Yeah, this is difficult, though not impossible, to get right with the inotify/kqueue api. Windows and mac do provide apis for recursive directory monitoring but

Yeah, this is difficult, though not impossible, to get right with the inotify/kqueue api. Windows and mac do provide apis for recursive directory monitoring but a cross platform tool will have to solve this problem. At a high level, the way to do it is to create an in memory representation of the file system that caches a watch handle for every file. When a deletion of a file is detected, you must create a watch on the parent directory, if there wasn't one already. Then you should be able to detect the ensuing create. To make this more concrete, the problem that a file watcher needs to solve is the problem of keeping its in memory representation of the file system consistent with the actual file system. Watch events are just a useful side effect of this process. The other fun part is that there is often a lag between the deletion and the create in the text editor case so it is necessary to defer triggering events when a deletion is detected and wait a little while to see if there is a corresponding creation. Otherwise you may rerun your command that depends on the file before it exists. It is possible to get like a 99+% solution to this problem without polling but it is a lot harder than what these simple tools, including entr do. The upshot is that file monitoring should be looked at as a lowest common denominator solution. A better solution is to build automatic command running into the text editor itself.