GNU bug report logs - #46550
bug in diff -r?

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Stan Schymanski <schymans <at> gmail.com>
To: bug-diffutils <at> gnu.org
Subject: bug in diff -r?
Date: Mon, 15 Feb 2021 22:56:38 +0100

Dear all,

I cannot get diff -r to search recursively. Here is an example. First I
create two folders, each with one sub-folder and one file, where each
sub-folder and file has a different content:
```
$ mkdir orig
$ mkdir backup
$ mkdir orig/1
$ mkdir backup/2
$ echo 'blah' > orig/1/test.txt
$ ls orig/1
test.txt
$ echo 'blah1' > backup/2/test1.txt
```
Now I compare them using the '-qr' option:

```
$ diff -qr orig/ backup/
Only in orig/: 1
Only in backup/: 2
```
I was expecting to be told that orig/1/test.txt and backup/2/test1.txt
are unique. If I descend into the subfolder in one of them, the file in
that folder is found:
```
$ diff -r orig/1 backup/
Only in backup/: 2
Only in orig/1: test.txt
```
I actually get the same behaviour with or without '-qr'. Is this a bug
or am I misunderstanding diff -r? I am using diff (GNU diffutils) 3.7.

Cheers
Stan

Message #8 received at 46550 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Stan Schymanski <schymans <at> gmail.com>, 46550 <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#46550: bug in diff -r?
Date: Tue, 16 Feb 2021 09:22:22 -0800

On 2/15/21 1:56 PM, Stan Schymanski wrote:
> Is this a bug
> or am I misunderstanding diff -r?

Perhaps a bit of both. The algorithm you want (which is to pretend that 
directories missing in A are empty in B, and vice versa) is not the 
algorithm that 'diff -r A B' uses.

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