pressed" ;;
esac

rm -f /tmp/input.$$
Run it as follows:
$ chmod +x dia4
$ ./dia4

Inputbox is used to take input from user, In this example we are taking Name of user as input. But where we are going to store


LSST v1.05r3 > Chapter 4 > Input Box (inputbox) using dialog utility
inputted name, the answer is to redirect inputted name to file via statement 2>/tmp/input.$$ at the end of dialog command, which
means send screen output to file called /tmp/input.$$, letter we can retrieve this inputted name and store to variable as follows
na=`cat /tmp/input.$$`.
For input box's exit status refer the following table:
Exit Status for Input
Meaning
box
0 Command is successful
1 Cancel button is pressed by user
255 Escape key is pressed by user

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Confirmation Box (yesno box) using dialog Up
User Interface using dialog Utility -
utility Putting it all together


LSST v1.05r3 > Chapter 4 > User Interface using dialog Utility - Putting it all together

User Interface using dialog Utility - Putting it all
together
Its time to write script to create menus using dialog utility, following are menu items
Date/time
Calendar
Editor
and action for each menu-item is follows :
MENU-ITEM ACTION
Show current
Date/time
date/time
Calendar Show calendar
Editor Start vi Editor

$ cat > smenu
#
#How to create small menu using dialog
#
dialog --backtitle "Linux Shell Script Tutorial " --title "Main
Menu" --menu "Move using [UP] [DOWN],[Enter] to
Select" 15 50 3
Date/time "Shows Date and Time"
Calendar "To see calendar "
Editor "To start vi editor " 2>/tmp/menuitem.$$

menuitem=`cat /tmp/menuitem.$$`

opt=$?

case $menuitem in
Date/time) date;;
Calendar) cal;;
Editor) vi;;
esac
Save it and run as:
$ rm -f /tmp/menuitem.$$
$ chmod +x smenu
$ ./smenu


LSST v1.05r3 > Chapter 4 > User Interface using dialog Utility - Putting it all together

--menu option is used of dialog utility to create menus, menu option take
--menu options Meaning
"Move using [UP] [DOWN],[Enter] to
This is text shown before menu
Select"
15 Height of box
50 Width of box
3 Height of menu
First menu item called as tag1 (i.e. Date/time) and
Date/time "Shows Date and Time" description for menu item called as item1 (i.e. "Shows
Date and Time")
First menu item called as tag2 (i.e. Calendar) and
description for menu item called as item2 (i.e. "To see
calendar")
First menu item called as tag3 (i.e. Editor) and
Editor "To start vi editor " description for menu item called as item3 (i.e."To start
vi editor")
2>/tmp/menuitem.$$ Send selected menu item (tag) to this temporary file

After creating menus, user selects menu-item by pressing the ENTER key, selected choice is redirected to temporary file, Next
this menu-item is retrieved from temporary file and following case statement compare the menu-item and takes appropriate step
according to selected menu item. As you see, dialog utility allows more powerful user interaction then the older read and echo
statement. The only problem with dialog utility is it work slowly.

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Input (inputbox) using dialog utility Up trap command


LSST v1.05r3 > Chapter 4 > trap Command


trap command
Consider following script example:
$ cat > testsign
ls -R /
Save and run it as
$ chmod +x testsign
$ ./testsign
Now if you press ctrl + c , while running this script, script get terminated. The ctrl + c here work as
signal, When such signal occurs its send to all process currently running in your system. Now consider
following shell script:
$ cat > testsign1
#
# Why to trap signal, version 1
#
Take_input1()
{
recno=0
clear
echo "Appointment Note keeper Application for Linux"
echo -n "Enter your database file name : "
read filename
if [ ! -f $filename ]; then
echo "Sorry, $filename does not exit, Creating $filename database"
echo "Appointment Note keeper Application database file" > $filename
fi
echo "Data entry start data: `date`" >/tmp/input0.$$
#
# Set a infinite loop
#
while :
do
echo -n "Appointment Title:"
read na
echo -n "time :"
read ti
echo -n "Any Remark :"
read remark
echo -n "Is data okay (y/n) ?"



read ans
if [ $ans = y -o $ans = Y ]; then
recno=`expr $recno + 1`
echo "$recno. $na $ti $remark" >> /tmp/input0.$$
fi
echo -n "Add next appointment (y/n)?"
read isnext
if [ $isnext = n -o $isnext = N ]; then
cat /tmp/input0.$$ >> $filename
rm -f /tmp/input0.$$
return # terminate loop
fi
done
}
#
#
# Call our user define function : Take_input1
#
Take_input1
Save it and run as
$ chmod +x testsign1
$ ./testsign1
It first ask you main database file where all appointment of the day is stored, if no such database file
found, file is created, after that it open one temporary file in /tmp directory, and puts today's date in that
file. Then one infinite loop begins, which ask appointment title, time and remark, if this information is
correct its written to temporary file, After that, script asks user , whether he/she wants to add next
appointment record, if yes then next record is added , otherwise all records are copied from temporary
file to database file and then loop will be terminated. You can view your database file by using cat
command. Now problem is that while running this script, if you press CTRL + C, your shell script gets
terminated and temporary file are left in /tmp directory. For e.g. try it as follows
$./testsign1
After given database file name and after adding at least one appointment record to temporary file press
CTRL+C, Our script get terminated, and it left temporary file in /tmp directory, you can check this by
giving command as follows
$ ls /tmp/input*
Our script needs to detect such signal (event) when occurs; To achieve this we have to first detect Signal
using trap command.
Syntax:
trap {commands} {signal number list}
Signal Number When occurs
0 shell exit
1 hangup
2 interrupt (CTRL+C)



3 quit
9 kill (cannot be caught)

To catch signal in above script, put trap statement before calling Take_input1 function as trap del_file 2 .,
Here trap command called del_file() when 2 number interrupt ( i.e. CTRL+C ) occurs. Open above script
in editor and modify it so that at the end it will look like as follows:
$ vi testsign1
#
# signal is trapped to delete temporary file , version 2
#
del_file()
{
echo "* * * CTRL + C Trap Occurs (removing temporary file)* * *"
exit 1
}

Take_input1()
{
recno=0
clear
echo "Appointment Note keeper Application for Linux"
echo -n "Enter your database file name : "
read filename
if [ ! -f $filename ]; then
echo "Sorry, $filename does not exit, Creating $filename database"
echo "Appointment Note keeper Application database file" > $filename
fi
echo "Data entry start data: `date`" >/tmp/input0.$$
#
# Set a infinite loop
#
while :
do
echo -n "Appointment Title:"
read na
echo -n "time :"
read ti
echo -n "Any Remark :"
read remark
echo -n "Is data okay (y/n) ?"
read ans
if [ $ans = y -o $ans = Y ]; then
recno=`expr $recno + 1`



echo "$recno. $na $ti $remark" >> /tmp/input0.$$
fi
echo -n "Add next appointment (y/n)?"
read isnext
if [ $isnext = n -o $isnext = N ]; then
cat /tmp/input0.$$ >> $filename
return # terminate loop
fi
done # end_while
}
#
# Set trap to for CTRL+C interrupt i.e. Install our error handler
# When occurs it first calls del_file() and then exit
#
trap del_file 2
#
# Call our user define function : Take_input1
#
Take_input1
Run the script as:
$ ./testsign1
After giving database file name and after giving appointment title press CTRL+C, Here we have already
captured this CTRL + C signal (interrupt), so first our function del_file() is called, in which it gives
message as "* * * CTRL + C Trap Occurs (removing temporary file)* * * " and then it remove our
temporary file and then exit with exit status 1. Now check /tmp directory as follows
$ ls /tmp/input*
Now Shell will report no such temporary file exit.

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User Interface using dialog Utility - Putting Up The shift command
it all together


LSST v1.05r3 > Chapter 4 > The shift Command


The shift Command
The shift command moves the current values stored in the positional parameters (command line args) to
the left one position. For example, if the values of the current positional parameters are:
$1 = -f $2 = foo $3 = bar
and you executed the shift command the resulting positional parameters would be as follows:
$1 = foo $2 = bar
For e.g. Write the following shell script to clear you idea:
$ vi shiftdemo.sh
echo "Current command line args are: $1=$1, $2=$2, $3=$3"
shift
echo "After shift command the args are: $1=$1, $2=$2, $3=$3"
Excute above script as follows:
$ chmod +x shiftdemo.sh
$ ./shiftdemo -f foo bar
Current command line args are: $1=-f, $2=foo, $3=bar
After shift command the args are: $1=foo, $2=bar, $3=
You can also move the positional parameters over more than one place by specifying a number with the
shift command. The following command would shift the positional parameters two places:
shift 2

But where to use shift command?
You can use shift command to parse the command line (args) option. For example consider the following
simple shell script:



$ vi convert
while [ "$1" ]
do
if [ "$1" = "-b" ]; then
ob="$2"
case $ob in
16) basesystem="Hex";;
8) basesystem="Oct";;
2) basesystem="bin";;
*) basesystem="Unknown";;
esac
shift 2
elif [ "$1" = "-n" ]
then
num="$2"
shift 2
else
echo "Program $0 does not recognize option $1"
exit 1
fi
done
output=`echo "obase=$ob;ibase=10; $num;" | bc`
echo "$num Decimal number = $output in $basesystem number
system(base=$ob)"

Save and run the above shell script as follows:
$ chmod +x convert
$ ./convert -b 16 -n 500
500 Decimal number = 1F4 in Hex number system(base=16)
$ ./convert -b 8 -n 500
500 Decimal number = 764 in Oct number system(base=8)
$ ./convert -b 2 -n 500
500 Decimal number = 111110100 in bin number system(base=2)
$ ./convert -b 2 -v 500
Program ./convert does not recognize option -v
$ ./convert -t 2 -v 500
Program ./convert does not recognize option -t
$ ./convert -b 4 -n 500
500 Decimal number = 13310 in Unknown number system(base=4)
$ ./convert -n 500 -b 16
500 Decimal number = 1F4 in Hex number system(base=16)

Above script is run in variety of ways. First three sample run converts the number 500 ( -n 500 ) to
respectively 1F4 (hexadecimal number i.e. -b 16), 764 (octal number i.e. -b 16) , 111110100 (binary
number i.e. -b 16). It use -n and -b as command line option which means:
-b {base-system i.e. 16,8,2 to which -n number to convert}



-n {Number to convert to -b base-system}
Fourth and fifth sample run produce the error "Program ./convert does not recognize option -v". This is
because these two (-v & -t) are not the valid command line option.
Sixth sample run produced output "500 Decimal number = 13310 in Unknown number system(base=4)".
Because the base system 4 is unknown to our script.
Last sample run shows that command line options can given different ways i.e. you can use it as follows:
$ ./convert -n 500 -b 16
Instead of
$ ./convert -b 16 -n 500
All the shell script command can be explained as follows:
Command(s)/Statements Explanation
Begins the while loop; continue
while [ "$1" ]
the while loop as long as script
do
reads the all command line option
Now start to parse the command
line (args) option using if
command our script understands
the -b and -n options only all
if [ "$1" = "-b" ]; then
other option are invalid. If option
ob="$2"
is -b then stores the value of
second command line arg to
variable ob (i.e. if arg is -b 16
then store the 16 to ob)
For easy understanding of
case $ob in conversion we store the
16) basesystem="Hex";; respective number base systems
8) basesystem="Oct";; corresponding string to
2) basesystem="bin";; basesystem variable. If base
*) basesystem="Unknown";; system is 16 then store the Hex to
esac basesystem and so on. This is
done using case statement.
Once first two command line
options (args) are read, we need
shift 2 next two command line option
(args). shift 2 will moves the
current values stored in the
positional parameters (command
line args) to the left two position.



Now check the next command
line option and if its -n option
then stores the value of second
elif [ "$1" = "-n" ]
command line arg to variable
then
num (i.e. if arg is -n 500 then
num="$2"
store the 500 to num) and shift 2
shift 2
will moves the current values
stored in the positional
parameters (command line args)
to the left two position.
If command line option is not -n
else or -b then print the error
echo "Program $0 does not recognize option $1" "Program ./convert does not
exit 1 recognize option xx" on screen
fi and terminates the shell script
using exit 1 statement.
End of loop as we read all the
done
valid command line option/args.
Now convert the given number to
output=`echo "obase=$ob;ibase=10; $num;" | BC`
given number system using BC
echo "$num Decimal number = $output in $basesystem number
Show the converted number on
system(base=$ob)"
screen.

As you can see shift command can use to parse the command line (args) option. This is useful if you
have limited number of command line option. If command line options are too many then this approach
works slowly as well as complex to write and maintained. You need to use another shell built in
command - getopts. Next section shows the use of getopts command. You still need the shift command in
conjunction with getopts for other shell scripting work.

Prev Home Next
trap command Up getopts command


LSST v1.05r3 > Chapter 4 > getopts command


getopts command
This command is used to check valid command line argument are passed to script. Usually used in while
loop.
Syntax:
getopts {optstring} {variable1}

getopts is used by shell to parse command line argument.
As defined in man pages:
"optstring contains the option letters to be recognized; if a letter is followed by a colon, the option is
expected to have an argument, which should be separated from it by white space. Each time it is invoked,
getopts places the next option in the shell variable variable1, When an option requires an argument,
getopts places that argument into the variable OPTARG. On errors getopts diagnostic messages are
printed when illegal options or missing option arguments are encountered. If an illegal option is seen,
getopts places ? into variable1."

Examlpe:
We have script called ani which has syntax as
ani -n -a -s -w -d
Options: These are optional argument
-n name of animal
-a age of animal
-s sex of animal
-w weight of animal
-d demo values (if any of the above options are used their values are not taken)
Above ani script is as follows:
$ vi ani
#
# Usage: ani -n -a -s -w -d
#
#
# help_ani() To print help
#
help_ani()
{
echo "Usage: $0 -n -a -s -w -d"
echo "Options: These are optional argument"
echo " -n name of animal"
echo " -a age of animal"
echo " -s sex of animal "



echo " -w weight of animal"
echo " -d demo values (if any of the above options are used "
echo " their values are not taken)"
exit 1
}
#
#Start main procedure
#
#
#Set default value for variable
#
isdef=0
na=Moti
age="2 Months" # may be 60 days, as U like it!
sex=Male
weight=3Kg
#
#if no argument
#
if [ $# -lt 1 ]; then
help_ani
fi
while getopts n:a:s:w:d opt
do
case "$opt" in
n) na="$OPTARG";;
a) age="$OPTARG";;
s) sex="$OPTARG";;
w) weight="$OPTARG";;
d) isdef=1;;
?) help_ani;;
esac
done
if [ $isdef -eq 0 ]
then
echo "Animal Name: $na, Age: $age, Sex: $sex, Weight: $weight (user
define mode)"
else
na="Pluto Dog"
age=3
sex=Male
weight=20kg
echo "Animal Name: $na, Age: $age, Sex: $sex, Weight: $weight (demo
mode)"
fi



Save it and run as follows
$ chmod +x ani
$ ani -n Lassie -a 4 -s Female -w 20Kg
$ ani -a 4 -s Female -n Lassie -w 20Kg
$ ani -n Lassie -s Female -w 20Kg -a 4
$ ani -w 20Kg -s Female -n Lassie -a 4
$ ani -w 20Kg -s Female
$ ani -n Lassie -a 4
$ ani -n Lassie
$ ani -a 2

See because of getopts, we can pass command line argument in different style. Following are invalid
options for ani script
$ ani -nLassie -a4 -sFemal -w20Kg
No space between option and their value.
$ ani -nLassie-a4-sFemal-w20Kg
$ ani -n Lassie -a 4 -s Female -w 20Kg -c Mammal
-c is not one of the valid options.

Prev Home Next
The shift command Up Essential Utilities for Power User


LSST v1.05r3 > Chapter 5 > Introduction

Prev Chapter 5: Essential Utilities for Power User Next

Introduction
Linux contains powerful utility programs. You can use these utility to
q Locate system information

q For better file management

q To organize your data

q System administration etc

Following section introduce you to some of the essential utilities as well as expression. While
programming shell you need to use these essential utilities. Some of these utilities (especially sed & awk)
requires understanding of expression. After the quick introduction to utilities, you will learn the
expression.

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Preparing for Quick Tour of essential
getopts command Up
utilities


LSST v1.05r3 > Chapter 5 > Prepering for Quick Tour of essential utilities


Prepering for Quick Tour of essential
utilities
For this part of tutorial create sname and smark data files as follows (Using text editor of your choice)
Note Each data block is separated from the other by TAB character i.e. while creating the file if you type
11 then press "tab" key, and then write Vivek (as shown in following files):
sname

Sr.No Name
11 Vivek
12 Renuka
13 Prakash
14 Ashish
15 Rani
smark

Sr.No Mark
11 67
12 55
13 96
14 36
15 67

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Essential Utilities for Power User Up Selecting portion of a file using cut utility


LSST v1.05r3 > Chapter 5 > Selecting portion of a file using cut utility


Selecting portion of a file using cut utility
Suppose from sname file you wish to print name of student on-screen, then from shell (Your command
prompt i.e. $) issue command as follows:
$cut -f2 sname
Vivek
Renuka
Prakash
Ashish
Rani

cut utility cuts out selected data from sname file. To select Sr.no. field from sname give command as
follows:
$cut -f1 sname
11
12
13
14
15
Command Explanation
cut Name of cut utility
Using (-f) option, you are specifying the extraction field number. (In this example
-f1
its 1 i.e. first field)
sname File which is used by cut utility and which is use as input for cut utility.

