Shell Programming and Scripting

There may be a way, but it's a little screwy.

You could have a dummy header that reserves enough space for the real header. For example, it might say:

line count = xxxxxxx

Then you append your detail records and compute the real header. Finally you rewrite the first n bytes where n is the number of bytes in the header. To rewrite the first bytecount bytes use:

dd if=realheader bs=1 count=$bytecount conv=notrunc of=outputfile

Hi, as Perderabo suggested, you may leave space at the beginning and end with strings like space_for_header and space_for_footer. You may at last use stream editor sed to replace those strings with your header and footer info. I am not sure about the time taken but you can sure use your time wisely if you use the sed command in a script and let it run in the background. Hope it helps. Cheers