Strange behavior retrieving directories' names with dir

Question

Adriano 2011-9-30

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https://ww2.mathworks.cn/matlabcentral/answers/17116-strange-behavior-retrieving-directories-names-with-dir

I am trying to extract the names of the subdirectories contained in one directory. For example:

   mainDirectory
      matlabScript.m
      results
         subdirectory1
         subdirectory2
         subdirectory3
         subdirectory4

I am running the following in matlabScript.m :

subdirectories = dir([pwd filesep results filesep]);

In theory, I should get a structure with 4 elements, one for each subdirectory. However, I am getting 6 elements. Of these, 4 are the desired subdirectories, but the other two are two mysterious subdirectories:

       name: '.'
       date: '30-sep-2011 10:09:14'
      bytes: 0
      isdir: 1
    datenum: 7.3478e+005
       name: '..'
       date: '27-sep-2011 19:51:12'
      bytes: 0
      isdir: 1
    datenum: 7.3477e+005

I am pretty sure I do not have this directories. I already read the documentation of dir ant nothing is stated. I also changed the OS properties to show any hidden folders and not even with that I found them. How can I correct this strange behavior? I am running MATLAB R2010b in a computer with Windows 7, 64 bits.

Thanks in advance

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Answer 1

Jan 2011-9-30

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Some modifications: cd is faster than pwd, the trailing file separator is not needed, fullfile is smarter than [cd, filesep, results], because it considers the already existing separator in e.g. "C:\":

subdirectories = dir(fullfile(cd, results));

If you want to exclude all files and folders starting with a dot -e.g. a common method under Unix:

subdirectories(strncmp({subdirectories.name}, '.', 1)) = [];

To remove only "." and "..":

subname                        = {subdirectories.name};
subname(strcmp(subname, '.'))  = [];
subname(strcmp(subname, '..')) = [];

Although these two directories have been the first and second entries in the list in all of my tests under Windows95 to Windows7, Suse-Linux, MacOS7/8/9/X, AUX and AIX, I would not rely on this, but use astring comparison always.

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Walter Roberson 2011-9-30

The directory order is not defined by dir(), and depends upon the properties of the underlying file system. If the filesystem is one that does not happen to put . and .. first, then dir() will not return them as the first two entries.

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