Unix

© Copyright 2002 - 2006 HSBC Software Development India Pvt. Ltd. All rights reserved. 1

HSBC Global Technology

UNIX

-Kirtikumar Shinde

2© Copyright 2002 - 2006 HSBC Software Development India Pvt. Ltd. All rights reserved.

Topics

1. Introduction

2. Unix Filesystem

3. File Permissions

3. Advanced Commands

4. Shell

5. Shell Programming

6. AWK

7. My Learnings

8. Questions?


Introduction

Multi-user and Multitasking OS

Mostly Written in C at Bell Labs

Most of the servers are on Unix

Unix FlavorsSolaris

HP

AIX

Linux

Current DS Server – Which Unix?


Introduction

Architecture


Unix File System

An upside-down Tree/

etc bin export

home

user

ad s3910120

dev tmp

exam.txt work hobby.c proj1

date cal. . .

. . . . .

. .

. . .

. . . . . .. . .

. . .


File permissions

Changing permissionschmod g+w empl.txt

chmod 754 empl.txt

Changing ownershipchown gcdv_dev empl.txt

Changing groupchgrp develp empl.txt

reading

othersgroupowner

1 0 01 0 11 1 1-r -r - xr xw

executionwriting


Advanced Commands

SortSorts the contents of a file.

sort [-b f n r o t] [file name(s)]

Takes the contents of a file(s) and displays it in sorted order. Flags:

-b ignores blanks-f change all lower case letter to upper case before comparing-n numeric sort-r reverse usual order-o sends output of command to some file-t field delimiter

E.g. To sort the Emp.txt on 2nd field in reverse order $sort -t, -n -r +2 Emp.txt


Advanced Commands

grepSearches a file for pattern.

grep [-c i l v] <pattern> [file name(s)]

Takes the contents of a file(s) and displays it in sorted order.Flags:

-c displays count of matching lines.-i ignore the case while searching-l lists the names of files that matches pattern-v displays all lines that don’t contain the pattern

E.g. To display all lines in the ‘Emp.txt’ that match either the abc or xyz string: $grep "abc|xyz" Emp.txt


Advanced Commands

tar

Compression and decompression of files. tar -(x|c) [ v f r] <tarfile> [file name(s)]

Flags:-x extract from file.-c create new extract file.-v displays list files-f name of file follows-r append to old extract.

E.g. To compress file Emp.txt $tar -cvf Emp.tar Emp.txtTo decompress file Emp.tar $tar -xvf Emp.tar


Shell

Command interpreter that waits for commands, executes them and displays the results

Bourne shellDeveloped by Steve Bourne at AT&T

Korn shellDeveloped by David Korn at AT&T

C-shellDeveloped by Bill Joy for Berkeley Unix


Shell

Shell works as follows:Shell displays a prompt.

You type in a command.

You press the return key.

The shell interprets the commands typed and tries to find the correct programs to run.

The kernel runs the requested programs and returns the results to the shell.

The shell displays the command prompt again


Shell

Which Shell I am in ?finger –m myusername

Know your shell – Korn Shell – its featuresAliases – It allows shorthand for commands.Command history – Lets you recall previously entered commands.Command line editing – Allows us to edit commands vi style.Integrated programming features – It enables common programming tasks to be done cleanly & without creating extra processes.Support regular expressions.Advanced I/O features – Ability to carry out two way communication with concurrent processes.Increased speed of shell code execution.Has highly robust security features.


Shell system variablesPATH = Defines path shell must search in order to execute any command or file.

HOME = Indicates default working directory of the user.

PS1 = System prompt 1.

PS2 = System prompt 2, default value is “>”.

Shell


UNIX Shell Programming

Shell Script (Shell Procedure)A program written in shell programming language is known as a shell script or shell procedure.

Shell Programming LanguageThe shell programming language is a command language with a lot of features common to many computer programming languages, including the structured language constructs: sequence, selection, and iteration.

Command LanguagesCommand languages are interpreted languagesIt allows then use of Unix commands in scripts



Shell scripting keywords.Please Note : Script variables shouldn’t be same as keywords.

Looping constructs, to be discussed in coming slides.

set, unset

Readonly

Exit

Ulimit

Umask



Create - Simple Hello World shell script.

