ASSOCIATE (Available in Windows Resource Kit)

One step file association.
Associate utility combines the ASSOC and FTYPE commands. ASSOCIATE assigns an extension directly with an executable application and stored FileType to the system registry.

ASSOCIATE .ext filename [/q /d /f]


.ext Extension to be associated.
filename Executable program to associate .ext with.
/q Quiet – Suppress interactive prompts.
/f Force – Force overwrite or delete without questions.
/d Delete – Delete the association.
/U  Display or set the association in HKCU\Software\Classes

A file extension is the last few characters in a FileName after the period. 

So a file called xyz.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.

Example: adding a File Association

To add the File Type “abcFile”=Notepad.exe and also set the File Association of .abc=”abcFile” run this command:

ASSOCIATE .abc Notepad.exe

Example: Removing a File Association


Note that /d will delete the File Association but will NOT delete the File Type.

File types created by Associate.exe are always given a name in the form xxxfile, where xxx is the file extension.