Re: bug: :if-exists :append

Jean,
please keep the discussion on the list.

> * Jean Louis <[email protected]> [2017-02-14 04:22:16 +0300]:
>
>> > OK, if you happen to know how to get file descriptor by sys:: let me
>> > know. Or how to append to file which is chattr +a
>> 
>> (require "linux")
>> (defparameter *my-stream*
>>   (ext:make-stream (linux:open filename (logior linux::O_APPEND linux::O_RDONLY) 0)
>>                    :direction :append ...))
>
> I cannot require "linux" for some reason, using 2.49+ development
> version which is too hard to compile.

this the "bindings/glibc" module.
http://clisp.org/impnotes/modules.html#incmod-bind

>> > I have tried that with SBCL and it appended to the file
>> 
>> interesting - what does my lisp code below do in SBCL?
>> 
>> 
>> >> --8<---------------cut here---------------start------------->8---
>> >> (with-open-file (s "my-append-only-file" :direction :output :if-exists :append)
>> >>   (let ((pos (file-position s)))
>> >>     (write-string "foo" s)
>> >>     (file-position s (- pos 3))
>> >>     (write-string "bar" s)))
>> >> --8<---------------cut here---------------end--------------->8---
> debugger invoked on a TYPE-ERROR in thread
> #<THREAD "main thread" RUNNING {10028DE633}>:
>   The value
>     -3
>   is not of type
>     (OR UNSIGNED-BYTE (MEMBER NIL :END :START))

oops, my bad.

--8<---------------cut here---------------start------------->8---
(with-open-file (s "my-append-only-file" :direction :output :if-exists :append)
  (let ((pos (file-position s)))
    (print pos)
    (write-string "foo" s)
    (print (file-position s))
    (file-position s pos)
    (print (file-position s))
    (write-string "bar" s)
    (print (file-position s))))
--8<---------------cut here---------------end--------------->8---

this should work without errors - if it does not, please try `:direction :io`.
the question is: will this append

* "foobar" (as per `O_APPEND`) or
* "bar" (as per `:if-exists :append`)

we should be able to figure that out by examining the printed
file-positions.

Thanks.

-- 
Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.1504
http://steingoldpsychology.com http://www.childpsy.net http://mideasttruth.com
https://ffii.org http://www.memritv.org http://camera.org http://jij.org
"Sustainability" without "population growth control" is hypocrisy.

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, SlashDot.org! http://sdm.link/slashdot
_______________________________________________
clisp-list mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/clisp-list