Ceil, Floor, Round off a devided number in Bash

In Bash, it only handle integers, so any decimal places are discarded when dividing integers.

There may be times when you want to round or round up the result of a division, so, I will introduce how to round, round up, or round down for decimal places.

1. Floor

If you discard the decimal part of the division operation, it will be calculated as follows.

• 2 / 2 = 1
• 5 / 2 = 2
• 5 / 3 = 1

Basically, since the shell discards the fractional part of a real number, you can divide integers as follows in Bash.

#!/bin/bash

a=$(( 2 / 2 ))
b=$(( 5 / 2 ))
c=$(( 5 / 3 ))

echo "a=${a}"
echo "b=${b}"
echo "c=${c}"

Output:

$ bash example.sh
a=1
b=2
c=1

2. Ceil

If you round up the decimal part of a division operation, the calculation will be as follows.

• 2 / 2 = 1
• 5 / 2 = 3
• 5 / 3 = 2

To round up the division result of A and B in the shell, you can use a mathematical trick to calculate A / B = (A + B - 1) / B.

In this example, I implemented a function ceiling() to round up the devided number from 2 integers.

#!/bin/bash

ceiling() {
  result=$(( ($1 + $2 - 1) / $2 ))
  echo $result
}

a=$(ceiling 2 2)
b=$(ceiling 5 2)
c=$(ceiling 5 3)

echo "a=${a}"
echo "b=${b}"
echo "c=${c}"

Output:

$ bash example.sh
a=1
b=3
c=2

3. Round off

If you round off the decimal part of a division operation, it will be calculated as follows.

• 2 / 2 = 1
• 5 / 2 = 3
• 4 / 3 = 1

To round the result of the division of A and B in the shell, use a mathematical trick to calculate A / B = (A + (B / 2)) / B.

In this example, I implemented a function roundOff() to round off the devided number from 2 integers.

#!/bin/bash

roundOff() {
  result=$(( ($1 + ($2 / 2)) / $2 ))
  echo $result
}

a=$(roundOff 2 2)
b=$(roundOff 5 2)
c=$(roundOff 4 3)

echo "a=${a}"
echo "b=${b}"
echo "c=${c}"

Output:

$ bash example.sh
a=1
b=3
c=1