why I cannot list specify files with function dir

I want to list all special files with specified extensions, such as all *.jpg files. I cd the matlab to the current folder, and call the dir function as following:

dir *.jpg

it does not return all file names but a struct with name attribute and other fields, like the following picture showing

If I call dir function as following:

dir

it will return all files

I just want to list all jpg files, but not including the root directory, how to use dir function, please?

[Stephen23]

"If I call dir function as following:"

dir

"it will return all files"

Not at all: it does not return anything, it simply lists them in the command window. Have a look in your workspace, and you won't find any variable being returned by dir. This is the difference between a function returning an output, and a function displaying something in the command window, which are are two totally different things. Every instance of dir being called without an output argument simply displays/lists something in the command window, and nothing is returned. If you want to assign its output to an argument then this output will be a structure, as you have already observed.

[li yan]

yes, I test the function of "dir" in command window. If I assign its outputs to an argument, like this:

s = dir;

the output s is a struct stores all file names and other attributes. But in my current folder, I just want to get all jpg file names, according to the help document, I write the code like this:

s = dir('*.jpg');

this does not return all jpg files to the argument s, this make me confused.

[Guillaume]

Using the same directory as in your screenshot what is the output of:

s = dir;
double(s(10).name(end-4:end))  %extension of arbitrary file number 10

[li yan]

the result is

ans =

    56    46   106   112   103

the following is my experimental code:

and the following is the help document, i'm confused that I cant get specified files using wildcards(*).

[Guillaume]

This is indeed very odd.

Which version of matlab are you using? Looks like an old version from your help screenshot.

What is the output of:

s = dir;
jpgfiles = s(~cellfun(@isempty, regexp({s.name}, '\.jpg$')));
numel(jpgfiles)

[Guillaume]

Actually, when you sow the output of

>>dir

can you show the entire list of files? Is there actually a file that looks like *.jpg

[li yan]

My matlab version is Matlab2015b (8.6.0.267246). I type the code you put, the result is as following:

actually, my current folder contains jpg files and dir can list all jpg files shown above the screen shot.

if s = dir; it works well, but s = dir('*.jpg'); it does not work

[Guillaume]

I wanted to see the end of the list of files. From the screenshot you show in KSSV answer, it looks like somehow you have a file actually called '*.jpg' in that directory. Something I didn't think was possible on Windows.

What is the output of

s = dir('*.jpg');
double(s.name)

[li yan]

It's really odd. I copy 3 pictures to another folder, and test like this:

s = dir('*.jpg');

it works well, it means that the variable s really stores 3 picture information as a struct. But if I copy all pictures to the folder, and re-test like above, it does not work well.

I'm sure that the folder does not contain a file named *.jpg.

last, I test dir in the current folder contains all files ( there is no file named *.jpg, I'm sure) using your code:

s = dir('*.jpg');
double(s.name)

the result is 42 46 106 112 103

Answer 1

[Jan]

Guillaume is right: You have created a file called '*.jpg'. This is not possible under Windows with standard tools, but you can do this under Linux or with using evil tricks. I suggest to start your machine from a Linux live CD or USB stick and delete the file '*.jpg'.

You can install the Linux subsystem: https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/cc771470(v=ws.11) (here for Windows 7) and delete the file from there.

This works for a trailing dot in the file name, which is illegal also:

system('del \\?\D:\Temp\asd.')

I cannot test this with a * in the name, because I'm not able to create such a file...

A chkdsk might fix the file name also.

[Guillaume]

This is why I wanted a screenshot of the end of the file listing. Everything points to a file called *.jpg in the current directory.

How you would create such a file in Windows is a mystery. The WIN32 API won't let you. I suggest copying all the valid files into a new directory then deleting the current directory with the invalid *.jpg file (if the OS actually lets you).

[li yan]

Thank you for your help very much.

I do not know why there is a *.jpg file in the folder, even though I cannt see that file from explorer.

Answer 2

[KSSV]

images = dir('*.jpg') ;
iwant = {images(:).name}' ;

[li yan]

it does not work correctly.

images = dir('*.jpg') ;

this just return a struct with one element, like this: