How to write the current buffer into some file?

How to write the current buffer into some file?

[Marcin Borkowski]

Hello list,

I'd like to do /some stuff/ on the current buffer.  /Some stuff/
includes creating a new file, similar to the current buffer, with some
modifications.  Say that I'm visiting file "./test.org"; I want /some
stuff/ to happen in "./test-output/test-output.org".  I can handle the
filename change (easy), creation of the directory (easy), but here's
where I'm (a bit) stuck: how to create a new buffer, do the
modifications, save it, and close/bury so that after my function
returns, the user sees the same buffer as before?  I can't just
write-file, since this will change the file I'm visiting.  Here's what
I've come up with:

I can clone the existing buffer (too bad that clone-buffer doesn't let
me do this if I'm visiting a file; why is that so?) by means of manually
creating it, copying the contents (by means of insert-buffer-substring,
for instance), doing my modifications, saving it, and (possibly)
burying.

Question 1: did I forget about something?  Should I wrap all this in
some (with-current-buffer ...)?  (I guess that if I call all this
interactively, and do not change the buffer of the selected window,
(with-current-buffer) is not necessary - but maybe (a) it's bad style
and/or (b) it can backfire when e.g. I decide to run my function
non-interactively (or maybe in some other circumstances)?

Question 2: What would happen if I didn't (bury-buffer) after all that
stuff?  Would it end up "just below" the current buffer in the buffer
list?

TIA,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Adam Mickiewicz University

Re: How to write the current buffer into some file?

[John Mastro]

Hi Marcin,

Marcin Borkowski <mbork@wmi.amu.edu.pl> wrote:
> Question 1: did I forget about something?  Should I wrap all this in
> some (with-current-buffer ...)?  (I guess that if I call all this
> interactively, and do not change the buffer of the selected window,
> (with-current-buffer) is not necessary - but maybe (a) it's bad style
> and/or (b) it can backfire when e.g. I decide to run my function
> non-interactively (or maybe in some other circumstances)?
>
> Question 2: What would happen if I didn't (bury-buffer) after all that
> stuff?  Would it end up "just below" the current buffer in the buffer

Yes, I always use `with-current-buffer' when working with a buffer,
because there are many functions that operate on "the current buffer" by
default.

If you use a combination of `with-current-buffer' and `write-region', no
call to `bury-buffer' will be necessary. Goofy example below:

    (with-current-buffer (clone-buffer)
      (insert "\nStuff happening!\n")
      (write-region (point-min) (point-max) "~/destination.txt"))

Hope that helps.

-- 
john

Re: How to write the current buffer into some file?

[Stefan Monnier]

> Question 2: What would happen if I didn't (bury-buffer) after all that
> stuff?

No: instead you should simply never display the auxiliary buffer.
E.g. don't use switch-to-buffer, find-file or any other
such abomination (they're nice *commands* to use interactively, but
they shouldn't be used within Elisp code).


        Stefan

Re: How to write the current buffer into some file?

[John Mastro]

John Mastro <john.b.mastro@gmail.com> wrote:
> If you use a combination of `with-current-buffer' and `write-region', no
> call to `bury-buffer' will be necessary. Goofy example below:
>
>     (with-current-buffer (clone-buffer)
>       (insert "\nStuff happening!\n")
>       (write-region (point-min) (point-max) "~/destination.txt"))

I didn't address the fact that `clone-buffer' won't work with a
file-visiting buffer, as you noted. Also, `with-temp-buffer' is probably
an even better fit than `with-current-buffer', if you don't need that
buffer to stick around when you're done.

Here's another example approach, hopefully more useful:

    (let ((buffer (current-buffer)))
      (with-temp-buffer
        (insert-buffer-substring buffer)
        (insert "\nStuff happening!\n")
        (write-region (point-min) (point-max) "~/destination.txt")))

--
john

RE: How to write the current buffer into some file?

[Drew Adams]

> I'd like to do /some stuff/ on the current buffer.  /Some stuff/
> includes creating a new file, similar to the current buffer, with
> some modifications.  Say that I'm visiting file "./test.org"; I want
> /some stuff/ to happen in "./test-output/test-output.org". 

You probably want `write-region' (or possibly `write-file', if you
want to visit the file).