What does   . "$1"   mean when it is the first line in a perl script?

If that's really absolutely all there is on the first line, it means the file containing the script has been corrupted; characters have been lost off of the beginning (at least!) of the file. (Update: Of course, this assumes the script is (or was) Perl to begin with. Others have suggested this code fragment is a piece of a shell script, and this seems much more likely to be the answer!)