CU.ASM

	CU.ASM is a program to move files from one user number to 
another.   It  is  from an idea by Aubrey Hutchinson  of  Pompano 
Beach,  Florida published in Dr.  Dobbs Journal, March 1983 (page 
82).

OPERATION:       CU [dr:]FILENAME.TYPE s,d [/N]

Where dr: is the drive designator (optional),
        s is the source user number, and
        d is the destination user number.
        N means don't ask before each change

Filename.typ may be ambiguous, same as with the ERA command. 

EXAMPLE:

                 CU *.ASM 0,3 /N

This  would transfer all files of type ASM from user 0 to user  3 
without asking before each change.

R/O and SYS files can be moved.   R/O files will be R/W after the 
move.

CAUTION:  If a file already exists in the destination user  area, 
it  is possible with this program to create another one with  the 
same name.  Using the ERA command will then erase BOTH of them.

VIDEO ATTRIBUTES:

	The  distributed  version  of  the  program uses no video
attributes.  To take advantage of clear screen and reverse video,
place the required attribute strings in the video attribute  area
of the ASM file and reassemble.

THEORY OF OPERATION:

        
        The  first  byte  of  each  file  specification  in   the 
directory is the user designation.  CP/M sets this byte to E5 hex 
when a file is erased.  This program finds the location of the E5 
in  the BDOS and changes it to the desired user  number.   CP/M's 
file  erase function is then called,  causing this user number to 
be written to the directory.

        The  method used to find the E5 byte is to get  the  warm 
boot  address  at locations 1 and 2 and subtract 654H  bytes  and 
then  to check that E5 is at the resulting addrress.   This finds 
the correct byte on my system except when running under a progran 
such as QK20 which changes the warm boot address.  In such a case 
the program then searches through memory looking for:

        MVI    M,E5H
        MVI    C,xx

        I  am  hopeful  that this method will work on  most  CP/M 
systems,  but I have only tested it on my own CP/M 2.2, and if it 
doesn't  work  on  another system the program would  have  to  be 
modified.

	Comments, corrections, etc. welcomed.

Submitted by:

Robert Wilcox
920 N. Washington
Owosso, MI  48867