SOLVED

start of script

!/bin/bash

read expression result=expression" | bc -l) rounded_res=result") echo $rounded_res

read expr

result=expr" | bc -l)

printf "%.3f\n" "$result"

read input printf "%.3f\n" echo "$input" | bc -l

this works totally fine

result=$(echo "$expression" | bc -l)
printf "%.3f\n" "$result"

It will work, just a little trick

read expression

result=expression" | bc -l)

if [ result fi