CODEWITHSUNDEEP
bashshell
user1606946
user1606946

Reputation:

Division in script and floating-point

I would like to do the following operation in my script:

1 - ((m - 20) / 34)

I would like to assign the result of this operation to another variable. I want my script use floating point math. For example, for m = 34:

results = 1 - ((34 - 20) / 34) == 0.588

Upvotes: 50

Views: 90791

Answers (7)

mcepl
mcepl

Reputation: 2786

Just to note that many times you actually don’t need floating point arithmetic. For example, instead of

results = 1 - ((34 - 20) / 34) == 0.588

you can always write

results = 1000 - (((34 - 20) * 1000) / 34) == 588

which is the equivalent.

Upvotes: 0

Cyrus
Cyrus

Reputation: 88674

Teach bash e.g. integer division with floating point results:

#!/bin/bash

div ()  # Arguments: dividend and divisor
{
        if [ $2 -eq 0 ]; then echo division by 0; return 1; fi
        local p=12                            # precision
        local c=${c:-0}                       # precision counter
        local d=.                             # decimal separator
        local r=$(($1/$2)); echo -n $r        # result of division
        local m=$(($r*$2))
        [ $c -eq 0 ] && [ $m -ne $1 ] && echo -n $d
        [ $1 -eq $m ] || [ $c -eq $p ] && echo && return
        local e=$(($1-$m))
        c=$(($c+1))
        div $(($e*10)) $2
}  

    result=$(div 1080 633)                  # write to variable
    echo $result

    result=$(div 7 34)
    echo $result

    result=$(div 8 32)
    echo $result

    result=$(div 246891510 2)
    echo $result

    result=$(div 5000000 177)
    echo $result

Output:

    1.706161137440
    0.205882352941
    0.25
    123445755
    28248.587570621468

Upvotes: 20

wmeitzen
wmeitzen

Reputation: 110

I know this is an old thread, but this seemed like a fun project to tackle without using bc or invoking recursion. I'm sure it can be improved, but this maxed out my skill.

numerator=5
denominator=7 # - 0 -> returns "undef"
decimal_places=4 # - 0 -> same as echo $(( $numerator / $denominator ))
_result_sign=""
let _dp_exp=10**decimal_places
if [ $denominator -eq 0 ]; then _div_result_int_large=0; else let _div_result_int_large=$((numerator * _dp_exp / denominator)); fi
if [ $_div_result_int_large -lt 0 ]; then let _div_result_int_large=$(( _div_result_int_large * -1 )); _result_sign="-"; fi
let _div_result_int=$((_div_result_int_large / _dp_exp))
let _div_result_mant=$((_div_result_int_large - _div_result_int * _dp_exp))
let _dp_lzeros=$((decimal_places - ${#_div_result_mant}))
printf -v _div_result_mant_padded "%.${_dp_lzeros}d$_div_result_mant"
div_result="$_result_sign$_div_result_int"
if [ $decimal_places -gt 0 ]; then div_result="$_result_sign$_div_result_int.$_div_result_mant_padded"; fi
if [ $denominator -eq 0 ]; then div_result="undef"; fi
echo $div_result

Example output:

numerator=5
denominator=7
decimal_places=5
-> 0.71428

numerator=250
denominator=13
decimal_places=0
-> 19

numerator=-5
denominator=6
decimal_places=2
-> -0.83

numerator=3
denominator=0 # - uh-oh
decimal_places=2 # - can be anything, in this case
-> undef

Upvotes: 1

John Kugelman
John Kugelman

Reputation: 361739

You could use the bc calculator. It will do arbitrary precision math using decimals (not binary floating point) if you set increease scale from its default of 0:

$ m=34
$ bc <<< "scale = 10; 1 - (($m - 20) / 34)"
.5882352942

The -l option will load the standard math library and default the scale to 20:

$ bc -l <<< "1 - (($m - 20) / 34)"
.58823529411764705883

You can then use printf to format the output, if you so choose:

printf "%.3f\n" "$(bc -l ...)"

Upvotes: 61

siraj md
siraj md

Reputation: 101

echo $a/$b|bc -l

gives the result.

Example: 

read a b
echo $a/$b|bc -l

Enter a & b value as 10 3, you get 3.3333333333

If you want to store the value in another variable then use the code

read a b
c=`echo $a/$b|bc -l`
echo $c

It also gives the same result as above. Try it...

Upvotes: 10

minttux
minttux

Reputation: 435

Use this script open this file with favorite editor like:

$ sudo vim /usr/bin/div

Then paste this code:

#!/bin/bash
# Author: Danial Rikhteh Garan ([email protected])

if [[ -z "$1" ]] || [[ -z "$2" ]]; then
    echo "Please input two number"
    echo "for 100/50 use: div 10 50"
    exit 1;
fi

div=$(echo "$1/$2" | bc -l);
echo 0$div | sed 's/[0]*$//g'

Now chmod it to 755:

$ sudo chmod 755 /usr/bin/div

Now use it:

$ div 5 100
0.05

In your script you can use this:

var=$(div 5 100);
echo "$var"

Upvotes: -1

jordanm
jordanm

Reputation: 34964

Bash does not do floating point math. You can use awk or bc to handle this. Here is an awk example:

$ m=34; awk -v m=$m 'BEGIN { print 1 - ((m - 20) / 34) }'
0.588235

To assign the output to a variable:

var=$(awk -v m=$m 'BEGIN { print 1 - ((m - 20) / 34) }')

Upvotes: 27

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