How to use expr on float?


Question

I know it's really stupid question, but I don't know how to do this in bash:

20 / 30 * 100

It should be 66.67 but expr is saying 0, because it doesn't support float. What command in Linux can replace expr and do this equalation?

1
24
10/24/2014 4:27:18 PM

Accepted Answer

As reported in the bash man page:

The shell allows arithmetic expressions to be evaluated, under certain circumstances...Evaluation is done in fixed-width integers with no check for overflow, though division by 0 is trapped and flagged as an error.

You can multiply by 100 earlier to get a better, partial result:

let j=20*100/30
echo $j

66

Or by a higher multiple of 10, and imagine the decimal place where it belongs:

let j=20*10000/30
echo $j

66666

6
8/10/2009 10:01:30 AM

bc will do this for you, but the order is important.

> echo "scale = 2; 20 * 100 / 30" | bc
66.66
> echo "scale = 2; 20 / 30 * 100" | bc
66.00

or, for your specific case:

> export ach_gs=2
> export ach_gs_max=3
> x=$(echo "scale = 2; $ach_gs * 100 / $ach_gs_max" | bc)
> echo $x
66.66

Whatever method you choose, this is ripe for inclusion as a function to make your life easier:

#!/bin/bash
function pct () {
    echo "scale = $3; $1 * 100 / $2" | bc
}

x=$(pct 2 3 2) ; echo $x # gives 66.66
x=$(pct 1 6 0) ; echo $x # gives 16

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