What shell command to perform arithmetic with decimal values? 1

[pho01]

I'm trying to calculate a tablespace free percent from a shell script.
Percent Free=Total Free/Total_Availble *100

p_free=`expr $total_free / $total_max_bytes`

This always returns 0, which I can't do further calculation.
per_free=`expr $p_free \* 100`

What command should I use instead? thanks

 

[jxmac18]

bc offers a good degree of control:

echo "scale=2; $p_free \* 100" | bc -l

scale=2 to set the number of decimal places.

 

[pho01]

The first one is the one that I have trouble with. I changed that to the following:

p_free=`scale=2; expr $total_free / $total_max_bytes`

p_free=`scale=2; expr $total_free / $total_max_bytes | bc -l`

they all return 0

What did I do wrong?

thanks,

 

[tdatgod]

Hi,
I always just add some zeros the the equation.....

per_free=`expr ${total_free}00 / $total_max_bytes`

Granted this TRUNCATED the percent to the lower whole number.

I think the note above is a neat way to do this using your variables.

echo "scale=2 ; $total_free / $total_max_bytes * 100" | bc -l

 

[tdatgod]

BC stands for Binary calculator.

you use it instead of EXPR. But it accepts input from STDIN no the command line so you have to TRICK it into accepting your input from the command line.

That is where the ECHO comes in.

change.

p_free=`scale=2; expr $total_free / $total_max_bytes | bc -l`

to

p_free=`echo "scale=2; $total_free / $total_max_bytes * 100" | bc -l`

 

[pho01]

thank you. it worked great.

 

[Ygor]

Alternatively...

((p_free=100*total_free/total_max_bytes))