Raiders of the Lost Downboat

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Eliah Kagan

01:58

@Zanna The OP uses the same glob twice, one for input and once for output. If the command accepts a list of input files and a list of corresponding output files, and doesn't overwrite an output file before fully reading the corresponding input file, then it would work; I believe the shell should expand the same glob the same way (whatever way that is). However, I don't think any of those hypotheses is the case.

~~I think that comment is actually correct.~~ Eh, maybe, maybe not.

I think there's more than one package that provides a convert command and that those commands differ in what they accept.

SmokeDetector

02:55

[ SmokeDetector | MS ] Url-only title, bad keyword in body, bad keyword in title, blacklisted website in body, blacklisted website in title, +4 more (691): mumybear.org/keto-6x/ by vpwc on askubuntu.com

Zanna

03:53

@EliahKagan whaaat how is the shell going to expand it to match output files that are not there? That's the whole point of my answer...

Which I'm totally going to write... soon :/

Eliah Kagan

The input files are specified as name*.jpg.

The output files are also specified as name*.jpg.

Those will both expand the same.

It won't work, but those globs aren't going to be treated differently from one another by the shell.

Zanna

They have new_name*.jpg in output, no?

Eliah Kagan

No.

Zanna

Oh. Only in the answer

Eliah Kagan

Yeah.

The OP seems to want to convert the files in place. Part of what's going on is that they expect to be able to specify the same file as an input file and an output file. Some programs actually do work that way (though never with output redirection to the file, of course, which always truncates it before the program even runs). Others truncate the file and lose data. I don't know what convert does in this situation, in part because I don't know what program convert even is.

Zanna

04:00

In which case, I am not sure what they actually did

Darn

Eliah Kagan

On 16.04 I have:

ek@Io:~$ that convert
/usr/bin/convert
/etc/alternatives/convert
/usr/bin/convert-im6
../lib/x86_64-linux-gnu/ImageMagick-6.8.9/bin-Q16/convert

On 18.04 I have:

ek@Kip:~$ that convert
/usr/bin/convert
/etc/alternatives/convert
/usr/bin/convert-im6.q16

I imagine those are the same but with different organization of package files, but I don't know how many other packages provide /usr/bin/convert or what release the OP has.

Also there is the problem that the manpage and the output from --help seem to disagree about how to invoke it. On the same system:

ek@Kip:~$ man convert | head
convert(1)                                     General Commands Manual                                     convert(1)

NAME
       convert  -  convert  between image formats as well as resize an image, blur, crop, despeckle, dither, draw on,
       flip, join, re-sample, and much more.

SYNOPSIS
       convert [input-option] input-file [output-option] output-file

OVERVIEW

ek@Kip:~$ convert --help | head
Version: ImageMagick 6.9.7-4 Q16 i686 20170114 imagemagick.org
Copyright: © 1999-2017 ImageMagick Studio LLC
License: imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP
Delegates (built-in): bzlib djvu fftw fontconfig freetype jbig jng jpeg lcms lqr ltdl lzma openexr pangocairo png tiff wmf x xml zlib
Usage: convert-im6.q16 [options ...] file [ [options ...] file ...] [options ...] file

Image Settings:
  -adjoin              join images into a single multi-image file

Zanna

Hmm

Eliah Kagan

The manpage seems to indicate that multiple input or output filenames are not accepted, while the output with --help seems to indicate that they are.

I suspect that it's not the correct manpage and that it actually does, but even if so, that manpage is preusmably correct for something, and I don't know what the OP has installed.

The situation might be way simpler than I think it is, but I don't know the answer.

Natty

[ Natty | Sentinel ] 18.04 Software updater mystery package By: Mark17 5.0;

Eliah Kagan

04:16

@Natty tp

@Zanna Maybe apt-file can be used to find out what packages offer to provide a convert symlink in /etc/alternatives?

No, it doesn't seem to do that.

But I may have found the major possibilities. It seems /usr/bin/convert link, through the alternatives system, to a command provided by ImageMagick, or to a command provided by GraphicsMagick for the purpose of allowing users to invoke GraphicsMagick as though it were ImageMagick (I don't know the difference in syntax, but with GraphicMagick I believe one usually uses the gm command before actions like convert).

Zanna

I will give up trying to answer that

Eliah Kagan

04:33

I think giving up is reasonable but that there are three other approaches that make sense. I don't know how worthwhile they are.

The OP can be asked to provide more information about their convert command.

Testing can be done (this could be combined with more info from the OP).

Or another answer covering a single file conversion could be posted covering the globbing issues and proposing some alternative to a shell loop, such as using xargs.

@EliahKagan I've posted a comment (which I have since improved by editing).

Zanna