Shell script to find whether number is prime or not

7 posts · originally from https://geek.digit.in/community/threads/shell-script-to-find-whether-number-is-prime-or-not.80714/

Okay,

So we've been told to write this shell script to find whether a number taken from user is prime or not.

I know the log, just haven't been able to implement it.

Can anyone help ?

Thanks

DARK LORD said:
Okay,

So we've been told to write this shell script to find whether a number taken from user is prime or not.

I know the log, just haven't been able to implement it.

Can anyone help ?

Thanks

tried dividing it by all integer numbers till half of itself, and piping the resultant numbers to a log file, and checking the log file for number of lines where the content is just <0> ? If the number is 2, its a prime number.

DARK LORD said:
Okay,

So we've been told to write this shell script to find whether a number taken from user is prime or not.

I know the log, just haven't been able to implement it.

Can anyone help ?

Thanks

Where r u getting the problem? Show ur script!

I am able to get it after reading ABS and BGB, but for one problem. 1 is identified as prime. What would be the best method to avoid this?
I can certainly give a simple if statement to check if input is 1, if it is then it will directly print not prime.
Any better way?

- count = 0
- for i = 1 to number,
if number % i = 0
count=count+1
- if count <=2, then print => prime

So for 1, count will be 1 and for every other prime it will be 2.

OK, converted from one of my earlier c program

btw, prime checking can be done upto square root, which will require a little more work.

Code:

#!/bin/sh
 
i=2
rem=1
 
echo -e "Enter a number: \c"
read num
 
if [ $num -lt 2 ]; then
 echo -e "$num is not prime\n"
 exit 0
fi 
 
while [ $i -le `expr $num / 2` -a $rem -ne 0 ]; do
 rem=`expr $num % $i`
 i=`expr $i + 1`
done
 
if [ $rem -ne 0 ]; then
 echo -e "$num is prime\n"
else
 echo -e "$num is not prime\n"
fi

Ya the running time wud be less then.