You can redirect output of cut utility as follows
$cut -f2 sname > /tmp/sn.tmp.$$
$cut -f2 smark > /tmp/sm.tmp.$$
$cat /tmp/sn.tmp.$$
Vivek
Renuka
Prakash
Ashish
Rani
$cat /tmp/sm.tmp.$$
67
55
96
36
67


LSST v1.05r3 > Chapter 5 > Selecting portion of a file using cut utility

General Syntax of cut utility:
Syntax:
cut -f{field number} {file-name}
Use of Cut utility:
Selecting portion of a file.

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Preparing for Quick Tour of essential Up Putting lines together using paste utility
utilities


LSST v1.05r3 > Chapter 5 > Putting lines together using paste utility


Putting lines together using paste utility
Now enter following command at shell prompt
$ paste sname smark
11 Vivek 11 67
12 Renuka 12 55
13 Prakash 13 96
14 Ashish 14 36
15 Rani 15 67
Paste utility join textual information together. To clear your idea try following command at shell prompt:

$ paste /tmp/sn.tmp.$$ /tmp/sm.tmp.$$
Vivek 67
Renuka 55
Prakash 96
Ashish 36
Rani 67
Paste utility is useful to put textual information together located in various files.
General Syntax of paste utility:
Syntax:
paste {file1} {file2}
Use of paste utility:
Putting lines together.
Can you note down basic difference between cut and paste utility?

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Selecting portion of a file using cut utility Up The join utility


LSST v1.05r3 > Chapter 5 > The join utility


The join utility
Now enter following command at shell prompt:
$join sname smark
11 Vivek 67
12 Renuka 55
13 Prakash 96
14 Ashish 36
15 Rani 67
Here students names are matched with their appropriate marks. How ? join utility uses the Sr.No. field to
join to files. Notice that Sr.No. is the first field in both sname and smark file.
General Syntax of join utility:
Syntax:
join {file1} {file2}
Use of join utility:
The join utility joins, lines from separate files.
Note that join will only work, if there is common field in both file and if values are identical to each
other.

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Translating range of characters using tr
Putting lines together using paste utility Up
utility


LSST v1.05r3 > Chapter 5 > Translateing range of characters using tr utility


Translateing range of characters using tr
utility
Type the following command at shell prompt:
$ tr "h2" "3x" < sname
11 Vivek
1x Renuka
13 Prakas3
14 As3is3
15 Rani
You can clearly see that each occurrence of character 'h' is replace with '3' and '2' with 'x'. tr utility
translate specific characters into other specific characters or range of characters into other ranges.
h -> 3
2 -> x
Consider following example: (after executing command type text in lower case)
$ tr "[a-z]" "[A-Z]"
hi i am Vivek
HI I AM VIVEK
what a magic
WHAT A MAGIC
{Press CTRL + C to terminate.}
Here tr translate range of characters (i.e. small a to z) into other (i.e. to Capital A to Z) ranges.
General Syntax & use of tr utility:
Syntax:
tr {pattern-1} {pattern-2}
Use of tr utility:
To translate range of characters into other range of characters.
After typing following paragraph, I came to know my mistake that entire paragraph must be in lowercase
characters, how to correct this mistake? (Hint - Use tr utility)

$ cat > lcommunity.txt
THIS IS SAMPLE PARAGRAPH
WRITTEN FOR LINUX COMMUNITY,
BY VIVEK G GITE (WHO ELSE?)
OKAY THAT IS OLD STORY.


LSST v1.05r3 > Chapter 5 > Translateing range of characters using tr utility

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The join utility Up Data manipulation using awk utility


LSST v1.05r3 > Chapter 5 > Data manipulation using awk utility


Data manipulation using awk utility
Before learning more about awk create data file using any text editor or simply vi:
inventory

egg order 4
cacke good 10
cheese okay 4
pen good 12
floppy good 5
After crating file issue command
$ awk '/good/ { print $3 }' inventory
10
12
5
awk utility, select each record from file containing the word "good" and performs the action of printing
the third field (Quantity of available goods.). Now try the following and note down its output.
$ awk '/good/ { print $1 " " $3 }' inventory
General Syntax of awk utility:
Syntax:
awk 'pattern action' {file-name}
For $ awk '/good/ { print $3 }' inventory example,
/good/ Is the pattern used for selecting lines from file.
{print This is the action; if pattern found, print on of such action. Here $3 means third record in
$3} selected record. (What $1 and $2 mean?)
inventory File which is used by awk utility which is use as input for awk utility.

Use of awk utility:
To manipulate data.

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Translating range of characters using tr Up sed utility - Editing file without using
utility editor


LSST v1.05r3 > Chapter 5 > sed utility - Editing file without using editor


sed utility - Editing file without using
editor
For this part of tutorial create data file as follows
teaormilk

India's milk is good.
tea Red-Lable is good.
tea is better than the coffee.
After creating file give command
$ sed '/tea/s//milk/g' teaormilk > /tmp/result.tmp.$$
$ cat /tmp/result.tmp.$$
milk Red-Lable is good.
milk is better than the coffee.
sed utility is used to find every occurrence of tea and replace it with word milk. sed - Steam line editor
which uses 'ex' editors command for editing text files without starting ex. (Cool!, isn't it? no use of text
editor to edit anything!!!)
Find tea word or select all lines having the
/tea/
word tea
Replace (substitute) the word milk for the
s//milk/
tea.
g Make the changes globally.

Syntax:
sed {expression} {file}
Use of sed utility: sed is used to edit (text transformation) on given stream i.e a file or may be input from
a pipeline.

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Removing duplicate lines using uniq
Data manipulation using awk utility Up
utility


LSST v1.05r3 > Chapter 5 > Removing duplicate lines using uniq utility


Removing duplicate lines using uniq
utility
Create text file personame as follows:
personame

Hello I am vivek
12333
12333
welcome
to
sai computer academy, a'bad.
what still I remeber that name.
oaky! how are u luser?

After creating file, issue following command at shell prompt
$ uniq personame
Hello I am vivek
12333
welcome
to
Above command prints those lines which are unique. For e.g. our original file contains 12333 twice, so
additional copies of 12333 are deleted. But if you examine output of uniq, you will notice that 12333 is
gone (Duplicate), and "what still I remeber that name" remains as its. Because the uniq utility compare
only adjacent lines, duplicate lines must be next to each other in the file. To solve this problem you can
use command as follows
$ sort personame | uniq
General Syntax of uniq utility:
Syntax:
uniq {file-name}


LSST v1.05r3 > Chapter 5 > Removing duplicate lines using uniq utility

Prev Home Next
sed utility - Editing file without using Up Finding matching pattern using grep
editor utility


LSST v1.05r3 > Chapter 5 > Finding matching pattern using grep utility


Finding matching pattern using grep
utility
Create text file as follows:
demo-file

hello world!
cartoons are good
especially toon like tom (cat)
what
the number one song
12221
they love us
I too
After saving file, issue following command,
$ grep "too" demofile
cartoons are good
I too
grep will locate all lines for the "too" pattern and print all (matched) such line on-screen. grep prints too,
as well as cartoons and toon; because grep treat "too" as expression. Expression by grep is read as the
letter t followed by o and so on. So if this expression is found any where on line its printed. grep don't
understand words.
Syntax:
grep "word-to-find" {file-name}

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Removing duplicate lines from text Up Learning expressions with ex
database file using uniq utility


LSST v1.05 > Chapter 6 > Introduction

Prev Chapter 6: Learning expressions with ex Next

Introduction
In the chpater 5, "Quick Tour of essential utilities", you have seen basic utilities. If you use them with
other tools, these utilities are very useful for data processing or for other works. In rest part of tutorial we
will learn more about patterns, filters, expressions, and off course sed and awk in depth.

Learning expressions with ex
What does "cat" mean to you ?
One its the word cat, (second cat is an animal! I know 'tom' cat), If same question is asked to computer
(not computer but to grep utility) then grep will try to find all occurrence of "cat" word (remember grep
read word "cat" as the c letter followed by a and followed by t) including cat, copycat, catalog etc.
Pattern defined as:
"Set of characters (may be words or not) is called pattern."
For e.g. "dog", "celeron", "mouse", "ship" etc are all example of pattern. Pattern can be change from one
to another, for e.g. "ship" as "sheep".
Metacharacters defined as:
"If patterns are identified using special characters then such special characters are known as
metacharacters".
expressions defined as:
"Combination of pattern and metacharacters is known as expressions (regular expressions)."
Regular expressions are used by different Linux utilities like
q grep

q awk

q sed

So you must know how to construct regular expression. In the next part of LSST you will learn how to
construct regular expression using ex editor.
For this part of chapter/tutorial create 'demofile' - text file using any text editor.

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Finding matching pattern using grep utility Up Getting started with ex


LSST v1.05 > Chapter 6 > Getting started with ex


Getting started with ex
You can start the ex editor by typeing ex at shell prompt:
Syntax:
ex {file-name}

Example:
$ ex demofile
The : (colon) is ex prompt where you can type ex text editor command or regular expression. Its time to
open our demofile, use ex as follows:
$ ex demofile
"demofile" [noeol] 20L, 387C
Entering Ex mode. Type "visual" to go to Normal mode.
:
As you can see, you will get : prompt, here you can type ex command, type q and press ENTER key to
exit from ex as shown follows: (remember commands are case sensetive)
:q
vivek@ls vivek]$
After typing the q command you are exit to shell prompt.

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Learning expressions with ex Up Printing text on-screen


LSST v1.05 > Chapter 6 > Printing text on-screen


Printing text on-screen
First open the our demofile as follows:
$ ex demofile
"demofile" [noeol] 20L, 387C
Entering Ex mode. Type "visual" to go to Normal mode.
Now type 'p' in front of : as follow and press enter
:p
Okay! I will stop.
:
NOTE By default p command will print current line, in our case its the last line of above text file.

Printing lines using range
Now if you want to print 1st line to next 5 line (i.e. 1 to 5 lines) then give command
:1,5 p
Hello World.
This is vivek from Poona.
I love linux.
It is different from all other Os
NOTE Here 1,5 is the address. if single number is used (e.g. 5 p) it indicate line number and if two
numbers are separated by comma its range of line.

Printing particular line
To print 2nd line from our file give command
:2 p

Printing entire file on-screen
Give command
:1,$ p
Hello World.
I love linux.


LSST v1.05 > Chapter 6 > Printing text on-screen

.....
...
.....
Okay! I will stop.
NOTE Here 1 is 1st line and $ is the special character of ex which mean last-line character. So 1,$ means
print from 1st line to last-line character (i.e. end of file). Here p stands print.

Printing line number with our text
Give command
:set number
:1,3 p
1 Hello World.
2 This is vivek from Poona.
3
NOTE This command prints number next to each line. If you don't want number you can turn off
numbers by issuing following command
:set nonumber
:1,3 p
Hello World.

Prev Home Next
Getting started with ex Up Deleting lines


LSST v1.05 > Chapter 6 > Deleting lines


Deleting lines
Give command
:1, d
I love linux.
NOTE
Here 1 is 1st line and d command indicates deletes (Which deletes the 1st line).
You can even delete range of line by giving command as
:1,5 d

Prev Home Next
Printing text on-screen Up Copying lines


LSST v1.05 > Chapter 6 > Copying lines


Copying lines
Give command as follows
:1,4 co $
:1,$ p
I love linux.
....
.....
. (DOT) is special command of linux.
Okay! I will stop.
I love linux.
My brother Vikrant also loves linux.
NOTE Here 1,4 means copy 1 to 4 lines; co command stands for copy; $ is end of file. So it mean copy
first four line to end of file. You can delete this line as follows
:18,21 d
Okay! I will stop.
:1,$ p
I love linux.
He currently lerarns linux.
Linux is cooool.
Linux is now 10 years old.
Next year linux will be 11 year old.
Rani my sister never uses Linux
She only loves to play games and nothing else.
Do you know?


LSST v1.05 > Chapter 6 > Copying lines

Okay! I will stop.

Prev Home Next
Deleting lines Up Searching the words


LSST v1.05 > Chapter 6 > Searching the words


Searching the words
(a) Give following command
:/linux/ p
I love linux.
Note In ex you can specify address (line) using number for various operation. This is useful if you know
the line number in advance, but if you don't know line number, then you can use contextual address to
print line on-screen. In above example /linux/ is contextual address which is constructed by surrounding
a regular expression with two slashes. And p is print command of ex.
Try following and note down difference (Hint - Watch p is missing)
:/Linux/
(b)Give following command
:g/linux/ p
I love linux.
In previous example (:/linux/ p) only one line is printed. If you want to print all occurrence of the word
"linux" then you have to use g, which mean global line address. This instruct ex to find all occurrence of
pattern. Try following
:1,$ /Linux/ p
Which give the same result. It means g stands for 1,$.

Saving the file in ex
Give command
:w
"demofile" 20L, 386C written
w command will save the file.

Quitting the ex
Give command
:q


LSST v1.05 > Chapter 6 > Searching the words

q command quits from ex and you are return to shell prompt.
Note use wq command to do save and exit from ex.

Prev Home Next
Find and Replace (Substituting regular
Coping lines Up
expression)


LSST v1.05 > Chapter 6 > Find and Replace (Substituting regular expression)


Find and Replace (Substituting regular
expression)
:8 p
:8 s/lerarns/learn/
:p
He currently learn linux.
Note Using above command, you are substituting the word "learn" for the word "lerarns".
Above command can be explained as follows:
Command Explanation
8 Goto line 8, address of line.
s Substitute
/lerarns/ Target pattern
If target pattern found substitute the expression (i.e.
learn/
learn/ )

Considered the following command:
:1,$ s/Linux/Unix/
Rani my sister never uses Unix
:1,$ p
Hello World.
....
..
.....
Okay! I will stop.
Using above command, you are substituting all lines i.e. s command will find all of the address line for
the pattern "Linux" and if pattern "Linux" found substitute pattern "Unix".
Command Explanation
:1,$ Substitute for all line
s Substitute



/Linux/ Target pattern
If target pattern found substitute the expression
Unix/
(i.e. Unix/ )

Even you can also use contextual address as follows
:/sister/ p
Rani my sister never uses Unix
:g /sister/ s/never/always/
:p
Rani my sister always uses Unix
Above command will first find the line containing pattern "sister" if found then it will substitute the
pattern "always" for the pattern "never" (It mean find the line containing the word sister, on that line find
the word never and replace it with word always.)
Try the following and watch the output very carefully.
:g /Unix/ s/Unix/Linux
3 substitutions on 3 lines
Above command finds all line containing the regular expression "Unix", then substitute "Linux" for all
occurrences of "Unix". Note that above command can be also written as follows
:g /Unix/ s//Linux
Here // is replace by the last pattern/regular expression i.e. Unix. Its shortcut. Now try the following
:g /Linux/ s//UNIX/
:g/Linux/p
Linux is cooool.
Rani my sister always uses Linux
:g /Linux/ s//UNIX/
:g/UNIX/p
UNIX is cooool.
UNIX is now 10 years old.
Rani my sister always uses UNIX
By default substitute command only substitute first occurrence of a pattern on a line. Let's take another
example, give command
:/brother/p
My brother Vikrant also loves linux who also loves unix.
Now in above line "also" word is occurred twice, give the following substitute command
:g/brother/ s/also/XYZ/
:/brother/p
My brother Vikrant XYZ loves linux who also loves unix.



Make sure next time it works
:g/brother/ s/XYZ/also/
Note that "also" is only once substituted. If you want to s command to work with all occurrences of
pattern within a address line give command as follows:
:g/brother/ s/also/XYZ/g
:p
My brother Vikrant XYZ loves linux who XYZ loves unix.
:g/brother/ s/XYZ/also/g
:p
The g option at the end instruct s command to perform replacement on all occurrences of the target
pattern within a address line.

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Replacing word with confirmation from
Searching the words Up
user


LSST v1.05 > Chapter 6 > Replacing word with confirmation from user


Replacing word with confirmation from
user
:g/Linux/ s//UNIX/gc
After giving this command ex will ask you question like - replace with UNIX (y/n/a/q/^E/^Y)?
Type y to replace the word or n to not replace or a to replace all occurrence of word.

