BASH Arithmetic operation not working

Question

The code below is meant to calculate the percentage completed when a file is getting dd.

percentDone=$(((varFileSize / backupSize) * 100)

I am able to debug the script running and the variables get assigned numbers. However as soon as the script runs this line percentDone remains at 0.

I have also tried this:

   percentDone=$((varFileSize / backupSize))            
   percentDone=$((percentDone * 100))

Any ideas please let me know as really struggling with this problem! Thank you!!

How about first multiply, then divide, as is usual with integers — Sami Kuhmonen
– Sami Kuhmonen, Commented Oct 19, 2016 at 18:34
BASH doesn't support floating point arithmetic. Use bc -l or awk — anubhava
– anubhava, Commented Oct 19, 2016 at 18:36
@SamiKuhmonen Division and Multiplication both have the same dominance. It also wouldn't stop the program from working either. Anubhava Thank you, I will look into this! — Jake S
– Jake S, Commented Oct 19, 2016 at 18:41
That's why the order matters. What is 1 / 100 * 100 and what is 1 * 100 / 100 when done with integers? That's the problem. — Sami Kuhmonen
– Sami Kuhmonen, Commented Oct 19, 2016 at 18:42
@anubhava: Have a look on this Pseudo floating point using pure bash — F. Hauri - Give Up GitHub
– F. Hauri - Give Up GitHub, Commented Oct 19, 2016 at 21:55

Alexey Guseynov · Accepted Answer · 2016-10-19 21:40:22Z

3

Since bash only supports integers you have to do the calculation other way around:

percentDone=$((varFileSize * 100 / backupSize))

Otherwise dividing anything less than backupSize with it will result in zero and multiplying it with anything won't help.

Alexey Guseynov

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answered Oct 19, 2016 at 18:45

Sami Kuhmonen

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