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XXCOPY TECHNICAL BULLETIN #06


From:    Kan Yabumoto           tech@xxcopy.com
To:      XXCOPY user
Subject: File Attributes: what are they and how to use them.
Date:    2000-01-17
===============================================================================

Since XXCOPY has features which interact with the file attributes,
a discussion of XXCOPY cannot be complete without touching the basics
of the file attributes.  This article presents the fundamentals of
the file attributes and how XXCOPY manipulates them.  In addition,
some common techniques with the file attributes are discussed.


What are the file attributes?

  The operating systems (DOS, Win95/98, WinNT/2000/XP) maintain certain
  properties associated with every file and directories in addition to
  the file contents (data inside the file).  Such properties include

    file size in bytes
    file date/time (creation time, last-modify time, last-access time)
    file attributes
          archive bit   (shows that the file has not been archived yet)
          read-only bit (write-protect the file)
          directory bit (distinguishes a directory from a file)
          hidden bit    (hides from an ordinary directory listing)
          system bit    (denotes a system file whatever that means)

    These properties are mostly maintained by various components of
    the operating system and they are handled automatically.  So,
    the users may not be concerned with them.  However,  manipulating
    some of the properties are not very difficult and it can even be
    quite useful at times.  This article shows some common techniques
    associated with the file attributes.

    The file size is always determined by the actual size of the file
    and the only way to change it is to increase by appending more
    bytes to the existing file, or to decrease by overwriting with a
    shorter file.  The file date/time can be more easily changed.
    Since changing any of the three date/time values is supported by
    Win32 file I/O API, one can write a program to change them.  In fact,
    there are many utility programs available to do so.  Here, we will
    discuss the file attributes with greater details.


What is the file attributes?

    Although one can say the file size and the file date/time are file
    attributes (i.e., any properties associated with a file other than
    the file contents), with the more narrow definition and popular
    usage, the file attributes are collection of flags stored as a bit
    mapped 32-bit quantity which describes various aspects of the file.
    The original MS-DOS file attributes had only 8 bits in the file
    attributes, the Win32 file attributes are stored as a 32-bit quantity.

    Although the exact bit positions of the file attributes are not
    officially guaranteed to remain the same by Microsoft, they will
    probably never be changed.

       Bit 0     Read-Only
       Bit 1     Hidden
       Bit 2     System
       Bit 3     Volume Label
       Bit 4     Directory
       Bit 5     Archive

    Bit 3 (Volume Label) was used in MS-DOS to store the volume label
    just like an ordinary file in the directory.  Bit 4 (Directory)
    distinguish a file from a directory.  These two bits cannot be
    modified easily.  But, the remaining four bits (bit 0, 1, 2, and 5)
    can be examined and/or modified by the ATTRIB.EXE utility which is
    supplied by DOS/Windows.


The official Microsoft's way to manipulate the file attributes.

    Windows 95/98 provide a system utility program, ATTRIB.EXE which
    is usually stored in the C:\Windows\command\ directory.

    Here is the ATTRIB utility's command syntax

    ATTRIB [+R | -R] [+A | -A] [+S | -S] [+H | -H] filespec [/S]

       +   Sets an attribute.
       -   Clears an attribute.
       R   Read-only file attribute.
       A   Archive file attribute.
       S   System file attribute.
       H   Hidden file attribute.
       /S  Processes files in all directories in the specified path.

    For example if you want to clear the Archive attribute bit of all
    the files in a directory, execute the following command line.

       ATTRIB  -A c:\mydir\*


The Read-Only attribute.

    This bit is useful to make a file write-protected by software.
    For example, by setting the \AUTOEXEC.BAT file Read-only, you may
    protect the file from accidental deletion.  Or you may set a
    few files with the Read-only attributes and delete all the files
    using a "DEL *" (Delete all) command, the read only files will
    not be deleted under normal circumstances.  Certain files in the
    Win95/98 system are kept as Read-only by default (e.g., the system
    registry files).

