expr

Hi guys,

I've got a problem right here, but I know you can help me. ;-)
I want to devide two numbers using 'expr' command line tool.
But I can't devide numbers with commas, e.g. 10 / 2,5. 

This is how I wanted it to work:
  `expr 10 / 2,5`

The script says "non-numeric argument".

Then I tried:
  `expr 10 / 2.5'

The answer of the script is the same as above.
Of course, I'm not gonna use it as above. I wanted it to work with variables.

Because I wanted to make a script that converts physical stuff, I need to work 
with commas. Do you have any solution for me?

Thank you!

'Prof. Fosz' aka Fabian Foerster