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?

Carmencita

Sorry, mea culpa, mea maxima! – Polymeric

for maths operations, try to use bc or awk , not bash or expr – Arietta

Answer 1

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

Antihelix

It might help if you posted the actual command line you used. (I'm guessing you used more zeroes than I did.) I executed the commands above before I posted, and got the results given. Please try those first. – Antihelix

Huh, odd, I don't remember putting spaces in there originally. Anyhow, try removing your spaces and repeat. I edited my post to remove the problematic whitespace. – Antihelix

The question was to deal with floating point number; bash "let" returns integer – Triserial

Yes, HidekiAI, that's why I say to "imagine the decimal place where it belongs". The returned result 66666 represents an actual value of 66666 * 10^-3. – Antihelix

Answer 2

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

Veldaveleda

but i want to do this in script, the full line is : $ach_gs / $ach_gs_max * 100 – Carmencita

@maxorq: You might note that in all examples others have given, the multiplication is done first. This is a scientific computing thing -- since we know there are more digits available to the left of the decimal place than to the right, multiplication goes first to minimize loss of precision due to rounding. – Antihelix

Answer 3

just do it in awk

# awk 'BEGIN{print 20 / 30 * 100}'
66.6667

save it to variable

# result=$(awk 'BEGIN{print 20 / 30 * 100}')
# echo $result
66.6667

Arietta

This answer is very awkward. – Oblast

Good answer. There's a bigger change a system has awk than bc. – Pascha

Answer 4

I generally use perl:

perl -e 'print 10 / 3'

Edomite

it must be a very basic perl issue, but this command only displays a blank line on my system. perl -e 'print "hello world"' does not work either. But perl -e 'print "hello world\n"' does work as expected. – Whop

I'm afraid I can't help. All I can suggest is to add , "\n" to the end of the expression: perl -e 'print 10 / 3, "\n"' – Edomite

Thanks, this workaround works. (and your command works 'as-is' on another linux environment) – Whop

For the Pythonistas among us: python -c "print 10.0/3.0" – Changeful

Answer 5

> echo "20 / 30 * 100" | bc -l
66.66666666666666666600

This is a simplification of the answer by paxdiablo. The -l sets the scale (number of digits after the decimal) to 20. It also loads a math library with trig functions and other things.

Zachariahzacharias

Answer 6

Another obvious option:

python -c "print(20 / 30 * 100)"

assuming you are using Python 3. Otherwise, use python3.

Hexad

Answer 7

expr doesn;t support float,
You can make a simple c calculator and just use,

./mycal 22 / 7.0

Handgun