Rounding up float point numbers bash

To extend Tim's answer, you can write a shell helper function round ${FLOAT} ${PRECISION} for this:

#!/usr/bin/env bash

round() {
  printf "%.${2}f" "${1}"
}

PI=3.14159

round ${PI} 0
echo
round ${PI} 1
echo
round ${PI} 2
echo
round ${PI} 3
echo
round ${PI} 4
echo
round ${PI} 5
echo
round ${PI} 6
echo

# Outputs:
3
3.1
3.14
3.142
3.1416
3.14159
3.141590

# To store in a variable:
ROUND_PI=$(round ${PI} 3)
echo ${ROUND_PI}

# Outputs:
3.142

In case input contains a number, there is no need for an external command like bc. You can just use printf:

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

Edit: In case the input is a formula, you should however use bc as in one of the following commands:

printf "%.3f\n" $(bc -l <<< "$input")
printf "%.3f\n" $(echo "$input" | bc -l)