Get ceiling integer from number in linux (BASH)

Question

How would I do something like:

ceiling(N/500)

N representing a number.

But in a linux Bash script

Answer 1

Expanding a bit on Kalle's great answer, here's the algorithm nicely packed in a function:

ceildiv() {
    local num=$1
    local div=$2
    echo $(( (num + div - 1) / div ))
}

or as a one-liner:

ceildiv(){ echo $((($1+$2-1)/$2)); }

If you want to get fancy, you could use a more robust version validates input to check if they're numerical, also handles negative numbers:

ceildiv() {
    local num=${1:-0}
    local div=${2:-1}
    if ! ((div)); then
        return 1
    fi
    if ((num >= 0)); then
        echo $(( (num + div - 1) / div ))
    else
        echo $(( -(-num + div - 1) / div ))
    fi
}

This uses a "fake" ceil for negative numbers, to the highest absolute integer, ie, -10 / 3 = -4 and not -3 as it should, as -3 > -4. If you want a "true" ceil, use $(( num / div )) instead after the else

And then use it like:

$ ceildiv 10 3
4
$ ceildiv 501 500
2
$ ceildiv 0 3
0
$ ceildiv -10 1
-10
$ ceildiv -10 3
-4

Answer 2

Here's a solution using bc (which should be installed just about everywhere):

ceiling_divide() {
  ceiling_result=`echo "($1 + $2 - 1)/$2" | bc`
}

Here's another purely in bash:

# Call it with two numbers.
# It has no error checking.
# It places the result in a global since return() will sometimes truncate at 255.

# Short form from comments (thanks: Jonathan Leffler)
ceiling_divide() {
  ceiling_result=$((($1+$2-1)/$2))
}

# Long drawn out form.
ceiling_divide() {
  # Normal integer divide.
  ceiling_result=$(($1/$2))
  # If there is any remainder...
  if [ $(($1%$2)) -gt 0 ]; then
    # rount up to the next integer
    ceiling_result=$((ceiling_result + 1))
  fi
  # debugging
  # echo $ceiling_result
}

Answer 3

You can use awk

#!/bin/bash
number="$1"
divisor="$2"
ceiling() {
  awk -vnumber="$number" -vdiv="$divisor" '
  function ceiling(x){return x%1 ? int(x)+1 : x}
  BEGIN{ print ceiling(number/div) }'
}
ceiling

output

$ ./shell.sh 1.234 500
1

Or if there's a choice, you can use a better shell that does floating point, eg Zsh

integer ceiling_result
ceiling_divide() {
  ceiling_result=$(($1/$2))
  echo $((ceiling_result+1))
}

ceiling_divide 1.234 500

Answer 4

This is a simple solution using Awk:

If you want the ceil of ($a/$b) use

echo "$a $b" | awk '{print int( ($1/$2) + 1 )}'

and the floor use

echo "$a $b" | awk '{print int($1/$2)}'

Note that I just echo the dividend '$a' as the first field of the line to awk and the divisor '$b' as the second.

Answer 5

Mathematically, the function of ceiling can be define with floor, ceiling(x) = -floor(-x). And, floor is the default when converting a positive float to integer.

if [ $N -gt 0 ]; then expr 1 - $(expr $(expr 1 - $N) / 500); else expr $N / 500; fi

Ref. https://en.wikipedia.org/wiki/Floor_and_ceiling_functions

Answer 6

This function wont't add 1, if the division returns a non-floating number.

function ceiling {
    DIVIDEND=${1}
    DIVISOR=${2}
    if [ $(( DIVIDEND % DIVISOR )) -gt 0 ]; then
            RESULT=$(( ( ( $DIVIDEND - ( $DIVIDEND % $DIVISOR ) ) / $DIVISOR ) + 1 ))
    else
            RESULT=$(( $DIVIDEND / $DIVISOR ))
    fi
    echo $RESULT
}

Use it like this:

echo $( ceiling 100 33 )
> 4