Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
Solved

Bash Calulation

Posted on 2011-09-07
Medium Priority
295 Views
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.

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
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

LVL 68

Expert Comment

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

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

ID: 36498689
That worked great. Thanks
0

LVL 20

Expert Comment

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

ID: 36498948

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

and rounded:

``````START=1.5
CPU=2
echo "e(0.477*l(\${START}*\${CPU}))" | bc -l | xargs printf "%1.0f\n"
2
``````
0

Featured Post

Question has a verified solution.

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

Why Shell Scripting? Shell scripting is a powerful method of accessing UNIX systems and it is very flexible. Shell scripts are required when we want to execute a sequence of commands in Unix flavored operating systems. “Shell” is the command line i…