Raise to the power in shell

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.

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.