This is an example I use to find photos I've stripped the exif data from and tagged:

    mdfind -onlyin . 'kMDItemUserTags=exif-stripped'

ohhh thanks, this is something I needed to know.

linux has xattr too. so technically, our filesystems already support tags.

that means it is now up to the other tools to catch up and make use of them.

here is a discussion about tags and extended attributes in gnome. https://blog.chipx86.com/2005/12/07/tagging-and-the-gnome-de...

it is from 2005, so not really current, but the arguments are interesting.

in short: filesystem attributes are systemwide (but you and i may want to have different tags on the same shared file) and the user needs to have permission on the files, so you can't tag files that you can read but can't change.

i believe these issues are solvable, esp. the latter would work if we have permissions to add tags but not the content of a file. (like you can rename a file even if you don't have write permission to the file)

xattrs can certainly be used to store tagging info. There are a couple major problems with them though. 1) xattrs are not supported by all file systems and they are not enabled by default in some. If you copy a file with xattrs from one file system to another that either doesn't support them or didn't enable their use, then your xattrs are thrown away in the copy. 2)Searching for files based on xattrs in a large folder tree (e.g. several million files across thousands of folders) is exceptionally slow by nature.

right, but the alternative is no support for tags at all, so xattr gets us halfway there, and filesystems that don't have it need to keep up.

searching can be sped up by building an index. apps that want to use tags will need to do that, just like they build an index of files already. because searching filenames is also slow.

a version of locatedb that supports xattr would help for example, see https://en.wikipedia.org/wiki/Desktop_search