IM 7 command-line tools don't understand the -- option

[deflate]

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$ identify -ping -- image.jpg
identify: unrecognized option `--' @ error/identify.c/IdentifyImageCommand/920.

IM 6.x did.

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$ identify --version
Version: ImageMagick 7.0.7-19 Q16 x86_64 2018-03-17 http://www.imagemagick.org
Copyright: © 1999-2018 ImageMagick Studio LLC
License: http://www.imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP 
Delegates (built-in): cairo djvu freetype jng jpeg lcms ltdl pangocairo png rsvg tiff x xml zlib

[snibgo]

IM v7 has a different, more strict command interpreter than v6.

Is "--" a documented feature?

[deflate]

"--" is the standard unix way of telling a program that there will be no "-X" or "--XXX" (replace X and XXX with any letter/word) options after it. Sometimes filenames start with a hyphen, so "--" is essential to prevent confusion.

[snibgo]

Yes. The common unix convention for program arguments is to list options and then filenames, and "--" prevents programs from thinking that filenames that start with "-" are options. This is great for "filter" programs that have exactly one input and one output.

But ImageMagick can take any number of input and output filenames (eg 10,000), with options that apply to some filenames, and options that apply to intermediate results, and so on. So IM adopted a convention more like a programming language, where all operations (including reading and writing files) are given in the order they should be performed.

With that convention, leaving the filenames to the end makes no sense.

IM v6 didn't enforce that convention, and still accepted the unix format of leaving filenames to the end.

IM v7 does enforce the sequencing order, so "--" is redundant.

Sadly (in my view), IM distinguishes between filenames and options by "-", so filenames usually cannot start with "-". However, IM v7 has explicit read and write operations, so we can do this:

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magick -read rose: -write -x.png -exit

magick -read -x.png x2.png