Raise to the power in shell

Question

How do you raise m to the power of n? I've searched for this everywhere. What I found was that writing m**n should work, but it doesn't. I'm using #!/bin/sh.

Steamboat

because m**n is a bash feature that is not available in sh – Parnassian

Answer 1

I would try the calculator bc. See http://www.basicallytech.com/blog/index.php?/archives/23-command-line-calculations-using-bc.html for more details and examples.

eg.

$ echo '6^6' | bc

Gives 6 to the power 6.

Moynihan

Awesome! Used to do my own math functions in bash, created a lot of useless ugly code! Thanks! Didn't know about bc. – Jeffreys

if you can spare 40 more megabytes to install it, PARI/GP does the trick and can handle bigger numbers, is faster, and has richer computations. to answer the original question: echo 6^6 | gp -q – Accentuate

Downvoted why ? – Moynihan

Answer 2

Using $n**$m really works indeed. Maybe you don't use the correct syntax to evaluate a math expression. Here's how I get the result on Bash:

echo $(($n**$m))

or

echo $[$n**$m]

The square brackets here are not meant to be like the test evaluator in the if statement so you can you use them without spaces too. I personally prefer the former syntax with round brackets.

Muskogee

This question asked for a solution for shell which means POSIX shell. Your solution does not work in a POSIX compliant shell like dash but just happens to work in more featureful shells like bash or zsh. – Edora

This is the answer that I was looking for and that I would accept. Thank you @Muskogee – Farrington

Note that this is limited to integers only - Bash can't handle non-integer arithmetic. Also, echo $((n ** n)) will work as well - no need for $ to expand variables inside the arithmetic expression, (( ... )). – Abbe

Careful with this if you're dealing with large numbers. For example, $((2**100)) gives 0 on my machine. Using bc works with larger numbers. – Kallman

Yes, this is very nice, but while $((2**62)) is fine - $((2**63)) produces a negative number: presumably overflowing 64-bits. – Exoskeleton

Answer 3

using bc is an elegant solution. If you want to do this in bash:

$ n=7
$ m=5

$ for ((i=1, pow=n; i<m; i++)); do ((pow *= n)); done
$ echo $pow
16807

$ echo "$n^$m" | bc  # just to verify the answer
16807

Teens

In bash you can also use $((7**5)). – Pentaprism

well, then. that's even easier. – Teens

Answer 4

You might use dc. This

dc -e "2 3 ^ p"

yields

8

Pentaprism

this might interest ppl interested in dc unix.stackexchange.com/a/124524/30352 – Padilla

Answer 5

My system admin didn't install dc so adding to other correct answers, I bet you have not thought of this -

a=2
b=3
python -c "print ($a**$b)"
>> 8

works in bash/shell.

Lobate

Answer 6

#! /bin/bash
echo "Enter the number to be done"
n=2
read m
let P=( $n**$m )
echo "The answer is $p"

---

ANSWER

Enter the number to be done
3
The answer is 8 

Pushball