Problems with Linux programming looping examples

Problems with Linux programming looping examples

Just like 'C' Language looping Implementation,its same in the Shell Scripting with the While,If-Else,For.In every case a block is executed repeatedly until an exit condition is satisfied.

Syntax IF

if[ condition ] then

fi

For ex-

write a program for odd and even

echo"Enter the no"

read a

if[ a%2 -ge 0 ]

      echo "even"

else

      echo "odd"

fi

//As You can see a is a variable.in the if condition -ge stands for greater than or equal to.i.e.if a is equal to 0,its even otherwise odd.

Syntax while

while[ cond. ]

do

done

for ex.

echo "Enter the number"

read num

fact=1

while[ $num -gt 0 ]

do

let fact=fact*num;

let num=num-1

done

echo"Factorial value of num is"

echo $fact

//fact is a variable that has value i.num is user defined variable.this loop executes till num is greater than 1.suppose num is 5.it is greater than 0.

1 iteration-        fact=1*5

                            num-5-1

2 Iteration:-        num is 4 and greater than 0.so cond true.loop executes.fact=5

                             fact=5*4

                             num=4-1

3 Iteration:          num is now 3>0.cond true.loop executes.fact=20

                              fact=20*3

                              num=3-1

4 Iteration:          num is now 2>0.loop executes.fact=60

                             fact=60*2

                             num=2-1

5 Iteration:          num is now 1>0.loop executes.fact=120

                             fact=120*1

                             num=1-1

6 Iteration           num is now 0.is is not greater than 0.condition false.loop break.

                             Answer is 120.

Syntax Nested If-else

if[ condition ]

else if[ condition ]

else

fi

fi

for ex:

WAP to find the greatest no of three nos.

echo "Enter three nos"

read a,b,c

if[ a -gt b ]then

         if[ c -gt a ] then

                echo $ b

else if

                echo $c

fi

fi

fi

These are operators

-eq             equal to

-gt               greater than

-ge              greater than or equal to

-lt                 less than

-le                less than or equal to

-ne               not equal to