Prev Home Next
Find and Replace (Substituting regular Up Finding words
expression)


LSST v1.05 > Chapter 6 > Finding words


Finding words
Command like
:g/the/p
Will find word like theater, the, brother, other etc. What if you want to just find the word like "the" ? To
find the word (Let's say Linux) you can give command like
:/<Linux>
Linux is cooool.
:g/<Linux>/p
Linux is cooool.
The symbol < and > respectively match the empty string at the beginning and end of the word. To find
the line which contain Linux pattern at the beginning give command
:/^Linux
Linux is cooool.
As you know $ is end of line character, the ^ (caret) match beginning of line. To find all occurrence of
pattern "Linux" at the beginning of line give command
:g/^Linux
Linux is cooool.
And if you want to find "Linux" at the end of line then give command
:/Linux $
Following command will find empty line:
:/^$
To find all blank line give command:
:g/^$
To view entire file without blank line you can use command as follows:
:g/[^/^$]
Hello World.
I love linux.



Linux is cooool.
Do you know?
Okay! I will stop.
Command Explanation
g All occurrence
/[^ [^] This means not
Empty line, Combination of ^
/^$
and $.

To delete all blank line you can give command as follows
:g/^$/d
Okay! I will stop.
:1,$ p
Hello World.
I love linux.
Linux is cooool.
Do you know?
Okay! I will stop.
Try u command to undo, to undo what you have done it, give it as follows:
:u
:1,$ p
Hello World.
....
...
....
Okay! I will stop.



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Replacing word with confirmation from Up Using range of characters in regular
user expressions


LSST v1.05 > Chapter 6 > Using range of characters in regular expressions


Using range of characters in regular
expressions
Try the following command
:g/Linux/p
Linux is cooool.
This will find only "Linux" and not the "linux", to overcome this problem try as follows
:g/[Ll]inux/p
I love linux.
Linux is cooool.
Here a list of characters enclosed by [ and ], which matches any single character in that range. if the first
character of list is ^, then it matches any character not in the list. In above example [Ll], will try to match
L or l with rest of pattern. Let's see another example. Suppose you want to match single digit character in
range you can give command as follows
:/[0123456789]
Even you can try it as follows
:g/[0-9]
Here range of digit is specified by giving first digit (0-zero) and last digit (1), separated by hyphen. You
can try [a-z] for lowercase character, [A-Z] for uppercase character. Not just this, there are certain named
classes of characters which are predefined. They are as follows:
Predefined
classes of Meaning
characters
[:alnum:] Letters and Digits (A to Z or a to z or 0 to 9)
[:alpha:] Letters A to Z or a to z
[:cntrl:] Delete character or ordinary control character (0x7F or 0x00 to 0x1F)



[:digit:] Digit (0 to 9)
[:graph:] Printing character, like print, except that a space character is excluded
[:lower:] Lowercase letter (a to z)
[:print:] Printing character (0x20 to 0x7E)
[:punct:] Punctuation character (ctrl or space)
Space, tab, carriage return, new line, vertical tab, or form feed (0x09
[:space:]
to 0x0D, 0x20)
[:upper:] Uppercase letter (A to Z)
[:xdigit:] Hexadecimal digit (0 to 9, A to F, a to f)

For e.g. To find digit or alphabet (Upper as well as lower) you will write
:/[0-9A-Za-Z]
Instead of writing such command you could easily use predefined classes or range as follows
:/[[:alnum:]]
The . (dot) matches any single character.
For e.g. Type following command
:g/<.o>
Do you know?
This will include lo(ves), Do, no(thing) etc.
* Matches the zero or more times
For e.g. Type following command
:g/L*
Hello World.
....
....
:g/Li*
Linux is cooool.
:g/c.*and
Here first c character is matched, then any single character (.) followed by n number of single character
(1 or 100 times even) and finally ends with and. This can found different word as follows command or
catand etc.
In the regular expression metacharacters such as . (DOT) or * loose their special meaning if we use as .
or *. The backslash removes the special meaning of such meatcharacters and you can use them as
ordinary characters. For e.g. If u want to search . (DOT) character at the beginning of line, then you can't



use command as follows
:g/^.
Hello World.
....
..
...
Okay! I will stop.
Instead of that use
:g/^.

Prev Home Next
Finding words Up Using & as Special replacement character


LSST v1.05 > Chapter 6 > Using & as Special replacement characte


Using & as Special replacement
character
Try the following command:
:1,$ s/Linux/&-Unix/p
Rani my sister never uses Linux-Unix
:g/Linux-Unix/p
Linux-Unix is cooool.
Linux-Unix is now 10 years old.
Rani my sister never uses Linux-Unix
This command will replace, target pattern "Linux" with "Linux-Unix". & before - Unix means use "last
pattern found" with given pattern, So here last pattern found is "Linux" which is used with given -Unix
pattern (Finally constructing "Linux-Unix" substitute for "Linux").
Can you guess the output of this command?
:1,$ s/Linux-Unix/&Linux/p

Prev Home Next
Using range of characters in regular Up Converting lowercase character to
expressions uppercase


LSST v1.05 > Chapter 6 > Converting lowercase character to uppercase


Converting lowercase character to
uppercase
Try the following command
:1,$ s/[a-z]/u &/g
Above command can be explained as follows:
Command Explanation
1,$ Line Address location is all i.e. find all lines for following pattern
s Substitute command
/[a-z]/ Find all lowercase letter - Target
Substitute to Uppercase. u& means substitute last patter (&) matched with its
u&/
UPPERCASE replacement (u) Note: Use l (small L) for lowercase character.
g Global replacement

Can you guess the output of following command?
:1,$ s/[A-Z]/l&/g

Congratulation, for successfully completion of this tutorial of regular expressions.
I hope so you have learn lot from this. To master the expression you have to do lot of practice. This
tutorial is very important to continue with rest of tutorial and to become power user of Linux. Impress
your friends with such expressions. Can you guess what last expression do?
:1,$ s/^ *$//
Note : indicates two black space.

Prev Home Next
Using & as Special replacement character Up awk - Revisited


LSST v1.05 > Chapter 7 > awk - Revisited

Prev Chapter 7: awk Revisited Next

Introduction : awk - Revisited
awk utility is powerful data manipulation/scripting programming language (In fact based on the C
programming Language). Use awk to handle complex task such as calculation, database handling, report
creation etc.
General Syntax of awk:
Syntax:
awk -f {awk program file} filename
awk Program contains are something as follows:
Pattern {
action 1
action 2
action N
}
awk reads the input from given file (or from stdin also) one line at a time, then each line is compared
with pattern. If pattern is match for each line then given action is taken. Pattern can be regular
expressions. Following is the summery of common awk metacharacters:
Metacharacter Meaning
. (Dot) Match any character
* Match zero or more character
^ Match beginning of line
$ Match end of line
Escape character following
[] List
{} Match range of instance
+ Match one more preceding
? Match zero or one preceding
| Separate choices to match

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Converting lowercase character to Up Getting Starting with awk
uppercase


LSST v1.05 > Chapter 7 >


Getting Starting with awk
Consider following text database file
Unit
Sr.No Product Qty
Price
1 Pen 5 20.00
2 Rubber 10 2.00
3 Pencil 3 3.50
4 Cock 2 45.50

In above file fields are Sr.No,Product,Qty,Unit Price. Field is the smallest element of any record. Each
fields has its own attributes. For e.g. Take Qty. field. Qty. fields attribute is its numerical (Can contain
only numerical data). Collection of fields is know as record. So
1. Pen 5 20.00 ----> Is a Record.
Collection of record is know as database file. In above text database file each field is separated using
space (or tab character) and record is separated using new-line character ( i.e. each record is finished at
the end of line ). In the awk, fields are access using special variable. For e.g. In above database $1, $2,
$3, $4 respectively represents Sr.No, Product, Qty, Unit Price fields. (Don't confuse $1,$2 etc with
command line arguments of shell script)
For this part of tutorial create text datafile inven (Shown as above). Now enter following simple awk
program/command at shell prompt:
$ awk '{ print $1 $2 "--> Rs." $3 * $4 }' inven
1.Pen--> Rs.100
2.Pencil--> Rs.20
3.Rubber--> Rs.10.5
4.Cock--> Rs.91
Above awk program/command can be explained as follows:
awk program statement Explanation
print command is used to print contains of variables or text enclose in
" text ". Here $1, $2, $3,$4 are all the special variable. $1, $2, etc all
'{ print $1 $2 "--> Rs." $3 * $4
of the variable contains value of field. Finally we can directly do the
}'
calculation using $3 * $4 i.e. multiplication of third and fourth field in
database. Note that "--> Rs." is string which is printed as its.

Note $1,$2 etc (in awk) also know as predefined variable and can assign any value found in field.
Type following awk program at shell prompt,



$ awk '{ print $2 }' inven
Pen
Pencil
Rubber
Cock
awk prints second field from file. Same way if you want to print second and fourth field from file then
give following command:
$awk '{ print $2 $4}' inven
Pen20.00
Pencil2.00
Rubber3.50
Cock45.50
$0 is special variable of awk , which print entire record, you can verify this by issuing following awk
command:
$ awk '{ print $0 }' inven
1. Pen 5 20.00
2. Pencil 10 2.00
3. Rubber 3 3.50
4. Cock 2 45.50
You can also create awk command (program) file as follows:
$ cat > prn_pen
/Pen/ { print $3 }
And then you can execute or run above "prn_pen" awk command file as follows
$ awk -f prn_pen inven
5
10

In above awk program /Pen/ is the search pattern, if this pattern is found on line (or record) then print the
third field of record.
{ print $3 } is called Action. On shell prompt , $ awk -f prn_pen inven , -f option instruct awk, to read its
command from given file, inven is the name of database file which is taken as input for awk.
Now create following awk program as follows:
$cat > comp_inv
3 > 5 { print $0 }
Run it as follows:
$ awk -f comp_inv inven
2. Pencil 10 2.00
Here third field of database is compared with 5, this the pattern. If this pattern found on any line
database, then entire record is printed.



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awk Revisited Up Predefined variable of awk


LSST v1.05 > Chapter 7 > Predefined variable of awk


Predefined variable of awk
Our next example talks more about predefined variable of awk. Create awk file as follows:

$cat > def_var
{
print "Printing Rec. #" NR "(" $0 "),And # of field for this record is
" NF
}
Run it as follows.
$awk -f def_var inven
Printing Rec. #1(1. Pen 5 20.00),And # of field for this record is 4
Printing Rec. #2(2. Pencil 10 2.00),And # of field for this record is 4
Printing Rec. #3(3. Rubber 3 3.50),And # of field for this record is 4
Printing Rec. #4(4. Cock 2 45.50),And # of field for this record is 4
NR and NF are predefined variables of awk which means Number of input Record, Number of Fields in
input record respectively. In above example NR is changed as our input record changes, and NF is
constant as there are only 4 field per record. Following table shows list of such built in awk variables.
awk Variable Meaning
FILENAME Name of current input file
Input record separator character (Default is
RS
new line)
Output field separator string (Blank is
OFS
default)
Output record separator string (Default is
ORS
new line)
NF Number of input record
NR Number of fields in input record
OFMT Output format of number
Field separator character (Blank & tab is
FS
default)

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Getting Starting with awk Up Doing arithmetic with awk


LSST v1.05 > Chapter 7 > Doing arithmetic with awk


Doing arithmetic with awk
You can easily, do the arithmetic with awk as follows
$ cat > math
{
print $1 " + " $2 " = " $1 + $2
print $1 " - " $2 " = " $1 - $2
print $1 " / " $2 " = " $1 / $2
print $1 " x " $2 " = " $1 * $2
print $1 " mod " $2 " = " $1 % $2
}
Run the awk program as follows:
$ awk -f math
20 3
20 + 3 = 23
20 - 3 = 17
20 / 3 = 6.66667
20 x 3 = 60
20 mod 3 = 2
(Press CTRL + D to terminate)
In above program print $1 " + " $2 " = " $1 + $2, statement is used for addition purpose. Here $1 + $2,
means add (+) first field with second field. Same way you can do - (subtraction ), * (Multiplication), /
(Division), % (modular use to find remainder of division operation).

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Predefined variables of awk Up User Defined variables in awk


LSST v1.05 > Chapter 7 > User Defined variables in awk


User Defined variables in awk
You can also define your own variable in awk program, as follows:
$ cat > math1
{
no1 = $1
no2 = $2
ans = $1 + $2
print no1 " + " no2 " = " ans
}
Run the program as follows
$ awk -f math1
15
1+5=6
In the above program, no1, no2, ans all are user defined variables. Value of first and second field are
assigned to no1, no2 variable respectively and the addition to ans variable. Value of variable can be
printed using print statement as, print no1 " + " no2 " = " ans. Note that print statement prints whatever
enclosed in double quotes (" text ") as it is. If string is not enclosed in double quotes its treated as
variable. Also above two program takes input from stdin (Keyboard) instead of file.
Now try the following awk program and note down its output.
$ cat > bill
{
total = $3 * $4
recno = $1
item = $2
print recno item " Rs." total
}
Run it as
$ awk -f bill inven
1.Pen Rs.100
2.Pencil Rs.20
3.Rubber Rs.10.5
4.Cock Rs.91
Here we are printing the total price of each product (By multiplying third field with fourth field).
Following program prints total price of each product as well as the Grand total of all product in the
bracket.



$ cat > bill1
{
total = $3 * $4
recno = $1
item = $2
gtotal = gtotal + total
print recno item " Rs." total " [Total Rs." gtotal "] "
}

Run the above awk program as follows:
$ awk -f bill1 inven
1.Pen Rs.100 [Total Rs.100]
2.Pencil Rs.20 [Total Rs.120]
3.Rubber Rs.10.5 [Total Rs.130.5]
4.Cock Rs.91 [Total Rs.221.5]
In this program, gtotal variable holds the grand total. It adds the total of each product as gtotal = gtotal +
total. Finally this total is printed with each record in the bracket. But their is one problem with our script,
Grand total mostly printed at the end of all record. To solve this problem we have to use special BEGIN
and END Patterns of awk. First take the example,
$ cat > bill2
BEGIN {
print "---------------------------"
print "Bill for the 4-March-2001. "
print "By Vivek G Gite. "
print "---------------------------"
}

{
total = $3 * $4
recno = $1
item = $2
gtotal += total
}

END {
print "---------------------------"
print "Total Rs." gtotal
print "==========================="
}
Run it as
$awk -f bill2 inven
---------------------------
Bill for the 4-March-2001.



By Vivek G Gite.
---------------------------
1.Pen Rs.100
2.Pencil Rs.20
3.Rubber Rs.10.5
4.Cock Rs.91
---------------------------
Total Rs.221.5
===============
Now the grand total is printed at the end. In above program BEGIN and END patters are used. BEGIN
instruct awk, that perform BEGIN actions before the first line (Record) has been read from database file.
Use BEGIN pattern to set value of variables, to print heading for report etc. General syntax of BEGIN is
as follows
Syntax:
BEGIN {
action 1
action 2
action N
}
END instruct awk, that perform END actions after reading all lines (RECORD) from the database file.
General syntax of END is as follows:
END {
action 1
action 2
action N
}
In our example, BEGIN is used to print heading and END is used print grand total.

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Doing arithmetic with awk Up Use of printf statement


LSST v1.05 > Chapter 7 > Use of printf statement


Use of printf statement
Next example shows the use of special printf statement
$ cat > bill3
BEGIN {
printf "Bill for the 4-March-2001.n"
printf "By Vivek G Gite.n"
printf "---------------------------n"
}

{
total = $3 * $4
recno = $1
item = $2
gtotal += total
printf "%d %s Rs.%fn", recno, item, total
#printf "%2d %-10s Rs.%7.2fn", recno, item, total
}

END {
printf "---------------------------n"
printf "Total Rs. %fn" ,gtotal
#printf "tTotal Rs. %7.2fn" ,gtotal
printf "===========================n"
}
Run it as follows:
By Vivek G Gite.
---------------------------
1 Pen Rs.100.000000
2 Pencil Rs.20.000000
3 Rubber Rs.10.500000
4 Cock Rs.91.000000
---------------------------
Total Rs. 221.500000
===============
In above example printf statement is used to print formatted output of the variables or text. General
syntax of printf as follows:



Syntax:
printf "format" ,var1, var2, var N
If you just want to print any text using printf as follows
printf "Hello"
printf "Hello Worldn"
In last example n is used to print new line. Its Part of escape sequence following may be also used:
t for tab
a Alert or bell
" Print double quote etc
For e.g. printf "nAn apple a day, keeps awaytttDoctornaa"
It will print text on new line as :
An apple a day, keeps away Doctor
Notice that twice the sound of bell is produced by aa. To print the value of decimal number use %d as
format specification code followed by the variable name. For e.g. printf "%d" , no1
It will print the value of no1. Following table shows such common format specification code:
Format Specification Code Meaning Example
{
isminor = "y"
%c Character
printf "%c" , isminor
}
{
n = 10
%d Decimal number such as 10,-5 etc
printf "%d",n
}
{
Hexadecimal number such as 0xA, n = 10
%x
0xffff etc printf "%x",n
}
{
str1 = "Welcome to Linux!"
%s String such as "vivek", "Good buy" printf "%s", str1
printf "%s", "Can print ?"
}

To run above example simply create any awk program file as follows
$ cat > p_demo
BEGIN {
n = 10
printf "%d", n
printf "nAn apple a day, keeps awaytttDoctornaa"
}



Run it as
$ awk -f p_demo
10
An apple a day, keeps away Doctor
Write awk program to test format specification code. According to your choice.

