59940188 Shell Scripting

7/28/2019 59940188 Shell Scripting

1/16

SHELL SCRIPT

By

N.Ravikumar


2/16

What is a Shell?

A shell is an environment in which we can run our commands,programs, and shell scripts.

The shell is often referred to as the UNIX system's commandinterpreter.

echo $0 command will return the type of the shell.

Interactive mode Shell receives input from user and executes it.


3/16

Jobs ofa Shell

Command Interpreter

Variable creation

I/O redirection(>,>>,


4/16

Shell Script

Shell script is a list ofcommands stored in a file that getsexecuted without any user intervention (i.e., Non-Interactive).

A shell program runs in 'interpretive'mode. Shell scripts runslower(but powerful) than those written in High level Language.

Non-Interactive Mode

Commonly used shell script naming convention:

filename.sh


5/16

Variables

A scalar variable holds only one value at a time.

The shell enables you to create, assign, and delete

variables.

Variables are defined as follows:variablename =value

e.gclass=10mx

To access the variableecho $class


6/16

Cont..

An environment variable is a variable that is available to anyprogram that is started by the shell.

A local variable is a variable that is present within the currentinstance of the shell. It is not available to programs that arestarted by the shell.

A shell variable is a special variable that is set by the shell andis required by the shell in order to function correctly.


7/16

Naming Convention

The name of a variable can contain only letters ( a to z orA to Z), numbers ( 0 to 9) or the underscore character ( _).

Variable's name can start with alphabets or an

underscore.

e.gValid :

class

_classInvalid:

1classclass@


8/16


9/16


10/16

Arrays

Set of variables.

Syntax:variablename[index]=value

e.g mark[0]=50mark[10]=100

Note: In the above the shelldoes not create blankarraybunch spacesbetween 0and 10.

Array index should be integer only. Accessing the values:

${name[index]}


11/16

Input/Output

Output(To the screen)- echo (\n,\t,\c,\b)

- printf (C-Language)

Input

- read (shell built-in command)

- To know whether read is a shell built-in command or not interminal type type read


12/16


13/16

Parameter Passing

Ability to specify arguments from commandline during theexecution of a shell script is called as parameter passing.

Within our script we can use parameter marker prefixed with

$sign and access the parameter.

e.g#!/bin/shecho "Hello $1"

>>./hello.sh WorldHello world


14/16

Cont..

$#To count the Total number of positional parameters.

$*To list out all the parameters.

#!/bin/shecho "Total Parameters : $#"printf "List of Parameters : \n $* \n"


15/16

References

Unix Concepts and Applications,Fourth Edition Sumitabha Das.

Sams Teach YourselfShell Programmin in 24 Hours -Sriranga Veeraraghavan.

http://steve-parker.org/sh/sh.shtml


16/16

THANK YOU

59940188 Shell Scripting

Documents

Transcript of 59940188 Shell Scripting