Fundamental of Linux &

Shell Programming

Presented By:-Rahul Hadahada.rahul@gmail.comMob:- 9001806370

18/12/13 OpenLab 2

RoadMap● Basic of shell programming

– Creation of shell program

– Using variables

– Pipes

– Performing math

– Handling user input

● Control Structure

– if-then-else

– Loops● For , while , until

● Creating Function

18/12/13 OpenLab 3

Basic of Shell Programming● Creating a shell program

– Specify the shell you are using in the first line– #!/bin/bash , #!/bin/ksh etc.– Ex: Shell program to print something

#!/bin/bash

echo “Welcome to the world of Shell Programming”

● Execution of program– Shell script never compile

– First change mode then execute – cs@poornima$ chmod 775 hello.sh or chmod u+x– cs@poornima$ ./hello.sh

18/12/13 OpenLab 4

Basic of Shell Programming

● Variables – we can access the value of variable using $ sign.– Types of variables

● Environment Variables – stores specific system information. ex. $HOME,$SHELL,$LANGUAGE, $HOSTNAME,$HOSTTYPE etc

● User Variables – stores our own values in a variable.● Ex:

#!/bin/bash | #!/bin/basha=5 | read aecho “Value of a=$a” | echo “Value of a=$a”

18/12/13 OpenLab 5

Basic of Shell Programming

● Backtick (` `)– It allow you to assign the output of a shell

command to a variable

– Ex:-

#!/bin/bash | #!/bin/bash | #!/bin/bash

date | d=`date` | echo date

| echo $d |

18/12/13 OpenLab 6

Basic of Shell Programming

● Pipes (|)– The output of one command is the input of the

other command.

– Command1 | command2

– grep poornima history.txt | wc -l

– Ex:

#!/bin/bash

a=`grep poornima history | wc -l`echo “Number of Lines Containing Pattern=$a”

18/12/13 OpenLab 7

Basic of Shell Programming

● Evaluating expression– Two ways to evaluate

● Using expr expression● Using $[ expression]● They work differently for multiplication ( * )

– #!/bin/bash | #!/bin/bash

b=5 | b=5

c=6 | c=6

a=`expr $b + $c` | a=$[$b +$c]

echo “Sum =$a” | echo “Sum=$a”

18/12/13 OpenLab 8

Basic of Shell Programming

● Exiting the script

Every command runs in the shell uses an exit status.

● Whose value vary from 0-255 ● Value stores on ? Or $?● Explicit exit status from script● cs@poornima$ echo $?

#!/bin/bash | #!/bin/bash | #!/bin/bash

hello | ls -ytr | ls -l

echo $? | echo $? | echo $?

18/12/13 OpenLab 9

Basic of Shell Programming

● Exit Status Codes– 0 -------- successful completion of the command

– 2 -------- misuse of shell commands

– 127 -------- command not found

– 130 -------- command terminated with Clt-C

example using program

18/12/13 OpenLab 10

Basic of Shell Programming

● Command line Parameters– It allow you to add data values to the command

line when you execute the script.

– Ex : cs@poornima$./sum.sh 23 56

– Shell uses special variable, called positional parameters.

– Represented from 0 – 9 i.e $0 - $9

#!/bin/bash

s=`expr $1 + $2`

echo “Sum=$s”

18/12/13 OpenLab 11

Basic of Shell Programming

● Some special variables releated to the command line parameters– $* , $@ , $#

#!/bin/bash | #!/bin/bash | #!/bin/bash

echo $# | echo $* | echo $@

– Shift command – it downgrades each parameter variable one position by default.

#!/bin/bash ./cli1.sh 3 4 5

shift

shift

echo $1

18/12/13 OpenLab 12

Control Structure

● If-then-else

testing of if condition using test & [ ]

Structure Example

if command | #!/bin/bash

then | if test $1 -gt $2

command | then

fi | echo “First CL is greater”

| else | echo “Second CL is greater”

18/12/13 OpenLab 13

Control Structure

● Test of numeric comparisons– n1 -gt n2 -- check if n1 is greater then n2

– n1 -eq n2 -- check if n1 is equal to n2

– n1 -lt n2 -- check if n1 is lesser then n2

– n1 -le n2 -- check if n1 is lesser or equal to n2

– n1 -ge n2 -- check if n1 is greater or equal to n2

– n1 -ne n2 -- check if n1 is not equal to n2

18/12/13 OpenLab 14

Control Structure

● Test of string comparisons– str1 = srt2 -- check if str1 is the same as str2

– str1 != str2 – check if str1 is not equal to str2

– str1 > str2 – check if str1 is greater then str2

– str1 < str2 – check is str1 is lesser then str2

– -n str1--check if str1 has a length greater then zero

– -z str1-- check if str1 has length is zero

Note : Must use escape (\) symbol while using > or <

18/12/13 OpenLab 15

Control Structure

● Test file comparisons– -d file -- check if file exist and is a directory

– -e file -- check if file exist

– -f file -- check if file exist and is a file

– -r file -- check if file exist and is readable

– -w file – check if file exist and is writable

– -x file – check if file exist and is executable

– and, few more

18/12/13 OpenLab 16

Control Structure

● Case Statementcase variable in | #!/bin/bash

pattern1 | pattern2) | read ch

command;; | case $ch in

pattern3) | a|e|i|o|u)

command ;; | echo “char. is vowel”

*) | ;;

command;; | *)

esac | echo ”char is not vowel”

| ;;

| esac

18/12/13 OpenLab 17

Control Structure

● Loops types in shell for , while , until

for var in listdo commanddone

● Different ways to represent for loop● Can redirect the output of for loop in file● For loop can take input from file

18/12/13 OpenLab 18

Control Structure

● While Loop

while test condition

do

commands

done

18/12/13 OpenLab 19

Control Structure

● Untile loop – works opposite way of while loop

until test commands

do

commands

done

18/12/13 OpenLab 20

Guess output ?

#!/bin/bash | #!/bin/bash

for var in” $*” | for var in “$@”

do | do

echo “Output=$var” | echo “Output=$var”

done |done

18/12/13 OpenLab 21

Creation of function

● Function – reuse of same shell code● In shell function is a mini-script● Creation of function by two ways

function name { | name () {

commands | commands

} | }

|

18/12/13 OpenLab 22

Creation of Function

● Passing parameters in function● Returing values from function can be three

types :-– By Default it return exit status of the last

executed command in the function

– We can also use return to modify the exit status as per our own requirement

– Using echo to return values

18/12/13 OpenLab 23

Creation of Function

● Passing array in function● Decleration of array

Ex:- myarray = (1 2 3 4 5)

access values of array -- ${myarray[$1]} index 1

${myarray[*]} all array

– Example FunArrVar.sh

18/12/13 OpenLab 24

Thank You