Shell Programming and Scripting

How do i write a code to convert watt to dBm and vice versa?
1o log(w) + 30 = dBm

Thanks!

One way...

Code:

$ cat calc
#! /usr/bin/ksh
bc -l |&
print -p scale=6
while read watt?"enter watt -->  "; do
        print -p "l($watt)/l(10)*10+30"
        read -p dbm
        echo "watt = $watt     dbm = $dbm"
done
echo
exit 0
$ ./calc
enter watt -->  .835
watt = .835     dbm = 29.216870
enter watt -->  1.002
watt = 1.002     dbm = 30.008670
enter watt -->

Unfortunately, it does not work. I am basically looking for the log formula in UNIX. I have already tried a few such as:double log(double x), log(x) etc., but none seems to work.
Hope that helps.
Thanks for replying.

The "log(x)" function is available in (n)awk

Yes it does. It works perfectly. I tested it and I show the test results in my post. The first example .835 watts does indeed equal 29.216870 dbm. You can verify that on this page. That page uses milliwatts so look for 835 and see what value they calculated. If you still think my script is not correct, please provide an example of something it did wrong.

I am not saying your script is wrong. I just cannot get it to work. everytime I try to run it, i keep getting error messages saying i.e. watt not found. Maybe I am doing something wrong. Remember i am new to unix. i do not know my way around yet to make things work. Below is what I wrote:

[COLOR=Navy]echo "x is a positive integer"
echo "Enter x"
read x
expr double log(log(x))
assuming you enter 5 when asked to enter the value of x, the value in dB should be displayed on the screen.

My expr formula is not working. I am looking for a simple formula that works. Thanks for the help!

Put my script in a file called calc in your current directory. Do a "chmod u+x calc" to make the file executable. Then do "./calc" to run it.