i want to validate a folder name , it should not start with a number , or any special character, i am not sure about what special symbols are allowed inside folder names , kindly help .

here is my function

function validateFileName() { 
    var re = /[^a-zA-Z0-9\-]/;

      if(!re.test($('#new_folder_name').value)) {
          alert("Error: Input contains invalid characters!");
          $('#new_folder_name').focus();
          return false;
        }

        // validation was successful
        return true;
      }

i want to validate a folder name , it should not start with a number , or any special character, i am not sure about what special symbols are allowed inside folder names , kindly help .

here is my function

function validateFileName() { 
    var re = /[^a-zA-Z0-9\-]/;

      if(!re.test($('#new_folder_name').value)) {
          alert("Error: Input contains invalid characters!");
          $('#new_folder_name').focus();
          return false;
        }

        // validation was successful
        return true;
      }

• javascript
• jquery
• regex
• validation

• What are you validating the folder for? Your server where you know what OS is running and as such can tell what is valid, or a client puter with who knows what OS? – DGS Commented Aug 10, 2015 at 10:37
• You can find info about which characters are not legal to use here support.microsoft./en-us/kb/177506 – Johan Commented Aug 10, 2015 at 10:37
• i am creating a new folder and i want a validation on that folder name so that user cannot enter malicious characters while providing name for folder i am not getting how to do it – Anky Commented Aug 10, 2015 at 11:22
• "what special symbols are allowed inside folder names" — It depends on which file system you are using. – Quentin Commented Aug 10, 2015 at 11:26
• Name of a folder is based on what file system you use. Each OS has different file system. So, you have to take care of OS, file-system conditions before you validate. Adding to that, file system itself checks if the name is valid or not and you get exceptions for invalid folder name anyway. So, handle the exception and show it to the user. – bozzmob Commented Aug 10, 2015 at 11:36

3 Answers 3

As per the Naming Files, path and Namespaces article by MSDN

The following special characters are reserved:

< (less than)
> (greater than)
: (colon)
" (double quote)
/ (forward slash)
\ (backslash)
| (vertical bar or pipe)
? (question mark)
* (asterisk)

And the following keywords are also reserved

CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9. 

Which are case incensitive.

So considering those facts, the possible regex can be:

[^<>:"/\|?*(?:aux|con|nul|prn|[1-9]|lpt[1-9])]

So your transformed function will be

function validateFileName() { 
    var re = /[^<>:"/\|?*(?:aux|con|nul|prn|[1-9]|lpt[1-9])]/;

      if(!re.test($('#new_folder_name').value)) {
          alert("Error: Input contains invalid characters!");
          $('#new_folder_name').focus();
          return false;
        }

        // validation was successful
        return true;
      }

Just check for the folder name starts with a letter and does not start with . (Dot)

var re = /^[a-zA-Z].*/;
re.test(folder_name);

This would return true only if the folder name starts with a letter.

In C#, there is a function that returns the list of invalid path symbols. Also the Naming Files, Paths, and Namespaces lists some reserved characters that cannot be used in both folder and file names. Here is the regex covering all these restrictions:

var RealInvalidPathChars = /[<>:"\/\\|?*\x00-\x1F]/;

You can test for any of the symbols inside a string, and it will be an invalid path.

Also, there is a list of reserved words that cannot be used as folder names, and we can also use them in a regex:

/^(?:aux|con|clock\$|nul|prn|[1-9]|lpt[1-9])$/i

If this regex check returns true, the path is invalid.

Here is a snippet bining all these:

$( "#new_folder_name" ).submit(function( event ) {
    var rx = /[<>:"\/\\|?*\x00-\x1F]|^(?:aux|con|clock\$|nul|prn|[1-9]|lpt[1-9])$/i;
    if(rx.test($( "input:first" ).val())) {
      alert("Error: Input contains invalid characters!");
   }
});

<script src="https://ajax.googleapis./ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form id="new_folder_name">
  <input type="text" value="<INVALID>">
  <input type="submit" value="Go">
</form>