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User Defined variables in awk Up Use of Format Specification Code


LSST v1.05 > Chapter 7 > Use of Format Specification Code


Use of Format Specification Code
$ cat > bill4
BEGIN {
printf "---------------------------n"
}

{
total = $3 * $4
recno = $1
item = $2
gtotal += total
printf "%2d %-10s Rs.%7.2fn", recno, item, total
}

END {
printf "---------------------------n"
printf "tTotal Rs. %6.2fn" ,gtotal
printf "===========================n"
}
Run it as
By Vivek G Gite.
---------------------------
1 Pen Rs. 100.00
2 Pencil Rs. 20.00
3 Rubber Rs. 10.50
4 Cock Rs. 91.00
---------------------------
Total Rs. 221.50
===============
From the above output you can clearly see that printf can format the output. Let's try to understand
formatting of printf statement. For e.g. %2d, number between % and d, tells the printf that assign 2
spaces for value. Same way if you write following awk program ,


LSST v1.05 > Chapter 7 > Use of Format Specification Code

$ cat > prf_demo
{
na = $1
printf "|%s|", na
printf "|%10s|", na
printf "|%-10s|", na
}
Run it as follows (and type the God)
$ awk -f prf_demo
God
|God|
| God|
|God |
(press CTRL + D to terminate)
printf "|%s|", na Print God as its
printf "|%10s|",
Print God Word as Right justified.
na
printf "|%-10s|", Print God Word as left justified. (- means left
na justified)

Same technique is used in our bill4 awk program to print formatted output. Also the statement like gtotal
+= total, which is equvalent to gtotal = gtotal + total. Here += is called assignment operator. You can use
following assignment operator:
Assignment
Use for Example Equivalent to
operator
a += 10 a = a + 10
+= Assign the result of addition
d += c a=a+c
Assign the result of a -= 10 a = a - 10
-=
subtraction d -= c a=a-c
Assign the result of a *= 10 a = a * 10
*=
multiplication d *= c a=a*c
a %= 10 a = a % 10
%= Assign the result of modulo
d %= c a=a%c

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Use of printf statement Up if condition in awk


LSST v1.05 > Chapter 7 > if condition in awk


if condition in awk
General syntax of if condition is as follows:
Syntx:
if ( condition )
{
Statement 1
Statement 2
Statement N
if condition is TRUE
}
else
{
Statement 1
Statement 2
Statement N
if condition is FALSE
}
Above if syntax is selfexplontary, now lets move to next awk program

$ awk > math2
BEGIN {
myprompt = "(To Stop press CTRL+D) > "
printf "Welcome to MyAddtion calculation awk program v0.1n"
printf "%s" ,myprompt
}

{
no1 = $1
op = $2
no2 = $3
ans = 0

if ( op == "+" )
{
ans = $1 + $3
printf "%d %c %d = %dn" ,no1,op,no2,ans
}



else
{
printf "Opps!Error I only know how to add.nSyntax: number1 +
number2n"
}
}

END {
printf "nGoodbuy %sn" , ENVIRON["USER"]
}
Run it as follows (Give input as 5 + 2 and 3 - 1 which is shown in bold words)
$awk -f math2
Welcome to MyAddtion calculation awk program v0.1
(To Stop press CTRL+D) > 5 + 2
5+2=7
(To Stop press CTRL+D) > 3 - 1
Opps!Error I only know how to add.
Syntax: number1 + number2
(To Stop press CTRL+D) >
Goodbuy vivek
In the above program various, new concept are introduce so lets try to understand them step by step
Start of BEGIN
BEGIN {
Pattern
Define user
defined variable
Print welcome
message and
value of
myprompt
variable.
End of BEGIN
}
Pattern
Now start to
{
process input
Assign first,
no1 = $1 second, third,
op = $2 variables value
no2 = $3 to no1, op, no2
ans = 0 variables
respectively



If command is
if ( op == "+" )
used for decision
{
making in awk
ans = no1 + no2
program. Here if
value of variable
op is "+" then
}
addition is done
else
and result is
{
printed on
printf "Opps!Error I only know how to add.nSyntax:number1+ number2n"
screen, else error
message is
}
shown on screen.
Stop all inputted
} lines are
process.
END patterns
END { start here.
printf "nGoodbuy %sn" , ENVIRON["USER"] Which says
} currently log on
user Goodbuy.

ENVIRON is the one of the predefined system variable that is array. Array is made up of different
element. ENVIRON array is also made of elements. It allows you to access system variable (or variable
in your environment). Give set command at shell prompt to see list of your environment variable. You
can use variable name to reference any element in this array. For e.g. If you want to print your home
directory you can write printf as follows:
printf "%s is my sweet home", ENVIRON["HOME"]

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Use of Format Specification Code Up Loops in awk


LSST v1.05 > Chapter 7 > Loops in awk


Loops in awk
For loop and while loop are used for looping purpose in awk.
Syntax of for loop
Syntax:
for (expr1; condition; expr2)
{
Statement 1
Statement 2
Statement N
}
Statement(s) are executed repeatedly UNTIL the condition is true. BEFORE the first iteration, expr1 is
evaluated. This is usually used to initialize variables for the loop. AFTER each iteration of the loop,
expr2 is evaluated. This is usually used to increment a loop counter.
Example:
$ cat > while01.awk
BEGIN{
printf "Press ENTER to continue with for loop example from LSST
v1.05r3n"
}
{
sum = 0
i = 1
for (i=1; i<=10; i++)
{
sum += i; # sum = sum + i
}
printf "Sum for 1 to 10 numbers = %d nGoodbuy!nn", sum
exit 1
}
Run it as follows:
$ awk -f while01.awk
Press ENTER to continue with for loop example from LSST v1.05r3
Sum for 1 to 10 numbers = 55
Goodbuy
Above for loops prints the sum of all numbers between 1 to 10, it does use very simple for loop to
achieve this. It take number from 1 to 10 using i variable and add it to sum variable as sum = previous
sum + current number (i.e. i).



Consider one more example of for loop:
$ cat > for_loop
BEGIN {
printf "To test for loopn"
printf "Press CTRL + C to stopn"
}
{
for(i=0;i<NF;i++)
{
printf "Welcome %s, %d times.n" ,ENVIRON["USER"], i
}
}
Run it as (and give input as Welcome to Linux!)
$ awk -f for_loop
To test for loop
Press CTRL + C to Stop
Welcome to Linux!
Welcome vivek, 0 times.
Program uses for loop as follows:
Set the value of i to 0 (Zero); Continue as long as
value of i is less than NF (Remember NF is built in
for(i=0;i<NF;i++)
variable, which mean Number of Fields in record);
increment i by 1 (i++)
printf "Welcome %s, %d times.n" Print "Welcome...." message, with user name who
,ENVIRON["USER"], i is currently log on and value of i.

Here i++, is equivalent to i = i + 1 statement. ++ is increment operator which increase the value of
variable by one and -- is decrement operator which decrease the value of variable by one. Don't try i+++,
to increase the value of i by 2 (since +++ is not valid operator), instead try i+= 2.
You can use while loop as follows:
Syntax:
while (condition)
{
statement1
statement2
statementN
Continue as long as given condition is TRUE
}
While loop will continue as long as given condition is TRUE. To understand the while loop lets write



one more awk script:
$ cat > while_loop
{
no = $1
remn = 0
while ( no > 1 )
{
remn = no % 10
no /= 10
printf "%d" ,remn
}
printf "nNext number please (CTRL+D to stop):";
}
Run it as
$awk -f while_loop
654
456
Next number please(CTRL+D to stop):587
785
Next number please(CTRL+D to stop):
Here user enters the number 654 which is printed in reverse order i.e. 456. Above program can be
explained as follows:
no = $1 Set the first fields ($1) value to no.
remn = 0 Set remn variable to zero
{ Start the while loop
Continue the loop as long as value of no is greater than
while (no > 1)
one
Find the remainder of no variable, and assign result to
remn = no % 10
remn variable.
no /= 10 Divide the no by 10 and store result to no variable.
print "%d", remn Print the remn (remainder) variables value.
End of while loop, since condition (no>1) is not true i.e
}
false condition..
printf "nNext number please (CTRL+D to
Prompt for next number
stop):";

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if condition in awk Up Real life example in awk


LSST v1.05 > Chapter 7 > Real life example in awk


Real life example in awk
Before learning more features of awk its time to see some real life example in awk.
Our first Example
I would like to read name of all files from the file and copy them to given destination directory. For e.g.
The file filelist.conf; looks something as follows:
/home/vivek/awks/temp/file1 /home/vivek/final
In above file first field ($1) is the name of file that I would like to copy to the given destination directory
($2 - second field) i.e. copy /home/vivek/awks/temp/file1 file to /home/vivek/final directory. For this
purpose write the awk program as follows:

$ cat > temp2final.awk
#
#temp2final.awk
#Linux Shell Scripting Tutorial v1.05, March 2001
#Author: Vivek G Gite
#

BEGIN{
}

#
# main logic is here
#
{
sfile = $1
dfile = $2
cpcmd = "cp " $1 " " $2
printf "Coping %s to %sn",sfile,dfile
system(cpcmd)
}

#
# End action, if any, e.g. clean ups
#
END{



}
Run it as follows:
$ awk -f temp2final.awk filelist.conf
Above awk Program can be explained as follows:
sfile = $1 Set source file path i.e. first field ($1) from the file filelist.conf
dfile = $2 Set source file path i.e. second field ($2) from the file filelist.conf
Use your normal cp command for copy file from source to destination.
cpcmd = "cp " $1 " " $2
Here cpcmd, variable is used to construct cp command.
printf "Coping %s to
Now print the message
%sn",sfile,dfile
system(cpcmd) Issue the actual cp command using system(), function.

system() function execute given system command. For e.g. if you want to remove file using rm command
of Linux, you can write system as follows
system("rm foo")
OR
dcmd = "rm " $1
system(dcmd)
The output of command is not available to program; but system() returns the exit code (error code) using
which you can determine whether command is successful or not. For e.g. We want to see whether rm
command is successful or not, you can write code as follows:
$ cat > tryrmsys
{
dcmd = "rm " $1
if ( system(dcmd) != 0 )
printf "rm command not successfuln"
else
printf "rm command is successful and %s file is removed n",
$1
}
Run it as (assume that file foo exist and bar does not exist)
$ awk -f tryrmsys
foo
rm command is successful and foo file is removed
bar
rm command not successful
(Press CTRL + D to terminate)
Our Second Example:
As I write visual installation guide, I use to capture lot of images for my work, while capturing images I



saved all images (i.e. file names) in UPPER CASE for e.g.
RH7x01.JPG,RH7x02.JPG,...RH7x138.JPG.
Now I would like to rename all files to lowercase then I tried with following two scripts:
up2low and rename.awk

up2low can be explained as follows:
Statements/Command Explanation
AWK_SCRIPT="rename.awk" Name of awk scripts that renames file
awkspath=$HOME/bin/$AWK_SCRIPT Where our awk script is installed usually it
should be installed under
your-home-directory/bin (something like
/home/vivek/bin)
ls -1 > /tmp/file1.$$ List all files in current working directory line
by line and send output to /tmp/file1.$$ file.
tr "[A-Z]" "[a-z]" < /tmp/file1.$$ > /tmp/file2.$$ Now convert all Uppercase filename to
lowercase and store them to /tmp/file2.$$
file.
paste /tmp/file1.$$ /tmp/file2.$$ > /tmp/tmpdb.$$ Now paste both Uppercase filename and
lowercase filename to third file called
/tmp/tmpdb.$$ file
rm -f /tmp/file1.$$ Remove both file1.$$ and file2.$$ files
rm -f /tmp/file2.$$
if [ -f $awkspath ]; then See if rename.awk script installed, if not
awk -f $awkspath /tmp/tmpdb.$$ installed give error message on screen. If
else installed call the rename.awk script and give
echo -e "n$0: Fatal error - $awkspath not found" it /tep/tepdb.$$ path to read all filenames
echo -e "nMake sure $awkspath is set correctly in $0 from this file.
scriptn"
fi
rm -f /tmp/tmpdb.$$ Remove the temporary file.

rename.awk can be explained as follows:
Statements/Command Explanation



isdir1 = "[ -d " $1 " ] " This expression is quite tricky. Its
something as follows:
isdir1 = [ -d $1 ]
Which means see if directory exists
using [ expr ]. As you know [ expr ] is
used to test whether expr is true or not.
So we are testing whether directory exist
or not.
What does $1 mean? If you remember,
in awk $1 is the first field.
isdir2 = "[ -d " $2 " ] " As above except it test for second field
as
isdir2 = [ -d $2 ]
i.e. Whether second field is directory or
not.
scriptname = "up2low" Our shell script name (up2low) and awk
awkscriptname = "rename.awk" script name (rename.awk).
sfile = $1 Source file
dfile = $2 Destination file
if ( sfile == scriptname || sfile == awkscriptname ) Make sure we don't accidentally rename
next our own scripts, if scripts are in current
working directory
else if( ( system(isdir1) ) == 0 || system((isdir2)) == 0 ) Make sure source or destination are files
{ and not the directory. We check this
printf "%s or %s is directory can't rename it to lower using [ expr ] command of bash. From
casen",sfile,dfile the awk script you can called or invoke
next # continue with next recored (as official we called it) the [ expr ] if
} directory do exists it will return true
(indicated by zero) and if not it will
return nonzero value.
else if ( sfile == dfile ) If both source and destination file are
{ same, it mean file already in lower case
printf "Skiping, "%s" is alrady in lowercasen",sfile no need to rename it to lower case.
next
}



else # everythink is okay rename it to lowercase Now if source and destination files are
{ not
mvcmd = "mv " $1 " " $2 q Directories
printf "Renaming %s to %sn",sfile,dfile
q Name of our scripts
system(mvcmd)
} q And File is in UPPER CASE

Then rename it to lowercase by issuing
command mv command.

Note that if you don't have files name in UPPER case for testing purpose you can create files name as
follows:
$ for j in 1 2 3 4 5 6 7 8 9 10; do touch TEMP$j.TXT; done
Above sample command creates files as TEMP1.TXT,TEMP2.TXT,....TEMP10.TXT files.
Run it as follows:
$ up2low
Letters or letters is directory can't rename it to lower case
RH6_FILES or rh6_files is directory can't rename it to lower case
Renaming RH7x01.JPG to rh7x01.jpg
....
..
....
On my workstation above output is shown.

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Loops in awk Up awk miscellaneous


LSST v1.05 > Chapter 7 > awk miscellaneous


awk miscellaneous
You can even take input from keyboard while running awk script, try the following awk script:
$ cat > testusrip
BEGIN {
printf "Your name please:"
getline na < "-"
printf "%s your age please:",na
getline age < "-"
print "Hello " na, ", next year you will be " age + 1
}
Save it and run as
$ awk -f testusrip
Your name please: Vivek
Vivek your age please: 26
Hello Vivek, next year you will be 27
Here getline function is used to read input from keyboard and then assign the data (inputted from
keyboard) to variable.
Syntax:
getline variable-name < "-"
| | |
1 2 3
1 --> getline is function name
2 --> variable-name is used to assign the value read from input
3 --> Means read from stdin (keyboard)
To reading Input from file use following
Syntax:
getline < "file-name"
Example:
getline < "friends.db"
To reading Input from pipe use following
Syntax:
"command" | getline
Example:


LSST v1.05 > Chapter 7 > awk miscellaneous

$ cat > awkread_file
BEGIN {
"date" | getline
print $0
}

Run it as
$ awk -f awkread_file
Fri Apr 12 00:05:45 IST 2002
Command date is executed and its piped to getline which assign the date command output to variable $0.
If you want your own variable then replace the above program as follows
$ cat > awkread_file1
BEGIN {
"date" | getline today
print today
}

Run it as follows:
$ awk -f awkread_file1
Try to understand the following awk script and note down its output.
temp2final1.awk

Prev Home Next
Real life examples in awk Up sed - Quick Introduction


LSST v1.05 > Chapter 7 > sed - Quick Introduction


sed - Quick Introduction
SED is a stream editor. A stream editor is used to perform basic text transformations on an input stream
(a file or input from a pipeline). SED works by making only one pass over the input(s), and is
consequently more efficient. But it is SED's ability to filter text in a pipeline which particularly
distinguishes it from other types of editors.
Before getting started with tutorial you must know basic expression which is covered in our Learning
expressions with ex tutorial. For this part of tutorial create demofile1. After creating the file type
following sed command at shell prompt:
$ sed 's/Linux/UNIX(system v)/' demofile1
Hello World.
I love linux.
.....
...
.....
linux is linux
Above sed command can be explained as follows:
Commands Meaning
sed Start the sed command
's/Linux/UNIX(system Use substitute command to replace Linux with UNIX(system v).
v)/' General syntax of substitute is s/pattern/pattern-to-substitute/'
demofile1 Read the data from demofile1

General Syntax of sed
Syntax:
sed -option 'general expression' [data-file]
sed -option sed-script-file [data-file]
Option can be:

Option Meaning Example
Read the different sed
$ sed -e 'sed-commands' data-file-name
-e command from command
$ sed -e 's/Linux/UNIX(system v)/' demofile1
line.
Read the sed command $sed -f sed-script-file data-file-name
-f
from sed script file. $ sed -f chgdb.sed friends.tdb


LSST v1.05 > Chapter 7 > sed - Quick Introduction

Suppress the output of sed
command. When -n is used
-n $ sed -n '/^*..$/p' demofile2
you must use p command
of print flag.

