Most Common UNIX Commands Part - IV

There might be a scenario where we need a same statement  be executed for some 'n' number of times in those cases we usually go for loop commands. We have used these in c,c++,java.The same can be used even in unix shell scripting too

Let's see about some loop commands which can be used in shell scripting. If,For,While,Until.

IF-   If  keyword followed by condition then set of statements that should be executed upon satisfying the condition and then if loop will be ended with fi keyword

syntax:

       if [expression/condition]

        then

        statements to be executed

        fi

eg:   

#!/bin/sh

a=10

b=20

if [ $a == $b ]

then

   echo "a is equal to b"

fi

 for if-else it will be as follows

#!/bin/sh

a=10

b=20

if [ $a == $b ]

then

   echo "a is equal to b"

else

  echo "a is not equal to b"

fi

For nested if else it should be represented in the following way

#!/bin/sh

a=10

b=20

if [ $a == $b ]

then

   echo "a is equal to b"

elif [ $a -gt $b ]

then

   echo "a is greater than b"

elif [ $a -lt $b ]

then

   echo "a is less than b"

else

   echo "None of the condition met"

fi

For : for each variable it will check for condition/values if it is satisfied then set of statements are executed

Syntax:

for var in condn1 condn2 ... condnN

do

   Statement(s) to be executed for every condn.

done

eg:

#!/bin/bash

for i in 1 2 3 4 5

do

   echo "Welcome $i times"

done

Output will be as follows

Welcome 1 times

Welcome 2 times

Welcome 3 times

Welcome 4 times

Welcome 5 times

We will see about more unix loop commands in the coming article

Hope this helps you in understanding unix loop commands