Automatic Way to Tell if a FreeBSD system is 64 or 32-bit?

[Eitan Adler]

>        I have built a fairly decent Bourne shell script to run
> just after installing mfsbsd on a target system. It figures out
> the likely boot drive, formats it and then begins to build a
> FreeBSD system on it. The script could intelligently ask for the
> 64-bit or 32-bit trees if it could determine whether it was
> running on the i86 or 64-bit system.
>

Either sysctl -n hw.machine_arch or uname -m (which is POSIX compliant)