UNERA33.DOC
                           November 20, 1988

       Notes by Irv Hoff, culled from earlier comments by others


                      RECOVERING ERASED CP/M FILES
                      ----------------------------
     UNERA, an utility program written by Gene Cotton, first appeared in
INTERFACE AGE for December 1981 (p. 96).

     When a file is erased, a hexadecimal "E5" is placed at the start of
that filename (the user-number byte) in the disk directory  area.   This
releases  the  blocks allocated to that file for future use by the BDOS.
If you should ever realize that you have inadvertently erased the  wrong
file, you can recover it immediately by using this program.

     Usage:

        A>UNERA FILENAME.EXT      (name of recently erased file)

     Since the BDOS usually proceeds sequentially through the blocks re-
maining on a disk during file allocation you can often recover an erased
file  even  after  some additional disk activity, particularly on a par-
tially used disk. Normally, by that time you would  have  forgotten  the
name of the file you wanted to recover, anyway.

     If you do recover a file immediately, it should be back to its nor-
mal  state.   If things have been added to the disk since you erased the
file, it may be recovered intact, or sections of it may have been  over-
written.  In that case, examine it carefully, and with luck it will turn
out to be normal.  In any case, portions of it can likely be recovered.

     If  a  file has been edited several times, each new edit often uses
different areas of the disk.  Recovery of such a file, even though  done
immediately, sometimes adds those previously used areas to the file just
erased.   Even  though  the resulting file is then longer than expected,
you can usually edit out the surplus.

     UNERA supports  "wildcards"  such as "?" or "*".  It  automatically
adjusts for the current CP/M 2.2 or for older CP/M 1.4.

     A description of the command format follows:

                    A>UNERA [d:]filename.typ [p]<CR>

where   d:            is the drive where the erased file is  located
                      (optional)

        filename.typ  is  the filename and type of the file that has
                      been erased; wildcards are permitted

        p             allows a change of diskettes and  prompts  for
                      hitting a <RETURN> to continue (useful on one-
                      drive systems)

     This  should  reclaim  to the current user area D:FILENAME.TYP that
you erased in error or otherwise wanted to recover.


COMMENTS:
---------

     Using ERAQ.COM or KILL.COM to erase files  rather  than  the  CCP's
built-in ERA command will minimize accidentally erasing incorrect files.
Those programs show the name(s) of the file(s) to be erased and then ask
you  to  verify  the operation on each file.  (They also work with wild-
cards.)

     Files may also be recovered by using  such  programs  as  DU,  DUU,
DUUP,  DUV8x,  etc.   These are very powerful multipurpose utilities for
disk handling; they require some talent to use and do not  compare  with
UNERA in simplicity.

     If  you  erase a file from within any user area and then run UNERA,
it will always restore the file to the current user area.  This can even
serve as a "quick and dirty" method of moving files between user areas.

     UNERA is written to run on an 8080, 8085, or Z80 microprocessor and
to be assembled with ASM.COM, the assembler that comes  with  CP/M.  The
program uses direct BIOS calls, to read and write back the directory.

                                                - Irv Hoff