Function 5Ah (90)        Create Unique File                         ≥ DOS 3.0

    Creates a unique filename, then opens that file in the specified
    directory.

       On entry:      AH         5Ah
                      CX         File attribute
                      DS:DX      Pointer to path ending in \ (ASCIIZ string)

       Returns:       DS:DX      Pointer to filename (ASCIIZ string)
                      AX         Error code, if CF is set

       Error codes:   3          Path not found
                      5          Access denied

                      Call Function 59h for extended error code information.

       Network:       Requires Create access rights

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    Function 5Ah creates a file, and opens it in compatibility mode with
    Read/Write access. This function is often used to create temporary
    files, but note that DOS does not automatically delete the file when
    the program terminates.

       Notes:         The pathname must end with a backslash character.

                      Reserve 13 bytes following the pathname so that DOS
                      can append name of the newly created file.