Prev Home Next
awk miscellaneous Up Redirecting the output of sed command


LSST v1.05 > Chapter 7 > Redirecting the output of sed command


Redirecting the output of sed command
You can redirect the output of sed command to file as follows
$ sed 's/Linux/UNIX(system v)/' demofile1 > file.out
And can see the output using cat command as follows
$ cat file.out

Deleting blank lines
Using sed you can delete all blank line from file as follow
$ sed '/^$/d' demofile1
As you know pattern /^$/, match blank line and d, command deletes the blank line.
Following sed command takes input from who command and sed is used to check whether particular user
is logged or not.
$ who | sed -n '/vivek/p'
Here -n option to sed command, suppress the output of sed command; and /vivek/ is the pattern that we
are looking for, finally if the pattern found its printed using p command of sed.

Prev Home Next
sed - Quick Introduction Up How to write sed scripts?


LSST v1.05 > Chapter 7 > How to write sed scripts?


How to write sed scripts?
Sed command can be grouped together in one text file, this is know as sed script. For next example of
sed script create inven1 data file and create "chg1.sed", script file as follows

Tip: Give .sed extension to sed script, .sh to Shell script and .awk to awk script file(s), this will help you
to identify files quickly.
$ cat > chg1.sed
1i
Price of all items changes from 1st-April-2001
/Pen/s/20.00/19.5/
/Pencil/s/2.00/2.60/
/Rubber/s/3.50/4.25/
/Cock/s/45.50/51.00/
Run the above sed script as follows:
$ sed -f chg1.sed inven1
1. Pen 5 19.5
2. Pencil 10 2.60
3. Rubber 3 4.25
4. Cock 2 51.00
In above sed script, the 1i is the (i) insert command. General Syntax is as follows:
Syntax:
[line-address]i
text
So,
1i
means insert the text "Price of all items changes from 1st-April-2001" at line number 1.
Same way you can use append (a) or change (c) command in your sed script,
General Syntax of append
Syntax:
[line-address]a
text
Example:
/INDIA/ a
E-mail: vg@indiamail.co.in


LSST v1.05 > Chapter 7 > How to write sed scripts?

Find the word INDIA and append (a) "E-mail: vg@indiamail.co.in" text.
General Syntax of change as follows:
Syntax:
[line-address]c
text

Example:
/INDIA/ c
E-mail: vg@indiamail.co.in
Find the word INDIA and change e-mail id to "vg@indiamail.co.in"
Rest of the statements (like /Pen/s/20.00/19.5/) are general substitute statements.

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Redirecting the output of sed command Up More examples of sed


LSST v1.05 > Chapter 7 > More examples of sed


More examples of sed
First create text file demofile2 which is used to demonstrate next sed script examples.
Type following sed command at shell promote:
$ sed -n '/10{2}1/p' demofile2
1001
Above command will print 1001, here in search pattern we have used {2}.
Syntax:
{n,}
At least nth occurrences will be matched. So /10{2} will look for 1 followed by 0 (zero) and {2}, tells sed
look for 0 (zero) for twice.

Matcheing any number of occurrence
Syntax:
{n,m}
Matches any number of occurrence between n and m.
Example:
$ sed -n '/10{2,4}1/p' demofile2
1001
10001
100001
Will match "1001", "10001", "100001" but not "101" or "10000000". Suppose you want to print all line that
begins with *** (three stars or asterisks), then you can type command
$ sed -n '/^*..$/p' demofile2
***
***
Above sed expression can be explianed as follows:
Command Explnation
^ Beginning of line
* Find the asterisk or star ( remove the special meaning of '*' metacharacter)
.. Followed by any two character (you can also use ** i.e. $ sed -n '/^***$/p' demofile2 )
$ End of line (So that only three star or asterisk will be matched)
/p Print the pattern.

Even you can use following expression for the same purpose
$ sed -n '/^*{2,3}$/p' demofile2
Now following command will find out lines between *** and *** and then delete all those line
$sed -e '/^*{2,3}$/,/^*{2,3}$/d' demofile2 > /tmp/fi.$$
$cat /tmp/fi.$$



Above expression can be explained as follows
Expression Meaning
^ Beginning of line
Find the asterisk or star ( remove the special meaning of '*'
*
metacharacter)
{2,3} Find next two asterisk
$ End of line
, Next range or search pattern
^*{2,3}$ Same as above
d Now delete all lines between *** and *** range

You can group the commands in sed - scripts as shown following example
$ cat > dem_gsed
/^*{2,3}$/,/^*{2,3}$/{
/^$/d
s/Linux/Linux-Unix/
}<
Now save above sed script and run it as follows:
$ sed -f dem_gsed demofile2 > /tmp/fi.$$
$ cat /tmp/fi.$$
Above sed scripts finds all line between *** and *** and performance following operations
1) Delete blank line, if any using /^$/d expression.
2) Substitute "Linux-Unix" for "Linux" word using s/Linux/Linux-Unix/ expression.
Our next example removes all blank line and converts multiple spaces into single space, for this purpose you
need demofile3 file. Write sed script as follows:
$ cat > rmblksp
/^$/d
s/ */ /g<
Run above script as follows:
$ sed -f rmblksp demofile3
Welcome to world of sed what sed is?
I don't know what sed is but I think
Rani knows what sed Is
--------------------------------------------------
Above script can be explained as follows:
Expression Meaning
/^$/d Find all blank line and delete is using d command.
Find two or more than two blank space and replace it with single
s/ */ /g
blank space



Note that indicates two blank space and indicate one blank space.
For our next and last example create database file friends
Our task is as follows for friends database file:
1)Find all occurrence of "A'bad" word replace it with "Aurangabad" word
2)Exapand MH state value to Maharastra
3)Find all blank line and replace with actual line (i.e. ========)
4)Instert e-mail address of each persons at the end of persons postal address. For each person e-mail ID is
different
To achieve all above task write sed script as follows:
$ cat > mkchgfrddb
s/A.bad/Aurangabad/g
s/MH/Maharastra/g
s/^$/===================================================================/g
/V.K. /{
N
N
a
email:vk@fackmail.co.in
}

/M.M. /{
N
N
a
email:mm@fackmail.co.in
}

/R.K. /{
N
N
a
email:rk@fackmail.co.in
}

/A.G. / {
N
N
a
email:ag@fackmail.co.in
}

/N.K. / {
N
N
a
email:nk@fackmail.co.in



}
Run it as follows:
$ sed -f mkchgfrddb friends > updated_friendsdb
$ cat updated_friendsdb

Above script can be explained as follows:
Expression Meaning
Substitute Aurangabad for A'bad. Note that here second character
in A'bad is ' (single quote), to match this single quote we have to
s/A.bad/Aurangabad/g
use . (DOT - Special Metacharcter) that matches any single
character.
s/MH/Maharastra/g Substitute Maharastra for MH
s/^$/==========/g Substitute blank line with actual line
/V.K. /{
Match the pattern and follow the command between { and }, if
N
pattern found. Here we are finding each friends initial name if it
N
matches then we are going to end of his address (by giving N
a
command twice) and appending (a command) friends e-mail
email:vk@fackmail.co.in
address at the end.
}

Our last examples shows how we can manipulate text data files using sed. Here our tutorial on sed/awk ends
but next version (LSST ver 2.0) will cover more real life examples, case studies using all these tools, plus
integration with shell scripts etc.

Prev Home Next
How to write sed scripts? Up Examples of Shell Scripts


LSST v1.05 > Chapter 8 > Examples of Shell Scripts
Prev Chapter 8: Examples of Shell Scripts Next

More examples of Shell Script (Exercise for You :-)
These exercises are to test your general understanding of the shell scripting. My advise is first try to write this shell script yourself so
that you understand how to put the concepts to work in real life scripts. For sample answer to exercise you can refer the shell script
file supplied with this tutorial. If you want to become the good programmer then your first habit must be to see the good code/samples
of programming language then practice lot and finally implement your own code (and become the good programmer!!!).
Q.1. How to write shell script that will add two nos, which are supplied as command line argument, and if this two nos are not given
show error and its usage
Answer: See Q1 shell Script.

Q.2.Write Script to find out biggest number from given three nos. Nos are supplied as command line argument. Print error if sufficient
arguments are not supplied.

Q.3.Write script to print nos as 5,4,3,2,1 using while loop.
Q.4. Write Script, using case statement to perform basic math operation as
follows
+ addition
- subtraction
x multiplication
/ division
The name of script must be 'q4' which works as follows
$ ./q4 20 / 3, Also check for sufficient command line arguments
Q.5.Write Script to see current date, time, username, and current directory
Q.6.Write script to print given number in reverse order, for eg. If no is 123 it must print as 321.
Q.7.Write script to print given numbers sum of all digit, For eg. If no is 123 it's sum of all digit will be 1+2+3 = 6.
Q.8.How to perform real number (number with decimal point) calculation in Linux
Answer: Use Linux's bc command
Q.9.How to calculate 5.12 + 2.5 real number calculation at $ prompt in Shell ?
Answer: Use command as , $ echo 5.12 + 2.5 | bc , here we are giving echo commands output to bc to calculate the 5.12 + 2.5
Q.10.How to perform real number calculation in shell script and store result to
third variable , lets say a=5.66, b=8.67, c=a+b?
Q.11.Write script to determine whether given file exist or not, file name is supplied as command line argument, also check for
sufficient number of command line argument

Q.12.Write script to determine whether given command line argument ($1) contains "*" symbol or not, if $1 does not contains "*"
symbol add it to $1, otherwise show message "Symbol is not required". For e.g. If we called this script Q12 then after giving ,
$ Q12 /bin
Here $1 is /bin, it should check whether "*" symbol is present or not if not it should print Required i.e. /bin/*, and if symbol present
then Symbol is not required must be printed. Test your script as
$ Q12 /bin


$ Q12 /bin/*
Answer: See Q12 shell Script

Q.13. Write script to print contains of file from given line number to next given number of lines. For e.g. If we called this script as
Q13 and run as
$ Q13 5 5 myf , Here print contains of 'myf' file from line number 5 to next 5 line of that file.

Q.14. Write script to implement getopts statement, your script should understand following command line argument called this script
Q14,
Q14 -c -d -m -e
Where options work as
-c clear the screen
-d show list of files in current working directory
-m start mc (midnight commander shell) , if installed
-e { editor } start this { editor } if installed

Q.15. Write script called sayHello, put this script into your startup file called .bash_profile, the script should run as soon as you logon
to system, and it print any one of the following message in infobox using dialog utility, if installed in your system, If dialog utility is
not installed then use echo statement to print message : -
Good Morning
Good Afternoon
Good Evening , according to system time.
Q.16. How to write script, that will print, Message "Hello World" , in Bold and Blink effect, and in different colors like red, brown etc
using echo command.
Q.17. Write script to implement background process that will continually print current time in upper right corner of the screen , while
user can do his/her normal job at $ prompt.
Q.18. Write shell script to implement menus using dialog utility. Menu-items and action according to select menu-item is as follows:
Menu-Item Purpose Action for Menu-Item
Date/time To see current date time Date and time must be shown using infobox of dialog utility
Calendar To see current calendar Calendar must be shown using infobox of dialog utility
First ask user name of directory where all files are present, if no name
of directory given assumes current directory, then show all files only of
that directory, Files must be shown on screen using menus of dialog
Delete To delete selected file
utility, let the user select the file, then ask the confirmation to user
whether he/she wants to delete selected file, if answer is yes then delete
the file , report errors if any while deleting file to user.
Exit To Exit this shell script Exit/Stops the menu driven program i.e. this script

Note: Create function for all action for e.g. To show date/time on screen create function show_datetime().

Q.19. Write shell script to show various system configuration like
1) Currently logged user and his logname
2) Your current shell
3) Your home directory
4) Your operating system type
5) Your current path setting
6) Your current working directory
7) Show Currently logged number of users
8) About your os and version ,release number , kernel version
9) Show all available shells


10) Show mouse settings
11) Show computer cpu information like processor type, speed etc
12) Show memory information
13) Show hard disk information like size of hard-disk, cache memory, model etc
14) File system (Mounted)

Q.20.Write shell script using for loop to print the following patterns on screen
for2 for3 for4

for5 for6 for7

for8 for8 for9

Answer: Click on above the links to see the scripts.
Q.21.Write shell script to convert file names from UPPERCASE to lowercase file names or vice versa.
Answer: See the rename.awk - awk script and up2sh shell script.

Prev Home Next
More examples of sed Up Other Resources


LSST v1.05 > Chapter 9 > Introduction

Prev Chapter 9: Other Resources Next

Introduction
This is new chapter added to LSST v1.05r3, its gives more references to other material available on shell
scripting on Net or else ware. It also indicates some other resources which might be useful while
Appendix - A Information
This tutorial/document is useful for beginners who wish
Appendix - A to learn Linux file system, it covers basic concept of file
system, commands or utilities related with file system. It
Linux File Server Tutorial (LFST) version
will explain basic file concepts such as what is file &
b0.1 Rev. 2
directories, what are the mount points, how to use cdrom
or floppy drive under Linux.
This command reference is specially written for the
Appendix - B LSST. It contains command name, general syntax
followed by an example. This is useful while
Linux Command Reference (LCR)
programming shell and you can use as Quick Linux
Command Reference guide.

More information on upcoming edition of this tutorial.

Prev Home Next
Examples of Shell Scripts Up About the author


LSST v1.05 > About Author

Prev Chapter 9: Other Resources Next

About Author
Vivek G. Gite runs small firm called "Cyberciti Computers" and *nix Solution firm nixCraft. He is
freelance software developer and also teaches computer hardware, networking and Linux/Unix to
beginners. He is also working with various Computers Firms as Technology Consultant. Currently he
writes article on Linux/Unix, LSST is one of such article/document. His future plan includes more
article/documents on Linux especially for beginners. If you have any suggestion or new ideas or problem
with this tutorial, please feel free to contact author using following e-mail ID.
How do I contact the author?
I can be contacted by e-mail: vivek@nixcraft.com.

Where do I find the latest version?
Please visit http://www.cyberciti.biz/nixcraft/linux/docs/ for latest version of this Tutorial/Document as
well as for other tutorial/documents.
Other Information
This tutorial is prepared with help of all valuable material from web as well as from on-line help of
Linux (man and info pages), Linux how-to's etc. Also special thanks to Ashish for his valuable
suggestion for this tutorial/document.

All the trademarks are acknowledged and used for identification purpose only.

Prev Home Next
Other Resources Up About this Document

http://www.cyberciti.biz/pdf/lsst/aboutauth.html [7/29/2002 6:54:01 PM]

LSST v1.05 > About this Document

Prev Chapter 9 : Other Resources

About this Document
This document is Copyright (C) 1999, 2000, 2001,2002 by Vivek G. Gite <vivek@nixcraft.com>. It may
be freely distributed in any medium as long as the text (including this notice) is kept intact and the
content is not modified, edited, added to or otherwise changed. Formatting and presenting may be
modified. Small excerpts may be made as long as the full document is properly and conspicuously
referenced.
If you do the mirror of this document, please send e-mail to the address above, so that you can be
informed of updates.
All trademark within are property of their respective holders.
Although the author believes the contents to be accurate at the time of publication, no liability is assumed
for them, their application or any consequences thereof. if any misrepresentations, errors or other need of
clarification is found, please contact the author immediately.
The latest copy of this document can always be obtained from:
http://www.cyberciti.biz/nixcraft/linux/docs/

Last updated Linux Shell Scripting Tutorial v1.05r3 (LSST) - on Thu., July, 04, 2002.

