Lab 8

Shell Script

Reference: Linux Shell Scripting Tutorial v1.05r3A Beginner's handbook http://www.freeos.com/guides/lsst/index.html

myscript $0foo $1Bar $2

Special shell variables $0…$9

$# tells you how many parameter your script was given

Positional parameters or command line arguments

myscript foo bar

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... fi

test expression or [ expr ] - -True return zero(0)Is used to see if an expression is true - -False returns nonzero Syntax:

test expression OR [ expression ]

$ vi ispositive # Script to see whether argument is positive#if test $1 -gt 0thenecho "$1 number is positive"fi

Run it as follows:

$ chmod 755 ispositive $ ./ispositive 5

test expression or [ expr ]

For test statement with if commandFor [ expr ] statement

with if command

For test statement with if commandFor [ expr ]

statement with if command

Mathematical Operator in  Shell Script Meaning

Mathematical Operator in  Shell

Script Meaning

if [ 5 -eq 6 ] if test 5 -eq 6 is equal to -eq

if [ 5 -ne 6 ] if test 5 -ne 6 is not equal to -ne

if [ 5 -lt 6 ] if test 5 -lt 6 is less than -lt

if [ 5 -le 6 ] if test 5 -le 6 is less than or

equal to -le

if [ 5 -gt 6 ] if test 5 -gt 6 is greater than -gt

if [ 5 -ge 6 ] if test 5 -ge 6 is greater than or

equal to -ge

test expression or [ expr ]

String Comparisons

Meaning Operator           

string1 is equal to string2 string1 = string2

string1 is NOT equal to string2 string1 != string2

string1 is NOT NULL or not defined  string1

string1 is NOT NULL and does exist -n string1

string1 is NULL and does exist -z string1

test expression or [ expr ]

Logical Operators

Meaning Operator           

Logical NOT ! expression

Logical AND expression1  -a  expression2

Logical OR expression1  -o  expression2

if …else…fi If given condition is true then command1 is executed

otherwise command2 is executed.

Syntax:

if condition then

command1 else

if condition is not true then execute all commands up to fi fi

Exercise ( if..else with parameters)

if [ $# -eq 0 ]then echo " Enter one argument “ exit 1 else   echo " The first argument is $1 " fi

if …else…fi $ vi isnump_n

# Script to see whether argument is positive or negative

if [ $# -eq 0 ]thenecho "$0 : You must give/supply one integers"exit 1fi if test $1 -ge 0thenecho "$1 number is positive"elseecho "$1 number is negative"fi

$ chmod 755 isnump_n

$ ./isnump_n 5

if …else…fi Syntax:

if condition Then

if condition then

.....

.. do this

else .... .. do this

fi else

... ..... do this

fi

Nested if-else-fi $ vi nestedif

osch=0echo "1. Unix (Sun Os)"echo "2. Linux (Red Hat)"echo –n "Select your os choice [1 or 2]? "read oschif [ $osch -eq 1 ] ; then     echo "You Pick up Unix (Sun Os)"else        if [ $osch -eq 2 ] ; then             echo "You Pick up Linux (Red Hat)"       else             echo "error only 1 or 2"       fifi

$ chmod 755 nestedif

$ ./ nestedif

Multilevel if-then-elseSyntax:

if condition then

condition is zero (true - 0) execute all commands up to elif statement

elif condition1 then

condition1 is zero (true - 0) execute all commands up to elif statement

elif condition2 then

condition2 is zero (true - 0) execute all commands up to elif statement

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

$ vi elf

# 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

$ chmod 755 elf

$ ./ elf 8

$ ./ elf -3

$ ./ elf 0

$ ./ elf a

for Loop

$ vi testfor

for NUMBER in 1 2 3 4 5doecho "Welcome $NUMBER times"done

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

$ vi for2 LIMIT = 10for ((  i = 1 ;  i <= LIMIT;  i++  ))do  echo "Welcome $i times"done

for Loop$ vi nestedfor 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

while loop Syntax:

while [ condition ] do

command1 command2 command3 .. ....

done Write script to print numbers as 5,4,3,2,1, using while loop. The biggest number is supplied as command line argument.

i=$1while test $i != 0do echo –n "$i ," i=`expr $i - 1`doneecho " "

Exercise (1)

Write shell script using for loop to print the following patterns.

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

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