[SOLVED] Arithmetic operation in bash script, multiply by decimal number, how?

postcd · 06-27-2021, 08:25 AM

GNU bash, version 5.1.8(1)

How can i please do this in a bash script, i want to multiply certain number by decimal number 1.5

Non working attempts:

1)

Code:

result=$(( $number * 1.5 |bc -l ))
                    ^---------------^ SC2004: $/${} is unnecessary on arithmetic variables.
                                        ^-^ SC2079: (( )) doesn't support decimals. Use bc or awk.
                                             ^-- SC2154: bc is referenced but not assigned (for output from commands, use "$(bc ...)" ).
                                                 ^-- SC2154: l is referenced but not assigned.

Code:

2)
```
result=$(( $number * 1,5 ))
                    ^---------------^ SC2004: $/${} is unnecessary on arithmetic variables.

3)

Code:

#!/bin/bash
number=3456
result=$( echo "$number*1.5"|bc )
echo "$result"

output is decimal (5184.0) which i do not want, i want whole numbers only result

michaelk · 06-27-2021, 09:16 AM

bc does not have a built in integer function but with a scale of zero and dividing by 1 it does the same thing.
awk has a built in integer function.

Code:

#/bin/bash
number=3456

result=$(echo "$number*1.5/1" | bc )
echo "$result"

result=$( awk "BEGIN { print int($number*1.5)}" )
echo "$result"

TB0ne · 06-27-2021, 11:11 AM

Quote:

Originally Posted by postcd

GNU bash, version 5.1.8(1)
How can i please do this in a bash script, i want to multiply certain number by decimal number 1.5 Non working attempts:

Code:

result=$(( $number * 1.5 |bc -l ))
                    ^---------------^ SC2004: $/${} is unnecessary on arithmetic variables.
                                        ^-^ SC2079: (( )) doesn't support decimals. Use bc or awk.
                                             ^-- SC2154: bc is referenced but not assigned (for output from commands, use "$(bc ...)" ).
                                                 ^-- SC2154: l is referenced but not assigned.

Code:

2)
result=$(( $number * 1,5 ))
                    ^---------------^ SC2004: $/${} is unnecessary on arithmetic variables.

Code:

#!/bin/bash
number=3456
result=$( echo "$number*1.5"|bc )
echo "$result"

output is decimal (5184.0) which i do not want, i want whole numbers only result

As asked many times in the past, do basic research first. From the bash documentation (bold/emphasis theirs):

Quote:

Originally Posted by Bash Documentation

Section "6.5 Shell Arithmetic":

The shell allows arithmetic expressions to be evaluated, as one of the shell expansions or by using the (( compound command, the let builtin, or the -i option to the declare builtin.

Evaluation is done in fixed-width integers with no check for overflow, though division by 0 is trapped and flagged as an error

So you cannot using bash alone. Doing basic research for other ways to script this yields a lot of suggestions and examples. The simplest being:

Code:

#!/bin/bash
declare -i number=3456
result=$( echo "$number*1.5/1"|bc )
echo "$result"

You did not declare the initial variable as an integer, and doing a simple divide by one gives you what you're after. Along with many other possibilities, all using standard Linux utilities:

Code:

calc 3456*1.5
bc <<< "scale=0; (3456*1.5/1)"
perl -E "say 3456*1.5"
python -c "print(int(3456*1.5))
lua -e "print(string.format('%.0f',3456*1.5))"

...along with THOUSANDS of other ways to script/write this, with easily found examples.

shruggy · 06-27-2021, 01:15 PM

Well, the number 1.5 lends itself particularly well to doing this in Bash:

Code:

#!/bin/bash
number=3456
result=$((number*3/2))
echo "$result"

Or even

Code:

#!/bin/sh
number=3456
result=$((number+number/2))
echo $result

TB0ne · 06-27-2021, 01:39 PM

Quote:

Originally Posted by shruggy

Well, the number 1.5 lends itself particularly well to doing this in Bash:

Code:

#!/bin/bash
number=3456
result=$((number*3/2))
echo "$result"

Nice..always more than one way to do it.

teckk · 06-28-2021, 04:21 PM

Quote:

How can i please do this in a bash script, i want to multiply certain number by decimal number 1.5

Couple of quick examples:

#Multiply by 1.5

Code:

for n in {1..20}; do
    if (($n >= 1 && $n <= 6)); then
        echo -e "\nProducts for ("$n" * 1.5) is:"
        ans=$(("$n"00*3/2))
        echo "("$n" * 1.5) = $((${ans:0: 1}+0)).${ans: 1}"
    elif (($n >= 7 && $n <= 20)); then
        echo -e "\nProduct for ("$n" * 1.5) is:"
        ans=$(("$n"00*3/2))
        echo "("$n" * 1.5) = $((${ans:0: 2}+0)).${ans: 2}"
    fi
done

#Divide by 1.5

Code:

for n in {1..30}; do
    echo -e "\nQuotient for ("$n" / 1.5) is:"
    ans=$(("$n"00*2/3))
    echo "("$n" / 1.5) = $((${ans:0: -2}+0)).${ans: -2}"
done