Prev Home An UniqLinux Features
About the author Up

http://www.cyberciti.biz/pdf/lsst/aboutthisdoc.html [7/29/2002 6:54:03 PM]

http://www.cyberciti.biz/pdf/lsst/scripts/q1

#!/bin/bash
#
# Linux Shell Scripting Tutorial 1.05r3, Summer-2002
#
# Written by Vivek G. Gite <vivek@nixcraft.com>
#
# Latest version can be found at http://www.nixcraft.com/
#
# Q1.Script to sum to nos
#

if [ $# -ne 2 ]
then
echo "Usage - $0 x y"
echo " Where x and y are two nos for which I will print sum"
exit 1
fi
echo "Sum of $1 and $2 is `expr $1 + $2`"
#
# ./ch.sh: vivek-tech.com to nixcraft.com referance converted using this tool
# See the tool at http://www.nixcraft.com/uniqlinuxfeatures/tools/
#

http://www.cyberciti.biz/pdf/lsst/scripts/q1 [7/29/2002 6:54:23 PM]


#!/bin/bash
#
#
#
#
# Q2. Script to find out bigest number
#
# Algo:
# 1) START: Take three nos as n1,n2,n3.
# 2) Is n1 is greater than n2 and n3, if yes
# print n1 is biggest no goto step 5, otherwise goto next step
# 5) END
#
#

if [ $# -ne 3 ]
then
echo "$0: number1 number2 number3 are not given" >&2
exit 1
fi
n1=$1
n2=$2
n3=$3
if [ $n1 -gt $n2 ] && [ $n1 -gt $n3 ]
then
echo "$n1 is Biggest number"
elif [ $n2 -gt $n1 ] && [ $n2 -gt $n3 ]
then
elif [ $n3 -gt $n1 ] && [ $n3 -gt $n2 ]
then
elif [ $1 -eq $2 ] && [ $1 -eq $3 ] && [ $2 -eq $3 ]
then
echo "All the three numbers are equal"
else
echo "I can not figure out which number is bigger"
fi

#
#



#!/bin/bash
#
#
#
#
# Q3
# Algo:
# 1) START: set value of i to 5 (since we want to start from 5, if you
# want to start from other value put that value)
# 2) Start While Loop
# 3) Chechk, Is value of i is zero, If yes goto step 5 else
# continue with next step
# 4) print i, decement i by 1 (i.e. i=i-1 to goto zero) and
# goto step 3
# 5) END
#
i=5
while test $i != 0
do
echo "$i
"
i=`expr $i - 1`
done
#
#



#!/bin/bash
#
#
#
#
# Q4
#

if test $# = 3
then
case $2 in
+) let z=$1+$3;;
-) let z=$1-$3;;
/) let z=$1/$3;;
x|X) let z=$1*$3;;
*) echo Warning - $2 invalied operator, only +,-,x,/ operator allowed
exit;;
esac
echo Answer is $z
else
echo "Usage - $0 value1 operator value2"
echo " Where, value1 and value2 are numeric values"
echo " operator can be +,-,/,x (For Multiplication)"
fi

#
#



#!/bin/bash
#
#
#
#
# Q5
#
echo "Hello, $LOGNAME"
echo "Current date is `date`"
echo "User is `who i am`"
echo "Current direcotry `pwd`"

#
#



#!/bin/bash
#
#
#
#
# Script to reverse given no
#
# Algo:
# 1) Input number n
# 2) Set rev=0, sd=0
# 3) Find single digit in sd as n % 10 it will give (left most digit)
# 4) Construct revrse no as rev * 10 + sd
# 5) Decrment n by 1
# 6) Is n is greater than zero, if yes goto step 3, otherwise next step
# 7) Print rev
#
if [ $# -ne 1 ]
then
echo "Usage: $0 number"
echo " I will find reverse of given number"
echo " For eg. $0 123, I will print 321"
exit 1
fi

n=$1
rev=0
sd=0

while [ $n -gt 0 ]
do
sd=èxpr $n % 10`
rev=èxpr $rev * 10 + $sd`
n=èxpr $n / 10`
done
echo "Reverse number is $rev"

#
#



#!/bin/bash
#
#
#
#
# Algo:
# 1) Input number n
# 2) Set sum=0, sd=0
# 3) Find single digit in sd as n % 10 it will give (left most digit)
# 4) Construct sum no as sum=sum+sd
# 5) Decrment n by 1
# 6) Is n is greater than zero, if yes goto step 3, otherwise next step
# 7) Print sum
#
if [ $# -ne 1 ]
then
echo "Usage: $0 number"
echo " I will find sum of all digit for given number"
echo " For eg. $0 123, I will print 6 as sum of all digit (1+2+3)"
exit 1
fi

n=$1
sum=0
sd=0
while [ $n -gt 0 ]
do
sd=èxpr $n % 10`
sum=èxpr $sum + $sd`
n=èxpr $n / 10`
done
echo "Sum of digit for numner is $sum"

#
#



#!/bin/bash
#
#
#
#
# Q10
#
a=5.66
b=8.67
c=`echo $a + $b | bc`
echo "$a + $b = $c"

#
#



#!/bin/bash
#
#
#
#
# Q11

if [ $# -ne 1 ]
then
echo "Usage - $0 file-name"
exit 1
fi

if [ -f $1 ]
then
echo "$1 file exist"
else
echo "Sorry, $1 file does not exist"
fi

#
#



#!/bin/bash
#
#
#
#
# Q12
# Script to check whether "/*" is included, in $1 or not
#

cat "$1" > /tmp/file.$$ 2>/tmp/file0.$$

grep "*" /tmp/file.$$ >/tmp/file0.$$

if [ $? -eq 1 ]
then
echo "Required i.e. $1/*"
else
echo "Symbol is Not required"
fi

rm -f /tmp/file.$$
rm -f /tmp/file0.$$
#
#



#!/bin/bash
#
#
#
#
# Q13
#
# Shell script to print contains of file from given line no to next
# given numberlines
#

#
# Print error / diagnostic for user if no arg's given
#
if [ $# -eq 0 ]
then
echo "$0:Error command arguments missing!"
echo "Usage: $0 start_line uptoline filename"
echo "Where start_line is line number from which you would like to print file"
echo "uptoline is line number upto which would like to print"
echo "For eg. $0 5 5 myfile"
echo "Here from myfile total 5 lines printed starting from line no. 5 to"
echo "line no 10."
exit 1
fi

#
# Look for sufficent arg's
#

if [ $# -eq 3 ]; then
if [ -e $3 ]; then
tail +$1 $3 | head -n$2
else
echo "$0: Error opening file $3"
exit 2
fi
else
echo "Missing arguments!"
fi

#
#



#!/bin/bash
#
#
#
#
# Q14
# -c clear
# -d dir
# -m mc
# -e vi { editor }
#

#
# Function to clear the screen
#
cls()
{
clear
echo "Clear screen, press a key . . ."
read
return
}

#
# Function to show files in current directory
#
show_ls()
{
ls
echo "list files, press a key . . ."
read
return
}

#
# Function to start mc
#
start_mc()
{
if which mc > /dev/null ; then
mc
echo "Midnight commander, Press a key . . ."
read
else
echo "Error: Midnight commander not installed, Press a key . . ."
read
fi
return
}

#
# Function to start editor
#
start_ed()
{
ced=$1
if which $ced > /dev/null ; then
$ced

http://www.cyberciti.biz/pdf/lsst/scripts/q14 (1 of 2) [7/29/2002 6:55:36 PM]


echo "$ced, Press a key . . ."
read
else
echo "Error: $ced is not installed or no such editor exist, Press a key . . ."
read
fi
return
}

#
# Function to print help
#
print_help_uu()
{
echo "Usage: $0 -c -d -m -v {editor name}";
echo "Where -c clear the screen";
echo " -d show dir";
echo " -m start midnight commander shell";
echo " -e {editor}, start {editor} of your choice";
return
}

#
# Main procedure start here
#
# Check for sufficent args
#

if [ $# -eq 0 ] ; then
print_help_uu
exit 1
fi

#
# Now parse command line arguments
#
while getopts cdme: opt
do
case "$opt" in
c) cls;;
d) show_ls;;
m) start_mc;;
e) thised="$OPTARG"; start_ed $thised ;;
?) print_help_uu; exit 1;;
esac
done

#
#



#!/bin/bash
#
#
#
#
# Q15
#

temph=`date | cut -c12-13`
dat=`date +"%A %d in %B of %Y (%r)"`

if [ $temph -lt 12 ]
then
mess="Good Morning $LOGNAME, Have nice day!"
fi

if [ $temph -gt 12 -a $temph -le 16 ]
then
mess="Good Afternoon $LOGNAME"
fi

if [ $temph -gt 16 -a $temph -le 18 ]
then
mess="Good Evening $LOGNAME"
fi

if which dialog > /dev/null
then
dialog --backtitle "Linux Shell Script Tutorial"
--title "(-: Welcome to Linux :-)"
--infobox "n$messnThis is $dat" 6 60
echo -n " Press a key to continue. . .
"
read
clear
else
echo -e "$messnThis is $dat"
fi

#
#



#!/bin/bash
#
#
#
#
# Q16
# echo command with escape sequance to give differnt effects
#
# Syntax: echo -e "escape-code your message, var1, var2 etc"
# For eg. echo -e "033[1m Hello World"
# | |
# | |
# Escape code Message
#

clear
echo -e "033[1m Hello World"
# bold effect
echo -e "033[5m Blink"
# blink effect
# back to noraml

# Red color
# Green color
# See remaing on screen

echo -e -n "033[0m "
# back to noraml


# back to noraml
#
#



#!/bin/bash
#
#
#
#
# Q17
# To run type at $ promot as
# $ q17 &
#

echo
echo "Digital Clock for Linux"
echo "To stop this clock use command kill pid, see above for pid"
echo "Press a key to continue. . ."

while :
do
ti=`date +"%r"`
echo -e -n "033[7s" #save current screen postion & attributes
#
# Show the clock
#

tput cup 0 69 # row 0 and column 69 is used to show clock

echo -n $ti # put clock on screen

echo -e -n "033[8u" #restore current screen postion & attributs
#
#Delay fro 1 second
#
sleep 1
done

#
#



#!/bin/bash
#
#
#
#

show_datetime()
{
dialog --backtitle "Linux Shell Tutorial" --title "System date and Time" --infobox
"Date is `date`" 3 40
read
return
}

show_cal()
{
cal > menuchoice.temp.$$
dialog --backtitle "Linux Shell Tutorial" --title "Calender" --infobox "`cat
menuchoice.temp.$$`" 9 25
read
rm -f menuchoice.temp.$$
return
}

delete_file()
{
dialog --backtitle "Linux Shell Tutorial" --title "Delete file"
--inputbox "Enter directory path (Enter for Current Directory)"
10 40 2>/tmp/dirip.$$
rtval=$?

case $rtval in
1) rm -f /tmp/dirip.$$ ; return ;;
255) rm -f /tmp/dirip.$$ ; return ;;
esac

mfile=`cat /tmp/dirip.$$`

if [ -z $mfile ]
then
mfile=`pwd`/*
else
grep "*" /tmp/dirip.$$
if [ $? -eq 1 ]
then
mfile=$mfile/*
fi
fi

for i in $mfile
do
if [ -f $i ]
then
echo "$i Delete?" >> /tmp/finallist.$$
fi
done



dialog --backtitle "Linux Shell Tutorial" --title "Select File to Delete"
--menu "Use [Up][Down] to move, [Enter] to select file"
20 60 12 `cat /tmp/finallist.$$` 2>/tmp/file2delete.tmp.$$

rtval=$?

file2erase=`cat /tmp/file2delete.tmp.$$`

case $rtval in
0) dialog --backtitle "Linux Shell Tutorial" --title "Are you shur"
--yesno "nnDo you want to delete : $file2erase " 10 60

if [ $? -eq 0 ] ; then
rm -f $file2erase
if [ $? -eq 0 ] ; then
dialog --backtitle "Linux Shell Tutorial"
--title "Information: Delete Command" --infobox "File: $file2erase is
Sucessfully deleted,Press a key" 5 60
read
else
--title "Error: Delete Command" --infobox "Error deleting File: $file2erase,
Press a key" 5 60
read
fi
else
--title "Information: Delete Command" --infobox "File: $file2erase is not
deleted, Action is canceled, Press a key" 5 60
read
fi
;;
1) rm -f /tmp/dirip.$$ ; rm -f /tmp/finallist.$$ ;
rm -f /tmp/file2delete.tmp.$$; return;;
255) rm -f /tmp/dirip.$$ ; rm -f /tmp/finallist.$$ ;
rm -f /tmp/file2delete.tmp.$$; return;;
esac
rm -f /tmp/dirip.$$
rm -f /tmp/finallist.$$
rm -f /tmp/file2delete.tmp.$$
return
}

while true
do
dialog --clear --title "Main Menu"
--menu "To move [UP/DOWN] arrow keys n
[Enter] to Selectn
Choose the Service you like:" 20 51 4
"Date/time" "To see System Date & Time"
"Calender" "To see Calaender"
"Delete" "To remove file"
"Exit" "To exit this Program" 2> menuchoice.temp.$$

retopt=$?

choice=`cat menuchoice.temp.$$`

rm -f menuchoice.temp.$$



case $retopt in
0)
case $choice in
Date/time) show_datetime ;;
Calender) show_cal ;;
Delete) delete_file ;;
Exit) exit 0;;
esac
;;
1) exit ;;
255) exit ;;
esac
done
clear

#
#



#!/bin/bash
#
#
#
#
# Q19
#

nouser=`who | wc -l`
echo -e "User name: $USER (Login name: $LOGNAME)" >> /tmp/info.tmp.01.$$$
echo -e "Current Shell: $SHELL" >> /tmp/info.tmp.01.$$$
echo -e "Home Directory: $HOME" >> /tmp/info.tmp.01.$$$
echo -e "Your O/s Type: $OSTYPE" >> /tmp/info.tmp.01.$$$
echo -e "PATH: $PATH" >> /tmp/info.tmp.01.$$$
echo -e "Current directory: `pwd`" >> /tmp/info.tmp.01.$$$
echo -e "Currently Logged: $nouser user(s)" >> /tmp/info.tmp.01.$$$

if [ -f /etc/redhat-release ]
then
echo -e "OS: `cat /etc/redhat-release`" >> /tmp/info.tmp.01.$$$
fi

if [ -f /etc/shells ]
then
echo -e "Available Shells: " >> /tmp/info.tmp.01.$$$
echo -e "`cat /etc/shells`" >> /tmp/info.tmp.01.$$$
fi

if [ -f /etc/sysconfig/mouse ]
then
echo -e "--------------------------------------------------------------------" >>
/tmp/info.tmp.01.$$$
echo -e "Computer Mouse Information: " >> /tmp/info.tmp.01.$$$
echo -e "--------------------------------------------------------------------" >>
echo -e "`cat /etc/sysconfig/mouse`" >> /tmp/info.tmp.01.$$$
fi
echo -e "--------------------------------------------------------------------" >>
echo -e "Computer CPU Information:" >> /tmp/info.tmp.01.$$$
echo -e "--------------------------------------------------------------------" >>
cat /proc/cpuinfo >> /tmp/info.tmp.01.$$$

echo -e "--------------------------------------------------------------------" >>
echo -e "Computer Memory Information:" >> /tmp/info.tmp.01.$$$
echo -e "--------------------------------------------------------------------" >>
cat /proc/meminfo >> /tmp/info.tmp.01.$$$

if [ -d /proc/ide/hda ]
then
echo -e "--------------------------------------------------------------------" >>
echo -e "Hard disk information:" >> /tmp/info.tmp.01.$$$
echo -e "--------------------------------------------------------------------" >>



echo -e "Model: `cat /proc/ide/hda/model` " >> /tmp/info.tmp.01.$$$
echo -e "Driver: `cat /proc/ide/hda/driver` " >> /tmp/info.tmp.01.$$$
echo -e "Cache size: `cat /proc/ide/hda/cache` " >> /tmp/info.tmp.01.$$$
fi
echo -e "--------------------------------------------------------------------" >>
echo -e "File System (Mount):" >> /tmp/info.tmp.01.$$$
echo -e "--------------------------------------------------------------------" >>
cat /proc/mounts >> /tmp/info.tmp.01.$$$

if which dialog > /dev/null
then
dialog --backtitle "Linux Software Diagnostics (LSD) Shell Script Ver.1.0" --title
"Press Up/Down Keys to move" --textbox /tmp/info.tmp.01.$$$ 21 70
else
cat /tmp/info.tmp.01.$$$ |more
fi

rm -f /tmp/info.tmp.01.$$$

#
#


http://www.cyberciti.biz/pdf/lsst/scripts/for2

#!/bin/bash
#
#
#
#

echo "Can you see the following:"

for (( i=1; i<=5; i++ ))
do
for (( j=1; j<=i; j++ ))
do
echo -n "$i"
done
echo ""
done

#
#

http://www.cyberciti.biz/pdf/lsst/scripts/for2 [7/29/2002 6:56:20 PM]


#!/bin/bash
#
#
#
#

echo "Can you see the following:"

for (( i=1; i<=5; i++ ))
do
for (( j=1; j<=i; j++ ))
do
echo -n "$j"
done
echo ""
done

#
#



#!/bin/bash
#
#
#
#

echo "Climb the steps of success"

for (( i=1; i<=5; i++ ))
do
for (( j=1; j<=i; j++ ))
do
echo -n " |"
done
echo "_ "
done

#
#



#!/bin/bash
#
#
#
#

echo "Stars"

for (( i=1; i<=5; i++ ))
do
for (( j=1; j<=i; j++ ))
do
echo -n " *"
done
echo ""
done

#
#



#!/bin/bash
#
#
#
#

echo "Stars"

for (( i=1; i<=5; i++ ))
do
for (( j=1; j<=i; j++ ))
do
echo -n " *"
done
echo ""
done

for (( i=5; i>=1; i-- ))
do
for (( j=1; j<=i; j++ ))
do
echo -n " *"
done
echo ""
done

#
#



#!/bin/bash
#
#
#
#

clear

for (( i=1; i<=3; i++ ))
do
for (( j=1; j<=i; j++ ))
do
echo -n "|Linux"
done
echo "______"
done

for (( i=3; i>=1; i-- ))
do
for (( j=1; j<=i; j++ ))
do
echo -n "|Linux"
done

if [ $i -eq 3 ]; then
echo -n "______"
echo -n -e ">> Powerd Server.n"
else
echo "~~~~~"
fi
done

#
#



#!/bin/bash
#
#
#
#

MAX_NO=0

echo -n "Enter Number between (5 to 9) : "
read MAX_NO

if ! [ $MAX_NO -ge 5 -a $MAX_NO -le 9 ] ; then
echo "I ask to enter number between 5 and 9, Okay"
exit 1
fi

clear

for (( i=1; i<=MAX_NO; i++ ))
do
for (( s=MAX_NO; s>=i; s-- ))
do
echo -n " "
done
for (( j=1; j<=i; j++ ))
do
echo -n " $i"
done
echo ""
done

for (( i=1; i<=MAX_NO; i++ ))
do
do
echo -n " "
done
for (( j=1; j<=i; j++ ))
do
echo -n " ."
done
echo ""
done

echo -e "nntttI hope you like it my stupidity (?)"