    Before you can delete or overwrite a Read-only file, you must
    remove the Read-only file attribute bit.

    XXCOPY can force overwriting (or deletion) of a Read-only file by
    the /R switch.


The Hidden and System attribute.

    The purpose of the Hidden attribute bit is to make the file
    invisible in certain applications' file list display.  Since many
    file applications has the feature to ignore the Hidden attribute
    bit, the file with the Hidden attribute bit is not always invisible.

    The System attribute bit is probably the least rigorously
    defined in its usage.  From the early days of MS-DOS, the System
    attribute bit has been used in inconsistent manners that the bit
    seldom has much meaning.  The DIR command treat the System
    attribute similarly to the Hidden bit for directory listing.
    But, the COPY command does not care whether a file has the System
    attribute or not for copying it (Interestingly the DIR and COPY
    commands are both "built-in" commands which is implemented within
    the COMMAND.COM program).

    In most Win95/98 systems, you will find about twenty files in the
    root directory which are marked both Hidden and System.  These two
    attributes are often go hand in hand.  But, the choice seems
    quite arbitrary.

    While the usage of the Hidden and the System attribute bits are
    not well defined, the presence (or absence) of these attribute
    bits seldom change the actions of most system utilities except for
    the DIR and COPY commands, in most case, removing the Hidden and
    System attributes on most files do not cause any harm (except
    maybe some layer of protection from accidental erasure).

    XXCOPY by default (/H0) ignores a file with either Hidden or System
    attribute.  With the /H switch, you may include files with the
    Hidden or the System attributes in XXCOPY's copy action.


The Archive attribute.

    The Archive attribute was first introduced by MS-DOS version 2.0
    when the XCOPY utility was also created.  Therefore, the Archive
    attribute is probably best explained by how XCOPY handles the
    Archive attribute.  The purpose of the Archive attribute was clearly
    to quickly determine whether a file requires a back up (archiving).

    The Archive attribute is set whenever an existing file is either
    overwritten or modified (i.e., renamed or moved to another directory)
    by the file system.  A new file is usually created with the Archive
    attribute set.  The idea is to have a utility or application program
    to take the responsibility of clearing the Archive bit when a
    file is successfully backed up.  The next system backup operation
    will be made much more efficient by focusing only on the files with
    the Archive attribute bit set which are either newly created or
    modified in any way since all the Archive attributes are cleared the
    last time (i.e., the last backup time).


Incremental Backup using the Archive attribute.

    When XCOPY was the only "officially" designated system archive utility
    in MS-DOS, the Archive attribute had its usefulness.  Or, if only
    one backup regime in the system manipulates the Archive attribute bit
    and no other programs modifies the bit, the scheme works well.
    However, there are many backup and archive utilities that are
    capable of clearing the Archive attribute.

    Unfortunately, the operating systems do not enforce this
    "only-one-program-can-modify-the-Archive-bit" policy.  Because of
    possible interference with other applications which might clear the
    Archive attribute, we consider that the incremental backup scheme
    based upon the Archive attribute too risky to depend upon.

    Therefore, we do not recommend the use of the /M switch to perform
    any system backup operation.  For an incremental backup,  XXCOPY's
    /BI switch performs similar function with more confidence by
    comparing the files in the source and the destination with regard
    to the file size AND file date/time.  If either of the two does not
    match (or the file does not exist in the destination), the file will
    be copied.  This method is nearly as efficient as looking at the
    Archive bit.


Other usage of the Archive attribute.

    1.  You can determine which file(s) an application makes file
        changes (creation and modification) in a directory.  First,
        clear the Archive attribute of all the files in the given
        directory and run the application.  Then, check to see which
        files are marked by the Archive attribute.

