How to do exponentiation in Bash

I tried

开发者_如何学Cecho 10**2

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

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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

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Various ways:

Bash

echo $((10**2))

Awk

awk 'BEGIN{print 10^2}'  # POSIX standard
awk 'BEGIN{print 10**2}' # GNU awk extension

bc

echo '10 ^ 2' | bc

dc

dc -e '10 2 ^ p'

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Actually var=$((echo 2^100 | bc)) doesn't work - bash is trying to do math inside (()). But a command line sequence is there instead so it creates an error

var=$(echo 2^100 | bc) works as the value is the result of the command line executing inside ()