Question

I tried

echo 10**2

which prints 10**2. How to calculate the right result, 100?

Answer 1

You can use the let builtin:

let var=10**2   # sets var to 100.
echo $var       # prints 100

or arithmetic expansion:

var=$((10**2))  # sets var to 100.

Arithmetic expansion has the advantage of allowing you to do shell arithmetic and then just use the expression without storing it in a variable:

echo $((10**2)) # prints 100.

For large numbers you might want to use the exponentiation operator of the external command bc as:

bash:$ echo 2^100 | bc
1267650600228229401496703205376

If you want to store the above result in a variable you can use command substitution either via the $() syntax:

var=$(echo 2^100 | bc)

or the older backtick syntax:

var=`echo 2^100 | bc`

Note that command substitution is not the same as arithmetic expansion:

$(( )) # arithmetic expansion
$( )   # command substitution