Conditional Structures in Shell Scripting - III

After if..else  and if..elfi..else we move to looping structures. Looping is supported in the form of for and while. Again they work semantically the same but syntactically different.

for Loop

Syntax

In bash shell there are two syntaxes.

1. for variable in list

   do 

     statement1 is executed till the list exhausts

   done

2. traditional for

 for (( variable_init ; condition ; variable_increment/decrement ))

   do

              statement1 is executed 

      till the condition returns false 

      done

Example:

	for i in 1 2 3 4 5
	do
	echo "Testing $i times"
	done

view raw fortest.sh hosted with ❤ by GitHub

Same program with second syntax

	#Here the spaces are for formatting purposes only.for is not sensitive to spaces
	for (( i=0 ; i<=5 ; i++ ))
	do
	echo "Testing $i times"
	done

view raw fortest2.sh hosted with ❤ by GitHub

while Loop
Nothing new about it. Just loops through the series of statements until the condition is true.
Syntax:
          #sensitive to white spaces
          while [ condition ]
          do
              statement1
              statement2
           done

	echo "Enter the number"
	read x
	#initialize looping variable
	i=0
	#check if i is less than 10
	while [ $i -le 10 ]
	do
	#print the value of x * i
	echo " $x * $i = $(( $x * $i ))"
	#increment i by 1
	i=$(( $i + 1 ))
	done

view raw whiletest.sh hosted with ❤ by GitHub

case Statement
case in bash scripting is very similar to switch case semantically . It save the trouble for writing a multilevel elif statements.

Syntax:

case $variable in
case1)  statement1;;
case2)  statement2;;
..
..
caseN) statementN;;
esac

	echo "Enter the number"
	read x
	case $x in
	1) echo "You entered one";;
	2) echo "You entered two";;
	3) echo "You entered three";;
	4) echo "You entered four";;
	5) echo "You entered five";;
	*) echo "Sorry not listed";;
	esac

view raw case.sh hosted with ❤ by GitHub