Trimming directory ('Pfad') name

The action (Quick)

Action Type: Replace
Field: '_DIRECTORY' ("Pfad", 2nd colum from left)
Original: 'D:'
Replace with: '' (nothing)

does not trim the path names at the beginning. What do I miss here?

Regards
Jens11

_DIRECTORY is a read-only information field and doesn't refer to the full path, only the immediate directory.

_PATH is probably what you want to change, but it is also read-only.

What is the purpose of changing either of these information-only fields?

The field is on display in my car audio. So I would lke to use it for information.

It seems strange that it would display on car audio unless it attaches via Bluetooth to your phone. Sorry, there is no way to change it in Mp3Tag as it is populated on the fly by the device accessing the file.

It does not seem logical that these fields are available as targets in the REPLACE and FORMAT VALUE actions. It works because Mp3Tag will change the path if it can. Your REPLACE failed because the _PATH could not be changed. Without a drive letter or other acceptable prefix, it won't work.

Another point is that "D:" never shows in the _DIRECTORY field unless it is the root directory. I haven't tested that, but it would make sense on a flash drive.

Yes, it is a USB stick.

Thank you for your explanations which are plausible and helpful to me. May I add a question which is somewhat off topic?
I am familiar with mp3tag's options to write content into fields by actions and quick actions. But if I want to edit just one tag in one file - e. g. 'Title' - the action feature seems overdimensioned to me. Is there a more direct way? Going through the menue I found none.

My off topic has taken care of itself. I found the tag panel now.

In general, _DIRECTORY is not a read-only field and is definitely writable.

It can be tested like this:
Create a file with this path: "D:\OriginalDirectory\file.mp3"
Change the directory with this action: Action Type: Replace

Field: _DIRECTORY
Original: Original
Replace with: New

Observe the file's new path: "D:\NewDirectory\file.mp3"

Also, every other file and subfolder in "D:\OriginalDirectory" will be moved to "D:\NewDirectory" and "D:\OriginalDirectory" will be deleted.

But in the special case presented by the OP, it is impossible to rename the _DIRECTORY field because the file is in the root directory, as Rijkstra explained.
If a file exists in the root of drive D, without any other containing folder, %_DIRECTORY% is D: (without a trailing backslash) so replacing D:\ would fail.
And if you tried to replace D: with "" (nothing) it is like saying "delete the drive D" which Mp3tag will not (cannot?) do, thankfully. Nor will it change the drive letter.

Just to be clear: %_DIRECTORY% is not the same as what is shown as "Directory:" in the tag panel.
%_DIRECTORY% is only the name of a file's containing folder.

I guess what was meant is that "D:" never shows; backslashes never show in the _DIRECTORY field.

It would seem that your tag panel is closed. It should be on the left. Ctrl+Q will open it. It's on the View Menu, along with Extended Tags. You can edit the displayed fields directly also.

Is it really user writeable? If Mp3Tag successfully changes the directory, isn't the new location read into it? A failure will leave it as is. What I mean by being writeable is that if the file is moved outside Mp3Tag, the new location will show up in the _DIRECTORY field when it is reopened. So the field is really only written by the location of the file.

And the location of the file can be changed from within Mp3tag, by writing to the _DIRECTORY field.
Therefore, it is writable: just as if you changed the directory name in the file system.

Thank you all for your helpful comments!
I may add a comment which could be appreciated by mp3tag newbies:

My music collection has come into beeing before I found mp3tag. The full path of every piece of music contained all important information in a well structured manner. The tags remained empty in most cases. So the file managers of my computers were sufficient instruments to adminstrate the files. However this was not satisfactory on my car audio with an USB stick.

mp3tag and the knowledge of of some elements of the regex language allowed me retrieve the suitable parts of the path and adapt them to the car display. This is done by an action group of six or seven actions. They are executed by one mouse click - processing one file or many of them.

Regards and compliments to the creator of mp3tag
Jens11