Arrays

08. ARRAYS

(positional parameters) The Bourne shell does support an array, but a word list can be created by using positional parameters. A list of words follows the built-in set command, and the words are accessed by position. Up to nine positions are allowed.The built-in shift command shifts off the first word on the left-hand side of the list. The individual words are accessed by position values starting at 1.

EXAMPLE

set word1 word2 word3

echo $1 $2 $3                                                Displays word1, word2, and word3

set apples peaches plums

shiftShifts off apples

echo $1                                                        Displays first element of the list

echo $2                                                        Displays second element of the list

echo $*                                                        Displays all elements of the list

 

 

Command substitution To assign the output of a Linux command to a variable, or use the output of a command in a string, backquotes are used.

 

EXAMPLE

variable_name=`command` 

echo $variable_name

now=`date`

echo $now

echo "Today is `date`"

9. FILE TESTING

The Bourne shell uses the test command to evaluate conditional expressions and has a built-in set of options for testing attributes of files, such as whether it is a directory, a plain file (not a directory), a readable file, and so forth.

EXAMPLE

-d File is a directory

-f File exists and is not a directory

–r Current user can read the file

–s File is of nonzero size

–w Current user can write to the file

#!/bin/sh

1 if [ –f file ]

then

echo file exists

fi

2 if [ –d file ]

then

echo file is a directory

fi

3 if [ -s file ]

then

echo file is not of zero length

fi

4 if [ -r file -a -w file ]

then

echo file is readable and writable

fi

10. EXECUTION OF SHELL SCRIPT :

1.By using change mode command

2.$chmod u + x sum.sh

3.$ sum.sh

or

$ sh sum.sh

 

 

VIVA-VOCE QUESTIONS

 

I) Number System Convertion.

 

   a) Convert hexadecimal to decimal.

 #bc

ibase=16

105

261

      b) convert decimal to binary.

#bc

obase =2

75

1110101

   c) convert decimal to hexadecimal

#bc

obase=16

203

010109

 

 

II) Display date with day-month-year.

Display 28-06-16 in the same format it is

echo" 28-06-16"

 

III) Create directory  as given.

                                                            A 

 


                           B                     C                        D

 

 


                                                          E                     F

      a) Create the file a and b in directory B.

      b) Copy the file a to b in directory E.

Step:

$mkdir  A

$A]mkdir B

$B]mkdir C

$C]mkdir D

$cd D

$mkdir E

$mkdir F

 

Enter B

Create a file a

Copy a to b

Answer:

cd B

cat> a

cat>b

cp a b

 

 


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