Arithmetic operation from a file using cat

Question

I have written a arithmetic operation in a file, below is my input. I'm trying to assign the result into a variable by

c=`cat file`

c=`echo cat file`

But is not working, What's the correct way to do it?

cat file
$(($a+$b))

Code Snippet:

a=40.3
b=7.4
c='cat file`

`$($a + $b)` is not a shell arithmetic expression. `$(($a + $b))` (or better `$((a + b))`) would be though. — Etan Reisner, Nov 21 '14 at 20:16
And what you are looking for here is `eval` I think though I would strongly reconsider needing to use `eval`. — Etan Reisner, Nov 21 '14 at 20:17
Thanks @EtanReisner i Have used `$(($a + $b))`, updated the question. Also tried `$((a + b))`. — Marjer, Nov 21 '14 at 20:24

Karoly Horvath · Answer 1 · 2014-11-21T20:30:14.330

2

Can I assume that you've created weird artificial requirements? The file in its current form isn't usable...

If you had c=$(($a+$b)) in the file, you could simply source it:

. ./file
echo $c    # 47

You could also have a script that expects two arguments, echo $(($1+$2)), and you could use it like this:

c=$(./file $a $b)

edited Nov 21 '14 at 20:30

answered Nov 21 '14 at 20:24

Karoly Horvath

I Have a huge number of variables and it's difficult to pass the argumnent. But `. ./file` is rounding the values, updated the input with float values `echo $c` `#47` i want the result as 47.7 – Marjer Nov 21 '14 at 20:48
still prefer to pass them. that's how you can build bigger programs. none of the solutions rounding, *your* approach does. see: http://stackoverflow.com/questions/6348902/how-can-i-add-numbers-in-a-bash-script – Karoly Horvath Nov 21 '14 at 20:53

1 Answers1