Solved

Bash Calulation

Posted on 2011-09-07
5
294 Views
Last Modified: 2012-05-12
HI,

I have a bash script and need to do a calculation and return an integer.
The issue I have is expr and bc don't deal with decimal exponents.

This is the excel equation I am trying to get working in bash.
ANSWER=INT($START*$CPU^0.422)

Does anyone know how to do this in bash and just return the rounded down value?
All decimal answers should be rounded down.

Thanks
Fixitben
0
Comment
Question by:fixitben
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
5 Comments
 
LVL 68

Expert Comment

by:woolmilkporc
ID: 36498629
echo $START $CPU | awk '{printf "%d", $1*$2^0.422}'

or, to use the variables inside awk and to avoid "echo"

1)
awk 'BEGIN {printf "%d", '$START'*'$CPU'^0.422}'

2)

awk -v S=$START -v C=$CPU 'BEGIN {printf "%d", S*C^0.42}'

wmp
0
 
LVL 68

Accepted Solution

by:
woolmilkporc earned 500 total points
ID: 36498637
The full statement

ANSWER=$(awk -v S=$START -v C=$CPU 'BEGIN {printf "%d", S*C^0.42}')
0
 
LVL 7

Author Closing Comment

by:fixitben
ID: 36498689
That worked great. Thanks
0
 
LVL 20

Expert Comment

by:edster9999
ID: 36498747
bc is a command that does just that.  If you do not specify the 'scale' to give it the number of decimal point places to use then it assumes no places and rounds down to the nearest integer.

Now the next step.  You can't do 'to the power of' in bc with a real number.  The value to the right has to be an integer.  Its just not going to handle that.

You'll need to convert it first.  Get your maths text book out and look up :
x^y = e^(y*log(x))
This is an alternative way of working out x^y and can  be handled by bc.
I've never done this part so you'll have to play round with it.
0
 
LVL 38

Expert Comment

by:Gerwin Jansen, EE MVE
ID: 36498948
With bc your answer would have been:

START=1.5
CPU=2
echo "e(0.477*l(${START}*${CPU}))" | bc -l
1.68883351312073475842

Open in new window


and rounded:

START=1.5
CPU=2
echo "e(0.477*l(${START}*${CPU}))" | bc -l | xargs printf "%1.0f\n"
2

Open in new window

0

Featured Post

Optimize your web performance

What's in the eBook?
- Full list of reasons for poor performance
- Ultimate measures to speed things up
- Primary web monitoring types
- KPIs you should be monitoring in order to increase your ROI

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

The purpose of this article is to demonstrate how we can use conditional statements using Python.
Utilizing an array to gracefully append to a list of EmailAddresses
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
How to Install VMware Tools in Red Hat Enterprise Linux 6.4 (RHEL 6.4) Step-by-Step Tutorial
Suggested Courses

636 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question