Re: exif --remove not idempotent, and a Debian man page bug

[David Wright <deblis@lionunicorn.co.uk>]

On Mon 26 Sep 2022 at 21:31:55 (+0200), Emanuel Berg wrote:
> Greg Wooledge wrote:
> 
> >> Look more, quote less ...
> >> 
> >>     <incal> for f in **/*.jpg; do exif --remove -o $f $f; done | grep
> >  'Wrote
> >>             file' | wc -l # 2277 (1st invocation)
> >>             
> >>     <incal> for f in **/*.jpg; do exif --remove -o $f $f; done | grep
> >  'Wrote
> >>             file' | wc -l # 2277 (2nd invocation)
> >
> > There is NO exif output in that message.
> 
> It's IPC, piped to wc. You want me to yank it here? Sure, just
> ask man ...
> 
> $ repeat 2 for f in **/*.jpg; do exif --remove -o $f $f; done 2>&1 | head -n 10
> <f --remove -o $f $f; done 2>&1 | head                                       -n 10
> Wrote file 'berlin.jpg'.
> Corrupt data
> The data provided does not follow the specification.
> ExifLoader: The data supplied does not seem to contain EXIF data.
> Wrote file 'bike/25-balls.jpg'.
> Wrote file 'bike/bike-swamp/adv/vasteras/adv-gear.jpg'.
> Wrote file 'bike/bike-swamp/moas-valve/moas-valves.jpg'.
> Wrote file 'bike/bike-swamp/moas-valve/valves-2.jpg'.
> Wrote file 'bike/bike-swamp/pigeon/front.jpg'.
> Wrote file 'bike/bike-swamp/pigeon/hermes.jpg'.
> Wrote file 'berlin.jpg'.
> Corrupt data
> The data provided does not follow the specification.
> ExifLoader: The data supplied does not seem to contain EXIF data.
> Wrote file 'bike/25-balls.jpg'.
> Wrote file 'bike/bike-swamp/adv/vasteras/adv-gear.jpg'.
> Wrote file 'bike/bike-swamp/moas-valve/moas-valves.jpg'.
> Wrote file 'bike/bike-swamp/moas-valve/valves-2.jpg'.
> Wrote file 'bike/bike-swamp/pigeon/front.jpg'.
> Wrote file 'bike/bike-swamp/pigeon/hermes.jpg'.

Well——yes—I thought most people were interested in the output of
$ exif foo.jpg   much more than whether there are 2277 lines from
$ exif --remove … …   being executed on some collection of files;
IOW what's being done to the EXIF in their images.

> > The only "output" there is from wc -l, and it's you typing
> > it as a comment after the shell command, not even showing
> > it properly.
> 
> Okay, is that in a RFC or somewhere in the POSIX specification?

What? exhorting users to paste their commands' stdout rather than
transcribing it into a comment?

> > The entire thread was a result of your assumption that exif
> > would NOT write the words "Wrote file" if the input file had
> > no exif tag in it. This turned out to be false. exif writes
> > those words every time.
> 
> IMO it shouldn't write anything if nothing happens and in
> particular it shouldn't take time, which it does. Every time.

I won't ask why you feel the need to keep running with --remove
over and over.

> OK, how should it be done? No computing the second time the
> metadata is removed?

Why oh why "second time"? It's not as if you're removing
individual tags in turn, and using the intermediate versions
of the images for some purpose. I just don't understand the
point of this exercise.

> You do the triangular dance with
> filenames, i.e. the tool can't do that? Is that what you mean?

Cheers,
David.