Issue #19441 has been updated by stac47 (Laurent Stacul). Thanks nobu for your answer it makes perfect sense. My case which led to the current question comes from a Rails application which has a controller receiving a file. My input `params[:file]` hold an `ActionDispatch::Http::UploadedFile` which itself has an attribute `tempfile`. In the controller, `params[:file]` is passed to some functions (I don't have the control of) that can read and close the underlying `tempfile`. As a matter a fact, the code calls `ActionDispatch::Http::UploadedFile#open` (shortcut to `tempfile#open`) after the calls that close the file. I was wondering whether I could avoid calling `#open` by providing the methods which can close the file with a `dup`ed file descriptor so that the original `ActionDispatch::Http::UploadedFile` is left untouched until I really use it in my own code. The scenario in itself is not really interesting, it is just I was surprised by the behaviour when I used `Tempfile#dup` but your explanation is acceptable. Thanks for this. ---------------------------------------- Bug #19441: Closing an Tempfile#dup behaviour https://bugs.ruby-lang.org/issues/19441#change-101930 * Author: stac47 (Laurent Stacul) * Status: Open * Priority: Normal * ruby -v: ruby 3.2.1 (2023-02-08 revision 31819e82c8) [x86_64-darwin20] * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- Hello amazing ruby folks! I classified that ticket as a "Bug" although it is perhaps something I did not understand. Here is a ruby session: ``` ruby irb(main):001:0> file = Tempfile.new => #<File:/var/folders/m2/bljzrgq160vbf0vk466k_7gw0000gn/T/20230216-39664-davfmj> irb(main):002:0> file.fileno => 9 irb(main):003:0> dup = file.dup => #<File:/var/folders/m2/bljzrgq160vbf0vk466k_7gw0000gn/T/20230216-39664-davfmj> irb(main):004:0> dup.fileno => 10 irb(main):005:0> dup.close => nil irb(main):006:0> dup.closed? => false irb(main):007:0> file.closed? => true ``` The two last lines are unexpected to me. I would have expected the converse: ```ruby irb(main):006:0> dup.closed? => true irb(main):007:0> file.closed? => false ``` I tried this scenario in latest ruby but also in ruby 2.7. Thanks in advance for helping me to understand this behaviour. -- https://bugs.ruby-lang.org/