Expression as a string (shell scripting)

Question

I have an expression declared as a string and I want the output to be the result of the expression. I am trying to solve it using shell scripting. For example

expr="123+456" 

expecting output

579

Thanks in advance.

Answer 1

I would suggest using bc

> echo "123+456" | bc
579

Hard to say more without more details about what you are trying to do

See this SO for more details about doing this only using bash

Answer 2

If you're dealing only in integers, bash can do it:

(( foo=123+456 ))
echo $foo

returns: 579

Answer 3

You need the arithmetic expransion syntax:

$ expr="123+456"
$ answer=$(($expr))
$ echo $answer
579