Issue #20891 has been reported by karasu (karasu k). ---------------------------------------- Bug #20891: Dir.foreach does not give a static list. https://bugs.ruby-lang.org/issues/20891 * Author: karasu (karasu k) * Status: Open * ruby -v: 2.7.0 * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN ---------------------------------------- I was using `Dir.foreach` with a block to batch change filenames. The sample code is something like this: ```rb look_up_table = File.open('look-up-table' ,'w') Dir.foreach('.').each_with_index do |file, index| File.rename(file, index) look_up_table << "#{file}: #{index}\n" end ``` As first I thought it's good, but I found that some indices might be missing. After staring at the look-up table for hours, I realised some files were modified more than once, and this is strange for me. It means that in each iteration of `Dir.foreach`, it acutally **might** fetch the files to see if there are new files that are not in the list before? What I mean **might** is that this situation does not occur anytime, I don't know how to or not to trigger it, but this is what I faced. I am aware that in `Dir.foreach` it might have some `yield` so this behavior might be normal for you guys, but since the function is called `foreach`, I assumed that it should give a list that is not gonna change once it's established. My later fix change to the sample code is: ```rb look_up_table = File.open('look-up-table' ,'w') Dir.foreach('.').to_a.each_with_index do |file, index| File.rename(file, index) look_up_table << "#{file}: #{index}\n" end ``` You can see that I add a `to_a` to change the result from `Dir.foreach` into an array, and rename those files according to it, instead of the result itself. I wonder if this is an old issue but I cannot find it anywhere else. Thanks in advance. Both English and Japanese are welcome! (I know that `Dir.foreach` will give `.` and `..` as well, but let's just forget it for now.) -- https://bugs.ruby-lang.org/