How can I check if I have read or write access to a directory?

When I do 

>> fileattrib('\\path\to\my\folder')

"UserRead" and "UserWrite" is "1" even though Windows Explorer shows that I do not have read or write access in the folder properties. Furthermore, when I try to read or write in the directory, it fails. Why does "fileattrib" indicate that I have read and write access even though I do not?

Answer 1

[MathWorks Support Team]

The "fileattrib" function is written as a wrapper for the DOS "attrib" command on Windows. "attrib" cannot do all the operations that you expect and checking read or write access for directories may not return the expected result. Therefore, when you do "fileattrib" on a directory, "UserRead" and "UserWrite" does not reliably report the read and write access to the directory in question. 

One workaround to check read access to a folder is:

exist( myfolder, 'dir' ) && ~isempty( dir( myfolder ) )

To check if the user has write permission:

fileName = '\\path\to\my\folder\tmpFile.txt';
[fid,errmsg] = fopen(fileName, 'w');
if ~isempty(errmsg)&&strcmp(errmsg,'Permission denied') 
    fprintf('\nError: You do not have write permission to the folder (%s).\n',fileName);
else
    fclose(fid);
    delete(fileName);
end

Disclaimer : The above script deletes the file. Please take a backup of the file before running the script

[Walter Roberson]

Not exactly. It is possible to have write access to an existing file without having write access to the directory, so 'a' vs 'w' is not exactly the same test. However the operating system documentation would have to be studied to find out whether requesting w access to an existing file is considered to be the same as deleting the file and recreating it. The POSIX answer would be No, that writing with 'w' keeps existing attributes while truncating the content, but Windows does not follow POSIX anymore.