Replacing the null character ^@ in a flat file

Question

I have a flat file generated from someone else's software. They insert the null character ^@ in certain positions of the file. I wish to replace them with something else like -9. How do I search and replace this character efficiently in terminal on Mac OS X?

Thanks.

There is another post addressing this question in linux.

Answer 1

(To maintain a SO tradition of proposing multiple answers with different tools for shell scripting questions):

With tr:

tr -d '\0'

Answer 2

With sed:

sed 's/\x0/-9/g' filename > newfile