Check if filename is valid.

Hi, is there a native function or a simple code to check if a user-typed filename is valid for saving a file? (In that it doesn't contain illegal characters like /\":?<>|, etc.)

Answer 1

[Sean de Wolski]

regexp it!

[Qingyang]

So it would be like this?

if regexp(fname, '[/\*:?"<>|]', 'once')
  do something about it?
end

[Jan]

Let UIPUTFILE check the file name instead of using an edit control.

[Jason Nicholson]

This code snippet will not work unless you check if it is empty.

if ~isempty(regexp(filename, '[/\*:?"<>|]', 'once'))
        %Do something
end

[Voss]

You need to escape the backslash in the regular expression for that to work right:

~isempty(regexp('file\name','[/\*:?"<>|]', 'once')) % no match

ans = logical
   0

~isempty(regexp('file\name','[/\\*:?"<>|]', 'once')) % match

ans = logical
   1

Of course, on Windows, if absolute or relative path names are allowed, then backslash is a valid character, and if absolute path names are allowed, then colon is a valid character. On Mac/Linux, if absolute or relative path names are allowed, then slash is a valid character.

Answer 2

[Daniel Shub]

A long time ago, probably Windows 95 on a FAT16 harddisk, I started using the following:

regexp(fname, ['^(?!^(PRN|AUX|CLOCK\$|NUL|CON|COM\d|LPT\d|\..*)', ...
  '(\..+)?$)[^\x00-\x1f\\?*:\"><|/]+$'], 'once'));

At that time, Windows had the most restrictive file name conventions. I am not sure what the rules are now. You also should check for the length of the path and the total number of characters in the file name.

[Jan]

Windows 7: Either 260 characters, or start with //?/ and 32767 characters, while each folder can have up to 255 characters. The later works for most of the API-functions, but not e.g. for the Windows Explorer. Moving a file name with a long name to the RecycleBin fails also. The backup program and server based tools might fail also. Therefore I'd prefer the dull limit of 260 characters (including "C\:" and a trailing terminator '\0')!).

Answer 3

[ola bayo]

Which following is a valid file name in MATLAB?

A) lab 2
B) lab2
C) lab-2
D) 2lab
E) LAB 2

[Walter Roberson]

For the question as phrased: all of them. For a slightly different question, the answer would be fairly different.

Answer 4

[Thomas]

If you do not want to use UIputfile, another option is fopen. fileID = fopen(filename,'w') if fopen cannot open the file, then fileID is -1.

Answer 5

[Daniele Busi]

function bool = isLegalPath(str)
    bool = true;
    try
        java.io.File(str).toPath;
    catch
        bool = false;
    end
end

Answer 6

[George Abrahams]

Hi Qingyang, I recently released the isvalidpath function on File Exchange which does exactly this!

Like @Daniele Busi's answer, it's based on java.io.File().toPath, which is more robust than anything we'll build ourselves, but isvalidpath also provides:

• The option to validate that the path refers to a file, rather than a directory, or vice versa.
• The option to validate that the file extension matches a given set, for example, that the path refers to an image.
• Human readable feedback, in case the validation fails, for example, a warning that the path lacks a filename or contains an illegal character.