safe way to add contents to a file ?

[Jean-Christophe Helary]

I'm struggling with what is the ideal "elispy" way of adding contents to a file 
at a given position.

What I want it:
- create some content
- put that content at a specific location in a file saved on disk
 (current use case: add an xml block to an RSS file)

I thought write-region would do the trick but there are 2 issues with it

1) if APPEND is a number, that's the position from which my contents will 
*overwrite* the rest of the file (I want to *insert* my contents)

2) there are weird things like the whole code where I call this function is 
actually copied to the target file buffer and I have no idea how to prevent 
that.

So, I thought of something a bit convoluted:

use a temporary buffer
insert the contents of the file there
find the point where I want to insert my contents
find the end of the file
copy that region to a different buffer
write my contents from the point I specified above
append the copied region to that
write all that to the original file

But I thought, it's not like such things don't happen all the time in emacs, so 
there must be a better workflow.

But the reference is incredibly cryptic regarding that and the Intro does not 
address any file i/o at all...



Jean-Christophe Helary
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http://mac4translators.blogspot.com @brandelune