Ubuntu – GIMP 2.8 doesn’t allow to save usual image file formats (jpg, png) via Save dialog

For my workflow here the definitely fastest way to safe an edited file back to the path it resides is using the "File -> Overwrite xxx" menu which appears after an existing file was edited:

To further speed things up we can also define a key shortcut for file-overwrite which, after removing the shortcut for file-save could also be Ctrl + S :

You cannot use %F twice in a command like that, because %F gets replaced by the names of every file selected. For example, a command of sh with parameters -c 'printf "%%s\n" "$@" > foo' %F %F will create a file named foo with the names of every file selected, twice. Therefore the convert command that actually runs is:

convert file1.jpg file2.jpg ... -quality 80% file1.jpg file2.jpg ... fileN.jpg-80q.jpg

And since the last file is taken to be the output file name, only it will matter.

What you can do is wrap your command in bash -c and run a for loop:

bash -c 'for i; do convert "$i" -quality 80% "${i/%.jpg/-80q.jpg}"; done'

(where I am assuming that all files end with .jpg)

In an action, you will have bash as the command, and for the parameters:

-c 'for i; do convert "$i" -quality 80%% "${i/%%.jpg/-80q.jpg}"; done' - %F

You can make this more complicated to handle any extension, at which point you might as well skip Actions and use scripting.