Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

Bash Calulation

Posted on 2011-09-07
5
Medium Priority
?
296 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 2000 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

Keep up with what's happening at Experts Exchange!

Sign up to receive Decoded, a new monthly digest with product updates, feature release info, continuing education opportunities, and more.

Question has a verified solution.

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

Google Drive is extremely cheap offsite storage, and it's even possible to get extra storage for free for two years.  You can use the free account 15GB, and if you have an Android device..when you install Google Drive for the first time it will give…
I have written articles previously comparing SARDU and YUMI.  I also included a couple of lines about Easy2boot (easy2boot.com).  I have now been using, and enjoying easy2boot as my sole multiboot utility for some years and realize that it deserves …
This video shows how to set up a shell script to accept a positional parameter when called, pass that to a SQL script, accept the output from the statement back and then manipulate it in the Shell.
This demo shows you how to set up the containerized NetScaler CPX with NetScaler Management and Analytics System in a non-routable Mesos/Marathon environment for use with Micro-Services applications.
Suggested Courses
Course of the Month11 days, 5 hours left to enroll

885 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