Get path from OS X file reference URL alias (file:///.file/id=...) - macos

Question

In PyQt4 on Apple Mac OS X, we get a file reference URL to a drag-and-dropped file in the following format:
file:///.file/id=123456.78901
This, interestingly, is not a valid file URL, or at least it doesn't transparently resolve in most applications — there is no /.file/id=... file in the filesystem.
Using just shell, how do I dereference this NSURL or file reference or alias (or whatever it's called) into a valid path to file on the filesystem?

Answer 1

In Swift you can use URL.standardized to get the valid path from a reference URL. So in Swift 4 - to get the file name from a drag-and-dropped file you'd do something like...
let fileType = NSPasteboard.PasteboardType (kUTTypeFileURL as String)
extension NSPasteboardItem {
func fileURL ()->URL? {
if let refURL = self.string(forType: fileType) {
return URL (fileURLWithPath: refURL).standardized
}
return nil
}
}

Answer 2

One can use osascript, an AppleScript interpreter available on default OS X installs, run with the following script:
osascript -e 'get posix path of posix file "file:///.file/id=123.456" -- kthxbai'
Prints /Users/josh/Downloads/paste-10837081.py.

Answer 3

That is a NSURL object, to get a path from it:
NSString *filePath = [fileURL path];

Answer 4

This can also be accomplished in Python using the PyObjC bridge.
from Foundation import NSURL # depends on PyObjC
# convert a URL file reference to a POSIX path
NSURL.URLWithString_('file:///.file/id=6571367.8602676692').path()
# convert a path file reference to a POSIX path
NSURL.fileURLWithPath_('/.file/id=6571367.8602676692').path()
Be sure you to select the appropriate NSURL method for your data type or else you'll get the wrong value back.
Resources
NSURL API doc
API discussion of file reference URLs
PyObjC