While Loop in Shell Script Examples
WHILE LOOP IN SHELL SCRIPT
While Loop
- It is an example of looping statements or iteration statements
- It is used to execute the statements, if the condition is true otherwise it will skip the loop
- It is an alternative for normal for loop.
Syntax
while [ condition ]
do
true statement
done
Types of Styles
- Shell Style
- C Style
Shell Style
- Here, we have to use the default shell style of syntax for writing the expression in the shell script.
C Style in Shell Script
- Here, we can write code for expression using c language style using double braces ((expression))
1. C STYLE BASED FACTORIAL CODE
Source Code
echo "--------------------------"
echo -e "\t Factorial Program"
echo "--------------------------"
echo "Enter a Number: "
read n
# define the variable
f=1
i=1
# define the while loop
while ((i<=n))
do
f=$((f*i))
((i++))
done
echo "Fact is: $f"
Output
2. SHELL STYLE BASED FACTORIAL CODE
Source Code
echo "--------------------------"
echo -e "\t Factorial Program"
echo "--------------------------"
echo "Enter a Number: "
read n
# define the vairable
f=1
i=1
# define while loop
while [ $i -le $n ]
do
f=`expr $f \* $i`
# increment the variable i
i=`expr $i + 1`
done
echo "The Factorial is: $f"
Note
- expr is a linux command which is used to perform basic arithmetic operations such as addition, subtraction, multiplication, division, modulus operation, etc,...
Output
IMPORTANT NOTE
- In shell script, the operators can't be used directly. Instead this can be used as keywords.
Operator Keywords
< -lt
<= -le
> -gt
>= -ge
== -eq
!= -ne
Infinite While loop
- It is an important to note that, the colon (:) operator or true keyword is used for creating an infinite loop
- The colon (:) operator is used instead of the operator symbols [ ]
3. EXAMPLE OF INIFINITE WHILE LOOP
Source Code
# define infinite while loop
# using colon : or true keyword
while true
do
echo "Hello World"
done
Output
Video Demo
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