I was wondering what the best way would be to do the following:

I have a text file. The name of the text file is abc123.dat. What I would like to do, is open that file, and insert the name of the file (abc123 .. without the extension) as the first line of the file and then save the file. I know that I need to open the file, insert the data, and then save it but some code examples would be helpful. What should I use to insert the data into the file?

Thanks in advance for any suggestions.
Greg