What are the usecases for this? Not sure if it should be in the standard library.

And also, this implementation could be alot improved on performance. It should open the file just once, move to the end of file and try to read periodically until it does not read EOF. Also, only sleep if there is nothing more to read. The way you did it works, but will be extremely slow when the file is huge.

inotify could be used on systems that support it to avoid the sleep.

A better name would be follow_tail. Simply tail makes me think it returns the last N lines and done.

@lbguilherme My thoughts exactly

I can imagine tail as a command line application, but I don't know when this would be useful as a method to use in a program. And, in any case, it can be provided as a separate shard.

(which already exists: https://github.com/Thor77/tail.cr)