NT Syntax


Display or change the association between a file extension and a fileType

   ASSOC .ext = [fileType]


   ASSOC .ext

   ASSOC .ext = 

    .ext      : The file extension
    fileType  : The type of file 

A file extension is the last few characters in a FileName after the period.
So a file called JANUARY.HTML has the file extension .HTML

The File extension is used by Windows NT to determine the type of information stored in the file and therefore which application(s) will be able to display the information in the file. File extensions are not case sensitive and are not limited to 3 characters.

More than one file extension may be associated with the same File Type.
e.g. both the extension .JPG and the extension .JPEG may be associated with the File Type "jpegfile"

At any one time a given file extension may only be associated with one File Type.
e.g. If you change the extension .JPG so it is associated with the File Type "txtfile" then it's normal association with "jpegfile" will disappear. Removing the association to "txtfile" does not restore the association to "jpegfile"

File Types can be displayed in the Windows Explorer GUI: [View, Options, File Types] however the spelling is usually different to that expected by the ASSOC command e.g. the File Type "txtfile" is displayed in the GUI as "Text Document"and "jpegfile" is displayed as "image/jpeg"

The command ASSOC followed by just a file extension will display the current File Type for that extension.

ASSOC without any parameters will display all the current file associations.

ASSOC with ".ext=" will delete the association for that file extension.

Using this command will create or change values in the registry at HKCR\\ .<file extension>


Viewing file associations:

ASSOC .txt
ASSOC .doc
ASSOC >backup.txt

Editing file associations:

ASSOC .txt=txtfile
ASSOC .DIC=txtfile
ASSOC .html=Htmlfile

Deleting a file association:

ASSOC .html=

"Of all forms of caution, caution in love is perhaps the most fatal to true happiness" - Bertrand Russell

Related Commands:

FTYPE - Edit file types (used in file extension associations)
Batch file to list the application associated with a file extension
ASSOCIAT - One step file association (Resource Kit)

Equivalent Linux BASH commands:


Simon Sheppard