#
#



#!/bin/bash
#
#
#
#

MAX_NO=0

echo -n "Enter Number between (5 to 9) : "
read MAX_NO

if ! [ $MAX_NO -ge 5 -a $MAX_NO -le 9 ] ; then
echo "I ask to enter number between 5 and 9, Okay"
exit 1
fi

clear

for (( i=1; i<=MAX_NO; i++ ))
do
do
echo -n " "
done
for (( j=1; j<=i; j++ ))
do
echo -n " ."
done
echo ""
done
###### Second stage ######################
##
##
for (( i=MAX_NO; i>=1; i-- ))
do
for (( s=i; s<=MAX_NO; s++ ))
do
echo -n " "
done
for (( j=1; j<=i; j++ ))
do
echo -n " ."
done
echo ""
done

echo -e "nntttI hope you like it my stupidity (?)"

#
#


http://www.cyberciti.biz/pdf/lsst/images/forloop/for7.jpg

http://www.cyberciti.biz/pdf/lsst/images/forloop/for7.jpg [7/29/2002 6:57:09 PM]

http://www.cyberciti.biz/pdf/lsst/images/forloop/for8-b.jpg

http://www.cyberciti.biz/pdf/lsst/images/forloop/for8-b.jpg [7/29/2002 6:57:17 PM]

http://www.cyberciti.biz/pdf/lsst/scripts/rename.awk

# Linux Shell Scripting Tutorial v1.05r3, Summer-2002
# rename.awk : awk script to rename file with some builtin Intelligence
# Author : Vivek G. Gite <vivek@nixcraft.com>
#
BEGIN{
}

#
#
{
isdir1 = "[ -d " $1 " ] "
isdir2 = "[ -d " $2 " ] "

scriptname = "up2low"
awkscriptname = "rename.awk"

sfile = $1
dfile = $2
#
# we are not suppose to rename dirs in source or destination
#

#
# make sure we are renaming our self if in same dir
#
if ( sfile == scriptname || sfile == awkscriptname )
next
else if( ( system(isdir1) ) == 0 || system((isdir2)) == 0 )
{
printf "%s or %s is directory can't rename it to lower casen",sfile,dfile
next # continue with next recored
}
else if ( sfile == dfile )
{
printf "Skiping, "%s" is alrady in lowercasen",sfile
next
}
else # everythink is okay rename it to lowercase
{
mvcmd = "mv " sfile " " dfile
printf "Renaming %s to %sn",sfile,dfile
system(mvcmd)
}
}

#
#
END{
}

#
#

http://www.cyberciti.biz/pdf/lsst/scripts/rename.awk [7/29/2002 6:57:29 PM]

http://www.cyberciti.biz/pdf/lsst/scripts/up2low

#!/bin/bash
#
# up2low : script to convert upercase filename to lowercase in current
# working dir
# Author : Vivek G. Gite <vivek@nixcraft.com>
#
#Copy this file to your bin directory i.e. $HOME/bin as cp rename.awk $HOME/bin
#

AWK_SCRIPT="rename.awk"

#
# change your location here
#
awkspath=$HOME/bin/$AWK_SCRIPT

ls -1 > /tmp/file1.$$

tr "[A-Z]" "[a-z]" < /tmp/file1.$$ > /tmp/file2.$$

paste /tmp/file1.$$ /tmp/file2.$$ > /tmp/tmpdb.$$

rm -f /tmp/file1.$$
rm -f /tmp/file2.$$

#
# Make sure awk script exist
#

if [ -f $awkspath ]; then
awk -f $awkspath /tmp/tmpdb.$$
else
echo -e "n$0: Fatal error - $awkspath not found"
echo -e "nMake sure $awkspath is set correctly in $0 scriptn"
fi

rm -f /tmp/tmpdb.$$

#
#

http://www.cyberciti.biz/pdf/lsst/scripts/up2low [7/29/2002 6:57:32 PM]

Linux Shell Scripting Tutorial v1.05r3 > Misc. Linux/Unix definition

Note: This file is part of Linux Shell Scripting Tutorial, and contains many Linux/Unix definition,
miscellaneous concepts and answer to many shell scripts exercise section.

Free
Linux is free.
First ,It's available free of cost (You don't have to pay to use this OS, other OSes like MS-Windows or
Commercial version of Unix may cost you money)
Second free means freedom to use Linux, i.e. when you get Linux you will also get source code of Linux,
so you can modify OS (Yes OS! Linux OS!!) according to your taste.
It also offers many Free Software applications, programming languages, and development tools etc. Most
of the Program/Software/OS are under GNU General Public License (GPL).

Unix Like
Unix is almost 35 year old Os.
In 1964 OS called MULTICS (Multiplexed Information and Computing System) was developed by Bell
Labs, MIT & General Electric. But this OS was not the successful one.

Then Ken Thompson (System programmer of Bell Labs) thinks he could do better (In 1991, Linus
Torvalds felt he could do better than Minix - History repeats itself.). So Ken Thompson wrote OS on
PDP - 7 Computer, assembler and few utilities, this is know as Unix (1969). But this version of Unix is
not portable. Then Unix was rewrote in C. Because Unix written in 'C', it is portable. It means Unix can
run on verity of Hardware platform (1970-71).
At the same time Unix was started to be distribute to Universities. There students and professor started
more experiments on Unix. Because of this Unix gain more popularity, also several new features are
added to Unix. Then US govt. & military used Unix for there inter-network (now it is know as
INTERNET).
So Unix is Multi-user, Multitasking, Internet-aware Network OS. Linux almost had same Unix Like
feature for e.g.
q Like Unix, Linux is also written in C.

q Like Unix, Linux is also the Multi-user/Multitasking/32 or 64 bit Network OS.

q Like Unix, Linux is rich in Development/Programming environment.

q Like Unix, Linux runs on different hardware platform; for e.g.

r Intel x86 processor (Celeron/PII/PIII/PIV/Old-Pentiums/80386/80486)

r Macintosh PC's

http://www.cyberciti.biz/pdf/lsst/misc.htm (1 of 12) [7/29/2002 6:58:21 PM]


r Cyrix processor
r AMD processor
r Sun Microsystems Sparc processor
r Alpha Processor (Compaq)

Open Source
Linux is developed under the GNU Public License. This is sometimes referred to as a "copyleft", to
distinguish it from a copyright.
Under GPL the source code is available to anyone who wants it, and can be freely modified, developed,
and so forth. There are only a few restrictions on the use of the code. If you make changes to the
programs , you have to make those changes available to everyone. This basically means you can't take
the Linux source code, make a few changes, and then sell your modified version without making the
source code available. For more details, please visit the open-source home page.

Common vi editor command list
For this Purpose Use this vi Command Syntax
To insert new text esc + i ( You have to press 'escape' key then 'i')
esc + : + w (Press 'escape' key then 'colon' and
To save file
finally 'w')
To save file with file name (save as) esc + : + w "filename"
To quit the vi editor esc + : + q
To quit without saving esc + : + q!
To save and quit vi editor esc + : + wq
esc + /word (Press 'escape' key, type /word-to-find,
To search for specified word in forward direction for e.g. to find word 'shri', type as
/shri)
To continue with search n
To search for specified word in backward direction esc + ?word (Press 'escape' key, type word-to-find)
To copy the line where cursor is located esc + yy
To paste the text just deleted or copied at the cursor esc + p
To delete entire line where cursor is located esc + dd
To delete word from cursor position esc + dw
esc + :$s/word-to-find/word-to-replace/g
To Find all occurrence of given word and Replace For. e.g. :$s/mumbai/pune/g
then globally without confirmation Here word "mumbai" is replace with "pune"



To Find all occurrence of given word and Replace
esc + :$s/word-to-find/word-to-replace/cg
then globally with confirmation
esc + :!shell-command
To run shell command like ls, cp or date etc within
vi
For e.g. :!pwd

How Shell Locates the file
To run script, you need to have in the same directory where you created your script, if you are in
different directory your script will not run (because of path settings), For e.g.. Your home directory is (
use $ pwd to see current working directory) /home/vivek. Then you created one script called 'first', after
creation of this script you moved to some other directory lets say /home/vivek/Letters/Personal, Now if
you try to execute your script it will not run, since script 'first' is in /home/vivek directory, to overcome
this problem there are two ways first, specify complete path of your script when ever you want to run it
from other directories like giving following command
$ /bin/sh /home/vivek/first

Now every time you have to give all this detailed as you work in other directory, this take time and you
have to remember complete path.
There is another way, if you notice that all of our programs (in form of executable files) are marked as
executable and can be directly executed from prompt from any directory. (To see executables of our
normal program give command $ ls -l /bin ) By typing commands like
$ bc
$ cc myprg.c
$ cal
etc, How its possible? All our executables files are installed in directory called /bin and /bin directory is
set in your PATH setting, Now when you type name of any command at $ prompt, what shell do is it first
look that command in its internal part (called as internal command, which is part of Shell itself, and
always available to execute), if found as internal command shell will execute it, If not found It will look
for current directory, if found shell will execute command from current directory, if not found, then Shell
will Look PATH setting, and try to find our requested commands executable file in all of the directories
mentioned in PATH settings, if found it will execute it, otherwise it will give message "bash: xxxx
:command not found", Still there is one question remain can I run my shell script same as these
executables?, Yes you can, for this purpose create bin directory in your home directory and then copy



your tested version of shell script to this bin directory. After this you can run you script as executable file
without using command like
$ /bin/sh /home/vivek/first
Command to create you own bin directory.
$ cd
$ mkdir bin
$ cp first ~/bin
$ first

Each of above commands can be explained as follows:
Each of above command Explanation
$ cd Go to your home directory
Now created bin directory, to install your own shell
$ mkdir bin script, so that script can be run as independent
program or can be accessed from any directory
$ cp first ~/bin copy your script 'first' to your bin directory
$ first Test whether script is running or not (It will run)

Answer to Variable sections exercise
Q.1.How to Define variable x with value 10 and print it on screen.
$ x=10
$ echo $x

Q.2.How to Define variable xn with value Rani and print it on screen
For Ans. Click here
$ xn=Rani
$ echo $xn

Q.3.How to print sum of two numbers, let's say 6 and 3
$ echo 6 + 3
This will print 6 + 3, not the sum 9, To do sum or math operations in shell use expr, syntax is as follows
Syntax: expr op1 operator op2
Where, op1 and op2 are any Integer Number (Number without decimal point) and operator can be
+ Addition
- Subtraction
/ Division
% Modular, to find remainder For e.g. 20 / 3 = 6 , to find remainder 20 % 3 = 2, (Remember its integer
calculation)
* Multiplication
$ expr 6 + 3



Now It will print sum as 9 , But
$ expr 6+3
will not work because space is required between number and operator (See Shell Arithmetic)

Q.4.How to define two variable x=20, y=5 and then to print division of x and y (i.e. x/y)
For Ans. Click here
$x=20
$ y=5
$ expr x / y

Q.5.Modify above and store division of x and y to variable called z
For Ans. Click here
$ x=20
$ y=5
$ z=`expr x / y`
$ echo $z
Q.6.Point out error if any in following script
$ vi variscript
#
#
# Script to test MY knolwdge about variables!
#
myname=Vivek
myos = TroubleOS -----> ERROR 1
myno=5
echo "My number is myno, can you see this number" ----> ERROR 2
ERROR 1 Read this
ERROR 2 Read this

Following script should work now, after bug fix!
$ vi variscript
#
#
# Script to test MY knolwdge about variables!
#
myname=Vivek
myos=TroubleOS
myno=5
echo "My number is $myno, can you see this number"



Parameter substitution.
Now consider following command
$($ echo 'expr 6 + 3')
The command ($ echo 'expr 6 + 3') is know as Parameter substitution. When a command is enclosed
in backquotes, the command get executed and we will get output. Mostly this is used in conjunction with
other commands. For e.g.
$pwd
$cp /mnt/cdrom/lsoft/samba*.rmp `pwd`

Now suppose we are working in directory called "/home/vivek/soft/artical/linux/lsst" and I want to copy
some samba files from "/mnt/cdrom/lsoft" to my current working directory, then my command will be
something like
$cp /mnt/cdrom/lsoft/samba*.rmp /home/vivek/soft/artical/linux/lsst
Instead of giving above command I can give command as follows
Here file is copied to your working directory. See the last Parameter substitution of `pwd` command,
expand it self to /home/vivek/soft/artical/linux/lsst. This will save my time.

Future Point: What is difference between following two command?

AND

$cp /mnt/cdrom/lsoft/samba*.rmp .

Try to note down output of following Parameter substitution.
$echo "Today date is `date`"
$cal > menuchoice.temp.$$
$dialog --backtitle "Linux Shell Tutorial" --title "Calender" --infobox "`cat
menuchoice.temp.$$`" 9 25 ; read



Answer to if command.
A) There is file called foo, on your disk and you give command, $ ./trmfi foo what will be output.
Ans.: foo file will be deleted, and message "foo file deleted" on screen will be printed.
B) If bar file not present on your disk and you give command, $ ./trmfi bar what will be output.
Ans.: Message "rm: cannot remove `bar': No such file or directory" will be printed because bar file does
not exist on disk and we have called rm command, so error from rm commad
C) And if you type $ ./trmfi, What will be output.
Ans.: Following message will be shown by rm command, because rm is called from script without any
parameters.
rm: too few arguments
Try `rm --help' for more information.

Answer to Variables in Linux.
1) If you want to print your home directory location then you give command:
(a) $ echo $HOME
or
(b) $ echo HOME
Which of the above command is correct & why?
Ans.: (a) command is correct, since we have to print the contains of variable (HOME) and not the
HOME. You must use $ followed by variable name to print variables cotaines.

Answer to Process Section.
1) Is it example of Multitasking?
Ans.: Yes, since you are running two process simultaneously.
2) How you will you find out the both running process (MP3 Playing & Letter typing)?
Ans.: Try $ ps aux or $ ps ax | grep process-you-want-to-search
3) "Currently only two Process are running in your Linux/PC environment", Is it True or False?, And
how you will verify this?
Ans.: No its not true, when you start Linux Os, various process start in background for different purpose.
To verify this simply use top or ps aux command.
4) You don't want to listen music (MP3 Files) but want to continue with other work on PC, you will take
any of the following action:
1. Turn off Speakers



2. Turn off Computer / Shutdown Linux Os
3. Kill the MP3 playing process
4. None of the above
Ans.: Use action no. 3 i.e. kill the MP3 process.
Tip: First find the PID of MP3 playing process by issuing command:
$ ps ax | grep mp3-process-name
Then in the first column you will get PID of process. Kill this PID to end the process as:
$ kill PID
Or you can try killall command to kill process by name as follows:
$ killall mp3-process-name

Linux Console (Screen)
How can I write colorful message on Linux Console? , mostly this kind of question is asked by
newcomers (Specially those who are learning shell programming!). As you know in Linux everything is
considered as a file, our console is one of such special file. You can write special character sequences to
console, which control every aspects of the console like Colors on screen, Bold or Blinking text effects,
clearing the screen, showing text boxes etc. For this purpose we have to use special code called escape
sequence code. Our Linux console is based on the DEC VT100 serial terminals which support ANSI
escape sequence code.
What is special character sequence and how to write it to Console?
By default what ever you send to console it is printed as its. For e.g. consider following echo statement,
$ echo "Hello World"
Hello World
Above echo statement prints sequence of character on screen, but if there is any special escape sequence
(control character) in sequence , then first some action is taken according to escape sequence (or control
character) and then normal character is printed on console. For e.g. following echo command prints
message in Blue color on console
$ echo -e "033[34m Hello Colorful World!"
Hello Colorful World!