#!/bin/sh

echo "Hello World“

Make Files Executable$ chmod 777 HelloWorld.sh

Execute the shell scriptObserve the output ‘Hello World’ will be between two command prompts.$ HelloWorld.sh



AssignmentsValue assignments.String assignment – var=“Your Name”

Think if not within double quotes.

$echo $varthink if not $

Making variable readonly.a=50readonly a



echo and Escape CharactersDisplay strings as “printf” in C

The echo command recognizes escape characters. Escape characters all start with the backslash ( \ ), and you can use them as part of the echo command argument string.

E.g.$ echo “\nHello\n”



Passing parameters to a Shell scriptConsider Welcome.sh, & we are sending name as parameter to a Shell Script.

Welcome.sh Vikram

think If you want to send First name & Last name as one parameter.

In above case 0th parameter value considered will be script name.1st parameter value considered will be name, i.e.Vikram.

Accessing parameters in a Shell scriptParameter to a shell script starts from index 1. Its value is retrieved by using $1 & so on. … Think how you will access parameter beyond 9th parameter.



Shell Positional Variable$0 : command itself

$1 : first parameter

$n : nth parameter

$# : no. of parameters

$? : exit status of last command executed

$* : all parameters

$$ : process number of shell

$! : PID of last background process



if-then and if-then-elseThe if-then Construct

if [ condition ]

then

true-commands

fi

The if-then-else Construct

if [ condition ]

then

true-commands

else

false-command(s)

fi



if-then-elif

if [ condition1 ]

then

commands_1

elif [ condition2 ]

then

commands_2

else

commands_n

fi



test CommandThe test command is a built-in shell command that evaluates the expression given to it as an argument and return true if the expression is true, if otherwise, false.You can use square brackets ( [ ] ) instead of the word test.Example

if test $str1 = $str2 then

echo “Something”fi

if [$str1 = $str2] then




Logical Operators-a AND Operator-o OR Operator! NOT Operator

Numeric Test Operators-eq Is number1 equal to number2 ?-ne Is number1 not equal to number2 ?-gt Is number1 great than number2 ?-ge Is number1 great than or equal to number2 ?-lt Is number1 less than number2 ?-le Is number1 less than or equal to number2 ?

E.gif test $var –lt 10

thenecho “Something”

fi



String Test Operatorsstring1 = string2 Does string1 match string2?string1 != string2 Does string1 not match string2?-n string Does string contain characters?-z string Is string an empty string?

E.g.if test $str1 = $str2

thenecho “Something”

fi

Think if no space on both sides of an operator



File Test Operators-s file True if File size is greater than 0-f file True if File exists & not a directory-d file True if file exists & is a directory file. -r file True if file exists & you have read permission on it.-w file True if file exists & you have write permission on it.-x file True if file exists & you have execute permission on it.

E.gif [ –f $filename ]then


Think if no space on both sides of an option.



The expr CommandArithmetic Operators+ : Addition operator

- : Subtraction operator

/ : Division operator

* : Multiplication operator

% : Remainder operator

ExpressionsArithmetic expressiona=`expr $a + $b` … think if no space both the sides of + & space both the sides of =.

Floating point arithmetic expression a=`expr $a + $b | bc`String expressionpath=$path1”/”$path2



While Loop

while [ condition ]docommand(s)done

For Loop

for variable in list-of-valuedocommand(s)done


AWK

Introduction to awk.awk is a programming language designed to search for, match patterns, and perform actions on files. awk programs are generally quite small, and are interpreted.

awk scans input lines one after the other, searching each line to see if it matches a set of patterns or conditions specified in the awk program. For each pattern, an action is specified. The action is performed when the pattern matches that of the input line.

Sample awk command:awk ‘/pattern/’’{print $0}’ file1


My Learnings

When I will go for Shell scripting.Automating my regular tasks.

Customizing my work environment.

Task is pretty simple

When I will avoid Shell scripting.It needs interaction with multiple applications.

Problem is relatively complex involves more than one tool.

Lookups or finding data.


Questions ?


Thank You

Unix

Economy & Finance

shell korn shell

shell programming language

path shell

shell command interpreter

att cshell

att korn shell

results bourne shell

shell system variables