migrating 2.8 bash scripts to gimp 3

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migrating 2.8 bash scripts to gimp 3 - vince - 03-09-2026

Hello,
new to this forum I hope someone here could help me a little bit.

As I upgraded from debian 12 to debian 13, gimp was upgraded to version 3.
I have a set of short scripts that allowed me to invoke gimp (at least until version 2.8) from a linux bash console. Now they fail, so I have to adapt them to recent changes.

The one question I still stumble on is the ability to set a drawable in my image. The former syntax does not work anymore :

Code:

(drawable (car(gimp-image-get-active-drawable image)))

so that I can't do anything on a specific layer e.g. desaturate :

Code:

(gimp-drawable-desaturate drawable 0)

How can I instruct gimp that, let's say, the drawable is layer [0] ?

Thanks in advance,
Vince.

RE: migrating 2.8 bash scripts to gimp 3 - programmer_ceds - 03-09-2026

(03-09-2026, 11:53 AM)vince Wrote: Hello,
new to this forum I hope someone here could help me a little bit.

As I upgraded from debian 12 to debian 13, gimp was upgraded to version 3.
I have a set of short scripts that allowed me to invoke gimp (at least until version 2.8) from a linux bash console. Now they fail, so I have to adapt them to recent changes.

The one question I still stumble on is the ability to set a drawable in my image. The former syntax does not work anymore :

Code:

(drawable (car(gimp-image-get-active-drawable image)))

so that I can't do anything on a specific layer e.g. desaturate :

Code:

(gimp-drawable-desaturate drawable 0)
How can I instruct gimp that, let's say, the drawable is layer [0] ?

Thanks in advance,
Vince.

In this case you need gimp-image-get-selected-drawables which returns a list of the selected drawables.

Use "Help/Procedure Browser" to search for key words in the functions that you need to updated.

Also looking at the built-in scripts may help you.

RE: migrating 2.8 bash scripts to gimp 3 - vince - 03-09-2026

(03-09-2026, 04:33 PM)programmer_ceds Wrote: In this case you need gimp-image-get-selected-drawables which returns a list of the selected drawables.

Use "Help/Procedure Browser" to search for key words in the functions that you need to updated.

Also looking at the built-in scripts may help you.

Thank you for your help,

yes, I've struggled with this solution, but it seems there's something I don't do the right way to handle the array of drawables.
This works:

Code:

gimp -i --quit --batch-interpreter=plug-in-script-fu-eval -b \

"(\

    let*(\

        (image (car (file-png-load 1 \"input.png\")))\

    )\

    (gimp-file-save 1 image \"output.png\")\

)"

but this:

Code:

gimp -i --quit --batch-interpreter=plug-in-script-fu-eval -b \

"(\

    let*(\

        (image (car (file-png-load 1 \"input.png\")))\

        (drawable (vector-ref (gimp-image-get-selected-drawables image) 0))\

    )\

    (gimp-file-save 1 image \"output.png\")\

)"

throws me the following error:

Code:

Error: vector-ref: argument 1 must be: vector

I'm sorry in advance for my poor knowledge of this Scheme syntax...

RE: migrating 2.8 bash scripts to gimp 3 - MrsP-from-C - 03-09-2026

looking at GIMP's inbuilt scripts it could possibly be

Code:

(drawable (vector-ref (car (gimp-image-get-selected-drawables image)) 0))

RE: migrating 2.8 bash scripts to gimp 3 - rich2005 - 03-09-2026

100% not script-fu fan but I have come across that vector error before so trying this in a Mint 22.3 / Gimp 3.0.8 (from PPA).
Works but throws up warnings.

Quote:rich@rich-3:~$ gimp -i --quit --batch-interpreter=plug-in-script-fu-eval -b \
"(\
let*(\
(image (car (file-png-load 1 \"input.png\")))\
(drawable (vector(gimp-image-get-selected-drawables image) 0))\
)\
(gimp-file-save 1 image \"output.png\")\
)"

(script-fu:3401): scriptfu-WARNING **: 18:40:58.393: Calling Plug-In PDB procedures with arguments as an ordered list is deprecated.
Please use named arguments: (file-png-load #:run-mode 1 #:file input.png)

(script-fu:3401): scriptfu-WARNING **: 18:40:58.476: Missing arg type: GimpExportOptions
batch command executed successfully
INFO: a stray image seems to have been left around by a plug-in: "[output] (exported)"rich@rich-3:~$

Just a remark, but an option for Gimp 3 is the batcher plugin https://kamilburda.github.io/batcher/ It is remarkably flexible for processing files and images with layers.

