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List: coreutils-bug
Subject: bug#11271: dirname /home/dir/
From: Eric Blake <eblake () redhat ! com>
Date: 2012-04-18 17:35:23
Message-ID: 4F8EFB5B.1070308 () redhat ! com
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tag 11271 notabug
thanks
On 04/18/2012 05:01 AM, Kevin Huanpeng Du wrote:
> Hi,
> i find dirname dirname strip a dir name when a string with out a filename.
>
> ₤ dirname /dir/file
> ₤ /dir
> ₤ dirname /dir/subdir/
> ₤ /dir # is this right? subdir is a not a file.
Thanks for the report. However, this is not a bug. POSIX requires this
behavior. In POSIX parlance, a "file" is any entity that can be
referenced by name as a member of a directory. There are multiple types
of files: regular files, block device files, character device files,
sockets, and important to your case, subdirectories. Only
subdirectories may have a trailing slash, but the point remains that
even without the trailing slash, 'subdir' is a file (of type directory,
rather than the more typical type regular file), which can be referenced
by name from the directory '/dir'.
The POSIX-mandated algorithm for the dirname executable is to strip
trailing slashes _before_ removing the trailing file name element,
precisely for usage like this:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/dirname.html
1 If string is //, skip steps 2 to 5.
2 If string consists entirely of <slash> characters, string shall be
set to a single <slash> character. In this case, skip steps 3 to 8.
3 If there are any trailing <slash> characters in string, they shall
be removed.
4 If there are no <slash> characters remaining in string, string
shall be set to a single <period> character. In this case, skip steps 5
to 8.
5 If there are any trailing non- <slash> characters in string, they
shall be removed.
6 If the remaining string is //, it is implementation-defined whether
steps 7 and 8 are skipped or processed.
7 If there are any trailing <slash> characters in string, they shall
be removed.
8 If the remaining string is empty, string shall be set to a single
<slash> character.
And according to that algorithm, even though '/dir/subdir',
'/dir/subdir/' and '/dir/subdir/.' all resolve to the same location in
the file system, using dirname on the first two gives '/dir' while using
'dirname /dir/subdir/.' gives '/dir/subdir'.
--
Eric Blake eblake@redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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