        E.g.:  ATTRIB  -A c:\mydir\*       // clear the A bit first
               Run your application next
               XXCOPY  C:\mydir\*  /A/L    // list files with A bit set

    2.  Say, you have a directory with many files which you want to
        copy to a set of diskettes (one diskette cannot hold all of
        the files).  You can first set all the files with Archive
        attribute set first.  Then, run XXCOPY /M (or XCOPY /M).  The
        copy job will terminate as soon as the diskette becomes full.
        But the files which has already been copied are cleared of the
        Archive attribute.  So, run the same XXCOPY /M command again
        with a new diskette.  This time, the files which has been copied
        will be skipped.  Just repeat this operation until the files
        with Archive attribute run out.

        E.g.:  ATTRIB +A C:\mydir\*        // set the A bit set
               XXCOPY C:\mydir\*  A:\ /M   // copy files with A bit
               XXCOPY C:\mydir\*  A:\ /M   // repeat for next diskette
                 ...                       // continue until all files
                 ...                       // are copied.


Full Backup using the Archive attribute.

    We have stated that the use of the Archive attribute is not suitable
    for a reliable incremental backup.   However, once we abandon the
    notion that the Archive attribute serves as a persistent marker, it
    becomes even more useful.  Yes, the Archive bit as a temporary marker
    can be quite convenient.  The example in the preceding section of
    directory-copy to a set of diskette is a backup in a small scale.

    When you run Microsoft's ATTRIBUTE utility,

        ATTRIB  +A  C:\*  /S

    You will encounter the following messages:

        Not resetting hidden file C:\WINDOWS\...
        ...
        Sharing violation reading drive C
        Abort, Retry, Fail?

    In this case, entering "F" should let you continue.  But, apparently,
    the ATTRIB utility treats the "Fail" option as "Abort".  This is
    provably a bug in the Microsoft program.

    Our XXCOPY behaves more predictably.

        XXCOPY  C:\*  /S /AA

    The /AA and /AZ switches make XXCOPY to perform the same function
    similar to the ATTRIB utility does except it does a better job.
    XXCOPY's /AA switch sets (/AZ clears) the Archive attribute bit
    including the hidden files (it has automatically set the /H switch
    to include hidden files) and handles share-violation gracefully.
    If you need speed, you may suppress the console output by /Q or /Q2.

        XXCOPY  C:\*  /S /AA /Q    ;shows only the files which changes
        XXCOPY  C:\*  /S /AA /Q2   ;shows only statistics at the end

    After setting the Archive attribute bit of all the files in the
    volume, you can start repeated backup using the /M switch

        XXCOPY  C:\*  T:\mybackup   /S /M /H ...

        (change the target media when it is full and try again)

    You may apply the same basic technique to a full-scale volume backup
    using the Archive attribute.  This is quite useful when you are
    backing up a large volume into smaller removable medium
    (e.g., CD-R, CD-RW, Tape-based file system, or even floppy disk).

    If you have an AutoLoader tape drive (e.g., HP SureStore 12000),
    a working batch file example based on this scheme is available at
    http://www.datman.com/tbul/dmtb_038.htm.


List of XXCOPY's file attributes related switches.

    Archive bit

     /A0   Cancels *ALL* /A, /M, /AT, and /AX switches.
     /A    Excludes files without Archive bit set
     /AC   Ignores the Archive bit (always clears Archive bit)
     /M    Excludes files without Archive bit set (clears Archive bit)
     /AA   Sets   the src file archive bit (without actually copying)
     /AZ   Clears the src file archive bit (without actually copying)
           Note: Both /AA and /AZ implicitly set /H (can be overridden)

    Hidden and System bit

     /H0   Excludes files with Hidden or System Attributes bits (default)
     /Ho   Excludes files without Hidden or System Attributes bits.
     /H    Ignores the Hidden or System Attributes bits

    Destination Read Only bit

     /R0   Excludes a file when it exists in dst as read-only (default)
     /R    Allows overwrite/delete of a read-only file if necessary

    Destination file attributes

     /K0   Keeps H-bit and S-bit, sets A-bit, clears R-bit (default).
     /KS   Keeps the source attributes including the read-only bit.
     /KD   Keeps the attributes of destination (overwritten) file
     /KN   Sets the destination attributes to normal (only the A-bit)



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