[ILUG] file open, what contents?

[Donncha O Caoimh]

I have a feeling I know the answer to this already, "yes", but I'll ask
anyway.

If I have a file on a web server that's being served to clients and I
open it from within a PHP script (or any language that uses the system
fopen() command I suppose). I seek to a certain part of the file, write
to the file there (replacing text already there), and it may take
several seconds, then I close the file again.

Question is, while I'm replacing the text in the middle of that file,
will web users see the old file until I close() it at the end?

Otherwise I've got to go make offline copies of those files..

Donncha.