.sh & getopts

[Aiza]

Matthew Seaman wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On 06/06/2010 05:57:37, Aiza wrote:
> 
> 
>> i) action="installworld"; flag_count=$((flag_count+1));;
> 
> Try it like this instead:
> 
> i) action="installworld"; flag_count=$(( $flag_count + 1 ));;
> 
> (Obviously, apply the equivalent change to the other lines)
> 
> 	Cheers,
> 
> 	Matthew
> 
Thank you that worked.

I have been looking for documentation on freebsd's sh shell programming.
Want to understand what is happening in that getopts I posted. Where can 
I find real explanations?