On Wednesday, May 19, 2010 05:25:13 pm Ian Hobson wrote:
> On 19/05/2010 22:28, John Wu wrote:
> > Hi,
> > 
> > I want to write some content to an existing file and I want to new
> > content be the first line of the file. How to do that?
[snip]
> For file that will fit in RAM, load it, join with your first line, and
> save it all.
> 
> For larger files, you need to copy and rename.

Or for files whose contents you actually care about -- and many of those are 
small files. Think about what happens if you crash.

The typical method is to create a temporary file, insert the data, append the 
original file, then rename on top of the original file. Then the file is never 
in a corrupted state, even temporarily.