You could use sed like one poster suggested, or you could have those 3 lines saved as a file. Let's say you call this file svn_header.
Now all you have to do is -
cat svn_header source_file > source_file_with_header
mv source_file_with_header source_file
You have to do this "redirection dance" with sed anyway, and since you are always adding the lines at the very beginning,
you should be okay with just using cat.
If you decide to go with Perl, you can do an in-place edit.
HTH,
- Anand
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." -- Antoine de Saint-Exupery