[ruby-core:87896] [Ruby trunk Misc#14905][Feedback] Strange behavior in Dir.glob using ** operator

Issue #14905 has been updated by mame (Yusuke Endoh).

Status changed from Open to Feedback

I cannot reproduce the issue on Linux.  What OS are you using?

```
$ ruby -v
ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]

$ find human_records/ cloud_records/ -type f
human_records/person2/other_records.yml
human_records/person1/records.yml
cloud_records/AWS/project2/records.yml
cloud_records/AWS/project1/records.yml
cloud_records/Azure/azproj1/records.yml

$ ruby -e 'p Dir.glob("human_records/**.{yml,yaml}")'
[]

$ ruby -e 'p Dir.glob("cloud_records/**.{yml,yaml}")'
[]
```

I think this pattern depends on a behavior of typical shells.  I'm unsure about the spec, but as far as I know, `**` is not used as a part of file name, but as a pattern that matches zero or more directories.  So you may want to use `**/*.yml`.

```
$ ruby -e 'p Dir.glob("human_records/**/*.{yml,yaml}")'
["human_records/person2/records.yml", "human_records/person1/other_records.yml"]

$ ruby -e 'p Dir.glob("cloud_records/**/*.{yml,yaml}")'
["cloud_records/AWS/project2/records.yml", "cloud_records/AWS/project1/records.yml", "cloud_records/Azure/azproj1/records.yml"]
```

----------------------------------------
Misc #14905: Strange behavior in Dir.glob using ** operator
https://bugs.ruby-lang.org/issues/14905#change-72908

* Author: trobinson (Trevor Robinson)
* Status: Feedback
* Priority: Normal
* Assignee: 
----------------------------------------
Hello,

I didn't want to report this as a bug because I'm not sure if it's intentional or not. The documentation didn't say either way. The `**` operator appears to work somewhat strangely when used in certain contexts.

An example setup to trigger the odd behavior looks something like this:
~~~ text
human_records
 ├ person1 ─ records.yml
 └ person2 ─ other_records.yml

cloud_records
 ├ AWS ┬ project1 ─ records.yml
 │     └ project2 ─ records.yml
 └ Azure ─ azproj1 ─ records.yml
~~~

Though the documentation doesn't say to do this, because of my experience with other globbing libraries, I did the following:

~~~ ruby
Dir.glob("human_records/**.{yml,yaml}")
# => ["human-records/person1/records.yml", "human_records/person2/other_records.yml"]

Dir.glob("cloud_records/**.{yml,yaml}")
# => []
~~~

So using `**` like this works if there is only one level of folders between the root and the target files, as if the glob was `"records/*/*.{yml,yaml}"`.

This seems like undefined behavior, so I thought I would bring it to your attention. If a change isn't a good solution to this, would a note in the documentation about undefined behavior around `**` be warranted?



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