RE: migrating 2.8 bash scripts to gimp 3 - vince - 03-09-2026

(03-09-2026, 06:50 PM)rich2005 Wrote:

Code:

rich@rich-3:~$ gimp -i --quit --batch-interpreter=plug-in-script-fu-eval -b \ "(\ let*(\ (image (car (file-png-load 1 \"input.png\")))\ (drawable (vector(gimp-image-get-selected-drawables image) 0))\ )\ (gimp-file-save 1 image \"output.png\")\ )"

(03-09-2026, 06:37 PM)MrsP-from-C Wrote:

Code:

(drawable (vector-ref (car (gimp-image-get-selected-drawables image)) 0))

Thank you for these solutions! both suggestions succeed.

Perhaps did I miss it, is there an official documentation for the Scheme syntax? or should we just rely on a bunch of examples?

Happy to have landed on gimp-forum, thanks again.
V.

(03-09-2026, 08:25 PM)vince Wrote: Thank you for these solutions! both suggestions succeed.

but then...

Code:

gimp -i --quit --batch-interpreter=plug-in-script-fu-eval -b \

"(\

    let*(\

        (image (car (file-png-load 1 \"input.png\")))\

        (my-drawable (vector(gimp-image-get-selected-drawables image) 0))\

    )\

    (gimp-drawable-desaturate my-drawable 0)\

    (file-png-export 1 image \"output.png\")\

)"

gimp still complains, and once again I can't figure out what is going wrong. The error is:

Code:

Error: in script, expected type: numeric for argument 1 to gimp-drawable-desaturate

Does this mean that gimp-drawable-desaturate expects a number (sort of index of drawables) instead of my declared my-drawable layer?
I'm puzzled.

RE: migrating 2.8 bash scripts to gimp 3 - vince - 03-09-2026

Sorry for the previous message, I got lost. Here is a working solution (that from MrsP-from-C):

Code:

gimp -i --quit --batch-interpreter=plug-in-script-fu-eval -b \

"(\

    let*(\

        (image (car (file-png-load 1 \"input.png\")))\

        (my-drawable (vector-ref (car (gimp-image-get-selected-drawables image)) 0))\

    )\

    (gimp-drawable-desaturate my-drawable 0 )\

    (file-png-export 1 image \"output.png\")\

)"

Now, I notice the good old plug-in-colortoalpha is absent from the procedure browser. Sad

RE: migrating 2.8 bash scripts to gimp 3 - MrsP-from-C - 03-10-2026

As you asked for official documentation ....
Some is here: https://developer.gimp.org/resource/script-fu/

Maybe Mark Sweeney's site might help you:
https://script-fu.github.io/funky/

Most helpful is just to look at the scripts that ship with GIMP.

RE: migrating 2.8 bash scripts to gimp 3 - vince - 03-10-2026

(03-10-2026, 06:50 AM)MrsP-from-C Wrote: As you asked for official documentation ....
Some is here: https://developer.gimp.org/resource/script-fu/

Maybe Mark Sweeney's site might help you:
https://script-fu.github.io/funky/

Most helpful is just to look at the scripts that ship with GIMP.

Nice, the road is actually long and steep!

Do you have any suggestion about the missing plug-in-colortoalpha?
I can't find where I read it was now a GEGL filter. Is there a simple way to run such command in a "one-liner" script?

V.

RE: migrating 2.8 bash scripts to gimp 3 - MrsP-from-C - 03-10-2026

Looks like it's a GEGL Operation now:
https://gegl.org/operations/gegl-color-to-alpha.html

No idea how to handle those in script-fu.
But you'll find examples for similar procedures in clothify.scm, if you search for gegl: