Most languages have the concept of loops. If we want to perform a task repetitively with a little bit of change, the loop is the solution to write the logic. Different types of loops are used in this scripting language. The following examples demonstrate the loops with some examples.
for loop
There are two types of syntaxes of for loop. In the first example, the loop is iterated based on the value of i. The first part is an initialization, the second part is condition checking and the last part is increment or decrement.
#!/bin/bash
for (( i=1; i<=5; i++ ))
do
echo "$i"
done
echo $x
In the following example, the loop iterates over the elements starting from 0 to 5. In the first iteration, i will be assigned 0, in the next iteration i will be 1, and so on.
#!/bin/bash
for i in 0 1 2 3 4 5
do
echo "$i"
done
echo $x
nested for loop
Similar to the if-else block, for loop can also be nested as shown below.
#!/bin/bash
echo "Stars"
for (( i=1; i<=5; i++ ))
do
for (( j=1; j<=i; j++ ))
do
echo -n " *"
done
echo ""
done
while loop
Any one of for or while loops can be used to perform repetitive tasks. The syntax of the while loop is shown in the following example.
#!/bin/bash
i=5
while test $i != 0
do
echo "$i"
i=`expr $i - 1`
done
nested while loop
Similar to for loop nesting, a while loop can also be nested as shown below.
#!/bin/bash
x=0
while [ $x -lt 10 ] ;
do
y=$x
while [ $y -ge 0 ] ;
do
echo "$y \c"
y=`expr $y - 1`
done
x=`expr $x + 1`
echo $x
done
until loop
There is another loop, until, which can be used instead of the while loop. But the difference is that the loop will run until the condition is true, whereas the while loop runs until the condition is false.
#!/bin/bash
x=1;
until [ $x -ge 10 ]
do
echo $x
x=`expr $x + 1`
done
select loop
#!/bin/bash
break and continue statement
Script to find an average of numbers.
#!/bin/bash
#
avg=0
temp_total=0
number_of_args=$#
if [ $# -lt 2 ] ; then
echo -e "Opps! I need at least 2 command line args\n"
echo -e "Syntax: $0: number1 number2 ... numberN\n"
echo -e "Example:$0 5 4\n\t$0 56 66 34"
exit 1
fi
for i in $*
do
temp_total=`expr $temp_total + $i`
done
avg=`expr $temp_total / $number_of_args`
echo "Average is $avg"
The sum of digits of a number
#!/bin/bash
if [ $# -ne 1 ]
then
echo "Usage: $0 number"
echo " I will find the sum of all digits for given number"
echo " For eg. $0 123, I will print 6 as sum of all digit (1+2+3)"
exit 1
fi
n=$1
sum=0
sd=0
while [ $n -gt 0 ]
do
sd=`expr $n % 10`
sum=`expr $sum + $sd`
n=`expr $n / 10`
done
echo "Sum of digit for number is $sum"
Factorial of a Number using Shell Script
#!/bin/bash
n=0
on=0
fact=1
echo -n "Enter a number to find factorial: "
read n
on=$n
while [ $n -ge 1 ]
do
fact=`expr $fact \* $n`
n=`expr $n - 1`
done
echo "Factorial for $on is $fact"
Reverse a Number using Shell Script
#!/bin/bash
if [ $# -ne 1 ]
then
echo "Usage: $0 number"
echo " Reseverse a number"
echo " For eg. 1234, It will print 4321"
exit 1
fi
n=$1
rev=0
sd=0
while [ $n -gt 0 ]
do
sd=`expr $n % 10`
rev=`expr $rev \* 10 + $sd`
n=`expr $n / 10`
done
echo "Reverse number is $rev"
Program for Fibonacci Series
# Input for N
read N
# First Number of the Fibonacci Series
a=0
# Second Number of the Fibonacci Series
b=1
echo "The Fibonacci series is : "
for (( i=0; i<N; i++ ))
do
echo -n "$a "
fn=$((a + b))
a=$b
b=$fn
done
# End of for loop
Armstrong number within a range
#!/bin/bash
i=1
read n
while((i-le$n))
do
c=$i; d=$i; b=0; a=0
#checking each number
while ((c>0))
do
#separating each digit
a=$((c%10))
#finding cube of each digit and adding them
b=$((b + a*a*a))
c=$((c/10))
done
if ((b==d));
then
echo "$i"
fi
i=$((i+1))
done
Happy Exploring!
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