OS X seems to depend on how it's called.

$ perl -le 'print $^X'
perl
$ /usr/bin/perl -le 'print $^X'
/usr/bin/perl
$ perl -v

This is perl, v5.8.6 built for darwin-thread-multi-2level
...
[download]

Update: Unless of course you meant you need this specifically from people running 5.9.4 (which wasn't clear) . . .