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Re: safe way to add contents to a file ?

From: Jean-Christophe Helary
Subject: Re: safe way to add contents to a file ?
Date: Fri, 20 Dec 2019 22:50:29 +0900

Ok, here is my attempt at this:

(setq myText "<item>bla</item>")
(setq myMarker "<!-- place new items before this comment -->")
(setq myFile "/path/to/test.xml")

(defun myInsert (myText myMarker myFile)
    (set-buffer (find-file-noselect myFile))
    (goto-char (point-min))
    (goto-char (- (search-forward myMarker) (length myMarker)))
    (insert myText)

(myInsert myText myMarker myFile)

I've used find-file-noselect and insert, as suggested.

Are there things I can do to make that code more idiomatic ? Is there anything 
I am seemingly not understanding ?

Thank you in advance.


> On Dec 18, 2019, at 9:36, Óscar Fuentes <> wrote:
> Jean-Christophe Helary <>
> writes:
>> 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-file-noselect takes care of creating the buffer and reading the
> contents of the file. Later you must get rid of the buffer.
>> find the point where I want to insert my contents
> use `insert' or `insert-buffer-substring'
>> 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...
> The sequence of operations above is actually quite simple (although not
> very efficient if the target file is large and your new content is near
> the end).

Jean-Christophe Helary
----------------------------------------------- @brandelune

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