Above echo statement uses ANSI escape sequence (033[34m), above entire string ( i.e. "033[34m
Hello Colorful World!" ) is process as follows
1) First 033, is escape character, which causes to take some action
2) Here it set screen foreground color to Blue using [34m escape code.
3) Then it prints our normal message Hello Colorful World! in blue color.
Note that ANSI escape sequence begins with 033 (Octal value) which is represented as ^[ in termcap
and terminfo files of terminals and documentation.
You can use echo statement to print message, to use ANSI escape sequence you must use -e option



(switch) with echo statement, general syntax is as follows
Syntax
echo -e "033[escape-code your-message"
In above syntax you have to use033[ as its with different escape-code for different operations. As soon
as console receives the message it start to process/read it, and if it found escape character (033) it moves
to escape mode, then it read "[" character and moves into Command Sequence Introduction (CSI)
mode. In CSI mode console reads a series of ASCII-coded decimal numbers (know as parameter) which
are separated by semicolon (;) . This numbers are read until console action letter or character is not found
(which determines what action to take). In above example
033 Escape character
[ Start of CSI
34 34 is parameter
m m is letter (specifies action)

Following table show important list of such escape-code/action letter or character
Character or letter Use in CSI Examples
h Set the ANSI mode echo -e "033[h"
l Clears the ANSI mode echo -e "033[l"
Useful to show characters in
different colors or effects such as
m echo -e "033[35m Hello World"
BOLD and Blink, see below for
parameter taken by m.
Turns keyboard num lock, caps
q lock, scroll lock LED on or off, see echo -e "033[2q"
below.
Stores the current cursor x,y
s position (col , row position) and echo -e "033[7s"
attributes
Restores cursor position and
u echo -e "033[8u"
attributes

m understand following parameters
Parameter Meaning Example
Sets default color scheme
(White foreground and Black
0
background), normal intensity,
no blinking etc.
$ echo -e "I am 033[1m BOLD 033[0m Person"
I am BOLD Person
1 Set BOLD intensity
Prints BOLD word in bold intensity and next ANSI
Sequence remove bold effect (033[0m)



2 Set dim intensity $ echo -e "033[1m BOLD 033[2m DIM 033[0m"
5 Blink Effect $ echo -e "033[5m Flash! 033[0m"
Reverse video effect i.e. Black
foreground and white
7 $ echo -e "033[7m Linux OS! Best OS!! 033[0m"
background in default color
scheme
Shows special control
character as graphics
character. For e.g. Before
issuing this command press alt $ press alt + 178
key (hold down it) from $ echo -e "033[11m"
numeric key pad press 178 $ press alt + 178
11
and leave both key; nothing $ echo -e "033[0m"
will be printed. Now give --> $ press alt + 178
command shown in example
and try the above, it works.
(Hey you must know extended
ASCII Character for this!!!)
25 Removes/disables blink effect
Removes/disables reverse
27
effect
Set foreground color
31 - RED
30 - 37 32 - Green $ echo -e "033[31m I am in Red"
xx - Try to find yourself this
left as exercise for you :-)
Set background color
40 - 47 xx - Try to find yourself this $ echo -e "033[44m Wow!!!"
left as exercise for you :-)

q understand following parameters
Parameters Meaning
0 Turns off all LEDs on Keyboard
1 Scroll lock LED on and others off
2 Num lock LED on and others off
3 Caps lock LED on and others off

Click here to see example of q command.

Click here to see example of m command.

Click here to see example of s and u command.



This is just quick introduction about Linux Console and what you can do using this Escape sequence.
Above table does not contains entire CSI sequences. My up-coming tutorial series on C Programming
Language will defiantly have entire story with S-Lang and curses (?). What ever knowledge you gain
here will defiantly first step towards the serious programming using c. This much knowledge is sufficient
for Shell Programming, now try the following exercise :-) I am Hungry give me More Programming
Exercise & challenges! :-)

1) Write function box(), that will draw box on screen (In shell Script)
box (left, top, height, width)
For e.g. box (20,5,7,40)

Hint: Use ANSI Escape sequence
1) Use of 11 parameter to m
2) Use following for cursor movement
row;col H
or
rowl;col f

For e.g.
$ echo -e "033[5;10H Hello"
$ echo -e "033[6;10f Hi"
In Above example prints Hello message at row 5 and column 6 and Hi at 6th row and 10th Column.



Shell Built in Variables
Shell Built in
Meaning
Variables

Number of command line arguments. Useful to test no. of command
$#
line args in shell script.

$* All arguments to shell
$@ Same as above
$- Option supplied to shell
$$ PID of shell

$! PID of last started background process (started with &)

See example of $@ and $* variable.


http://www.cyberciti.biz/pdf/lsst/scripts/dial

dialog --title "Linux Dialog Utility Infobox" --backtitle "Linux Shell Script
Tutorial" --infobox "This is dialog box called infobox, which is used
to show some information on screen, Thanks to Savio Lam and
Stuart Herbert to give us this utility. Press any key. . . " 7 50 ; read

#
#

http://www.cyberciti.biz/pdf/lsst/scripts/dial [7/29/2002 7:02:05 PM]

http://www.cyberciti.biz/pdf/lsst/scripts/dia2

dialog --title "Linux Dialog Utility Msgbox" --backtitle "Linux Shell Script
Tutorial" --msgbox "This is dialog box called msgbox, which is used
to show some information on screen which has also Ok button, Thanks to Savio Lam
and Stuart Herbert to give us this utility. Press any key. . . " 9 50

#
#

http://www.cyberciti.biz/pdf/lsst/scripts/dia2 [7/29/2002 7:02:19 PM]


dialog --title "Alert : Delete File" --backtitle "Linux Shell Script
Tutorial" --yesno "nDo you want to delete '/usr/letters/jobapplication'
file" 7 60
sel=$?
case $sel in
0) echo "User select to delete file";;
1) echo "User select not to delete file";;
255) echo "Canceled by user by pressing [ESC] key";;
esac

#
#



dialog --title "Inputbox - To take input from you" --backtitle "Linux Shell
Script Tutorial" --inputbox "Enter your name please" 8 60 2>/tmp/input.$$

sel=$?

na=`cat /tmp/input.$$`
case $sel in
0) echo "Hello $na" ;;
1) echo "Cancel is Press" ;;
255) echo "[ESCAPE] key pressed" ;;
esac

rm -f /tmp/input.$$

#
#


http://www.cyberciti.biz/pdf/lsst/scripts/smenu

#
#How to create small menu using dialog
#
dialog --backtitle "Linux Shell Script Tutorial " --title "Main
Menu" --menu "Move using [UP] [DOWN],[Enter] to
Select " 15 50 3
Date/time "Shows Date and Time"
Editor "To start vi editor " 2>/tmp/menuitem.$$

menuitem=`cat /tmp/menuitem.$$`

opt=$?

case $menuitem in
Date/time) date;;
Calendar) cal;;
Editor) vi;;
esac

#
#

http://www.cyberciti.biz/pdf/lsst/scripts/smenu [7/29/2002 7:02:50 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/sname

11 Vivek
12 Renuka
13 Prakash
14 Ashish
15 Rani

http://www.cyberciti.biz/pdf/lsst/datafiles/sname [7/29/2002 7:03:02 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/smark

11 67
12 55
13 96
14 36
15 67

http://www.cyberciti.biz/pdf/lsst/datafiles/smark [7/29/2002 7:03:06 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/inventory

egg order 4
cacke good 10
cheese okay 4
pen good 12
Floppy good 5

http://www.cyberciti.biz/pdf/lsst/datafiles/inventory [7/29/2002 7:03:20 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/teaormilk

tea Red-Lable is good.
tea is better than the coffee.

http://www.cyberciti.biz/pdf/lsst/datafiles/teaormilk [7/29/2002 7:03:31 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/personame

Hello I am vivek
12333
12333
welcome
to

http://www.cyberciti.biz/pdf/lsst/datafiles/personame [7/29/2002 7:03:41 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/demo-file

hello world!
cartoons are good
what
the number one song
12221
they love us
I too

http://www.cyberciti.biz/pdf/lsst/datafiles/demo-file [7/29/2002 7:03:53 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/demofile

Hello World.

I love linux.

Linux is cooool.



Do you know?

Okay! I will stop.

http://www.cyberciti.biz/pdf/lsst/datafiles/demofile [7/29/2002 7:04:03 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/inven

1. Pen 5 20.00
2. Pencil 10 2.00
3. Rubber 3 3.50
4. Cock 2 45.50

http://www.cyberciti.biz/pdf/lsst/datafiles/inven [7/29/2002 7:04:29 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/math

{
print $1 " + " $2 " = " $1 + $2
print $1 " - " $2 " = " $1 - $2
print $1 " / " $2 " = " $1 / $2
print $1 " x " $2 " = " $1 * $2
print $1 " mod " $2 " = " $1 % $2
}

http://www.cyberciti.biz/pdf/lsst/datafiles/math [7/29/2002 7:04:49 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/math1

{
no1 = $1
no2 = $2
ans = $1 + $2
print no1 " + " no2 " = " ans
}

http://www.cyberciti.biz/pdf/lsst/datafiles/math1 [7/29/2002 7:04:59 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/bill

{
total = $3 * $4
recno = $1
item = $2
}

http://www.cyberciti.biz/pdf/lsst/datafiles/bill [7/29/2002 7:05:03 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/bill2

BEGIN {
print "---------------------------"
print "Bill for the 4-March-2001. "
print "By Vivek G Gite. "
print "---------------------------"
}
{
total = $3 * $4
recno = $1
item = $2
gtotal += total
}

END {
print "---------------------------"
print "Total Rs." gtotal
print "==========================="
}

http://www.cyberciti.biz/pdf/lsst/datafiles/bill2 [7/29/2002 7:05:11 PM]


BEGIN {
printf "---------------------------n"
}
{
total = $3 * $4
recno = $1
item = $2
gtotal += total
printf "%d %s Rs.%fn", recno, item, total
#printf "%2d %-10s Rs.%7.2fn", recno, item, total
}

END {
printf "---------------------------n"
printf "Total Rs. %fn" ,gtotal
#printf "tTotal Rs. %7.2fn" ,gtotal
printf "===========================n"
}



BEGIN {
printf "---------------------------n"
}
{
total = $3 * $4
recno = $1
item = $2
gtotal += total
printf "%2d %-10s Rs.%7.2fn", recno, item, total
}

END {
printf "---------------------------n"
printf "tTotal Rs. %6.2fn" ,gtotal
printf "===========================n"
}


http://www.cyberciti.biz/pdf/lsst/datafiles/math2

BEGIN {
}

{
no1 = $1
op = $2
no2 = $3
ans = 0

if ( op == "+" )
{
ans = $1 + $3
}
else
{
printf "Opps!Error I only know how to add.nSyntax: number1 + number2n"
}
}

END {
printf "nGoodbuy %sn" , ENVIRON["USER"]
}

http://www.cyberciti.biz/pdf/lsst/datafiles/math2 [7/29/2002 7:05:56 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/while01.awk

BEGIN{
printf "Press ENTER to continue with for loop example from LSST v1.05r3n"
}
{
sum = 0
i = 1
for (i=1; i<=10; i++)
{
sum += i; # sum = sum + i
}
printf "Sum for 1 to 10 numbers = %d nGoodbuy!nn", sum
exit 1
}

http://www.cyberciti.biz/pdf/lsst/datafiles/while01.awk [7/29/2002 7:06:15 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/filelist.conf


http://www.cyberciti.biz/pdf/lsst/datafiles/filelist.conf [7/29/2002 7:06:30 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/tryrmsys

{
dcmd = "rm " $1
if ( system(dcmd) != 0 )
printf "rm command not successfuln"
else
printf "rm command is successful and %s file is removed n", $1
}

http://www.cyberciti.biz/pdf/lsst/datafiles/tryrmsys [7/29/2002 7:06:39 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/testusrip

BEGIN {
printf "Your name please:"
getline na < "-"
printf "%s your age please:",na
getline age < "-"
print "Hello " na, ", next year you will be " age + 1
}

http://www.cyberciti.biz/pdf/lsst/datafiles/testusrip [7/29/2002 7:06:53 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/awkread_file

BEGIN{
"date" | getline
print $0
}

http://www.cyberciti.biz/pdf/lsst/datafiles/awkread_file [7/29/2002 7:07:03 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/awkread_file1

BEGIN{
"date" | getline today
print today
}

http://www.cyberciti.biz/pdf/lsst/datafiles/awkread_file1 [7/29/2002 7:07:06 PM]

http://www.cyberciti.biz/pdf/lsst/scripts/temp2final1.awk

#
#temp2final1.awk: Version 2
#Linux Shell Scripting Tutorial v1.05, March 2001
#
#Author: Vivek G Gite
#
#
#This version checks for source and destination file first
#then copy the file. If file alrady exist it will ask confirmation.
#
#
#

BEGIN{
}

#
#
{
sfile = $1
dfile = $2
issexist = "[ -e " $1 " ]"
isdexist = "[ -e " $2 " ]"
cpcmd = "cp " $1 " " $2
printf "Coping %s to %sn",sfile,dfile
if( ( system(issexist) ) != 0 )
{
printf "Skipking "%s", does not existn",sfile
next # read next record
}

if ( ( system(isdexist) ) == 0)
{
printf ""%s", exist overwrite(y/N)?", sfile
getline ans < "-"
if( ans == "y" || ans == "Y")
system(cpcmd)
}
else
system(cpcmd)
}

#
#
END{
}
#
#

http://www.cyberciti.biz/pdf/lsst/scripts/temp2final1.awk [7/29/2002 7:07:15 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/demofile1

Hello World.

I love linux.

Linux is cooool.



Do you know?

Okay! I will stop.

I care for you and
Vivek care for.
1224
welcome
6888
linux liux
linux is linux

http://www.cyberciti.biz/pdf/lsst/datafiles/demofile1 [7/29/2002 7:07:28 PM]

http://www.cyberciti.biz/pdf/lsst/datafiles/chg1.sed

1i
/Pen/s/20.00/19.5/
/Pencil/s/2.00/2.60/
/Rubber/s/3.50/4.25/
/Cock/s/45.50/51.00/

http://www.cyberciti.biz/pdf/lsst/datafiles/chg1.sed [7/29/2002 7:07:44 PM]


Todays date is 5-12-01 i.e. 5-Dec-2001
********
My brother Vivkran was born on 5-Dec-70
My birthdate : April 5, 00
*****
Renu my sister was born on 6-1-74
Numbers fun Binary numbers
************************
1001
100001
10001
1000000001
10101010
10101010
***
Okay Linux is just like a star.

Star brings good things to life

When I was little kid
I love to see star, my mother says star are Gods Gift to Us!

Is their any relation between star and Linux
***


http://www.cyberciti.biz/pdf/lsst/datafiles/dem_gsed

/^*{2,3}$/,/^*{2,3}$/{
/^$/d
s/Linux/Linux-Unix/
}

http://www.cyberciti.biz/pdf/lsst/datafiles/dem_gsed [7/29/2002 7:08:01 PM]


Welcome to world of sed what sed is?

I don't know what sed is but I think

Rani knows what sed Is
---------------------------------------------------


http://www.cyberciti.biz/pdf/lsst/datafiles/friends

-----------------------------------------------------------------------
Name of Friend DOB Hobby Phone #
-----------------------------------------------------------------------
V.K. Rajopadhey 5/12/73 Food, Music 98220-5678
5/22,Stree 4,
A'bad,MH, INDIA.

A.G. Gite 15/6/72 Computers, Book Reading 98220-3333
22, MIDC,
Mumbai,MH, INDIA.

M.M. Kale 2/1/71 Food, Drinks, Lifestyle 98220-6823
6/21,Silver Estate,
A'bad,MH, INDIA.

R.K. Joshi 9/10/70 Colletion of Old coins 98220-6877
Flat No.9, Pushpa Towers,
Pune,MH, INDIA.

N.K. Kulkarni 1/2/74 Computer Games 98220-9888
Sector 20, Padmavti,
Pune,MH, INDIA.
-------------------------------------------------------------------------

http://www.cyberciti.biz/pdf/lsst/datafiles/friends [7/29/2002 7:08:18 PM]

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