Solved

Bash Calulation

Posted on 2011-09-07
5
289 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
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 37

Expert Comment

by:Gerwin Jansen
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

What is SQL Server and how does it work?

The purpose of this paper is to provide you background on SQL Server. It’s your self-study guide for learning fundamentals. It includes both the history of SQL and its technical basics. Concepts and definitions will form the solid foundation of your future DBA expertise.

Question has a verified solution.

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

Suggested Solutions

It’s 2016. Password authentication should be dead — or at least close to dying. But, unfortunately, it has not traversed Quagga stage yet. Using password authentication is like laundering hotel guest linens with a washboard — it’s Passé.
Active Directory replication delay is the cause to many problems.  Here is a super easy script to force Active Directory replication to all sites with by using an elevated PowerShell command prompt, and a tool to verify your changes.
Learn how to find files with the shell using the find and locate commands. Use locate to find a needle in a haystack.: With locate, check if the file still exists.: Use find to get the actual location of the file.:
Connecting to an Amazon Linux EC2 Instance from Windows Using PuTTY.

914 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

Need Help in Real-Time?

Connect with top rated Experts

14 Experts available now in Live!

Get 1:1 Help Now