How do I set a default app for an extension that is not listed?

Configure Windows File Association Pointers

  1. Open up an elevated [cmd.exe] command prompt as administrator
  2. Type in ASSOC .xml=xmlfile and press Enter

Further Resources

  • Windows Environment Variables

  • ASSOC /?

    Displays or modifies file extension associations
    ASSOC [.ext[=[fileType]]]
      .ext      Specifies the file extension to associate the file type with
      fileType  Specifies the file type to associate with the file extension
    Type ASSOC without parameters to display the current file associations.
    If ASSOC is invoked with just a file extension, it displays the current
    file association for that file extension.  Specify nothing for the file
    type and the command will delete the association for the file extension.
  • FTYPE /?

    Displays or modifies file types used in file extension associations
    FTYPE [fileType[=[openCommandString]]]
      fileType  Specifies the file type to examine or change
      openCommandString Specifies the open command to use when launching files
                        of this type.
    Type FTYPE without parameters to display the current file types that
    have open command strings defined.  FTYPE is invoked with just a file
    type, it displays the current open command string for that file type.
    Specify nothing for the open command string and the FTYPE command will
    delete the open command string for the file type.  Within an open
    command string %0 or %1 are substituted with the file name being
    launched through the assocation.  %* gets all the parameters and %2
    gets the 1st parameter, %3 the second, etc.  %~n gets all the remaining
    parameters starting with the nth parameter, where n may be between 2 and 9,
    inclusive.  For example:
        ASSOC .pl=PerlScript
        FTYPE PerlScript=perl.exe %1 %*
    would allow you to invoke a Perl script as follows:
    1 2 3
    If you want to eliminate the need to type the extensions, then do the
    and the script could be invoked as follows:
        script 1 2 3