arc521.doc

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    ARC l junk *.doc


ARC prints a short listing of an archive's contents
like this:

    Name          Length    Date
    ============  ========  =========
    ALPHA.TXT         6784  16 May 85
    BRAVO.TXT         2432  16 May 85
    COCO.TXT           256  16 May 85
            ====  ========
    Total      3      9472


"Name" is simply the name of the file.






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"Length" is the unpacked file length.  In other words,
it is the number of bytes of disk space which the file
would take up if it were extracted.

"Date" is the date on which the file had last been
modified, as of the time when it was added to the
archive.

"Total" is pretty obvious, I think.


ARC prints a verbose listing of an archive's contents
like this:

Name          Length    Stowage    SF   Size now  Date       Time    CRC
============  ========  ========  ====  ========  =========  ======  ====
ALPHA.TXT         6784  Crunched   35%      4413  16 May 85  11:53a  8708
BRAVO.TXT         2432  Crunched   41%      1438  16 May 85  11:53a  5BD6
COCO.TXT           256   Packed     5%       244  16 May 85  11:53a  3AFB
        ====  ========            ====  ========
Total      3      9472             27%      6095


"Name", "Length", and "Date" are the same as for a
short listing.

"Stowage" is the compression method used.  The
following compression methods are currently known:

       --          No compression.

     Packed        Runs of repeated byte values are
                   collapsed.

    Crunched       Lempel-Zev compression technique
                   employed.

    Squeezed       Huffman encoding compression
                   technique, as employed by an
                   earlier version of ARC.

"SF" is the stowage factor.  In other words, it is the
percentage of the file length which was saved by
compression.  The total stowage factor is the stowage
factor for the archive as a whole, not counting
archive overhead.

"Size now" is the number of bytes the file is
occupying while in the archive.





ARC                                              Page 9
"Time" is the time of last modification, and is
associated with the date of last modification.

"CRC" is the CRC check value which has been stored
with the file.  Another CRC value will be calculated
when the file is extracted or tested to ensure data
integrity.  There is no especially good reason for
displaying this value.



RUNNING FILES

Archive entries may be run without being extracted by
use of the "R" (Run) command.  For example, if you had
an archive named "JUNK.ARC" which contained a file
named "LEMON.COM", which you wished to run, you could
type:

    ARC r junk lemon

You can run any file from an archive which has an
extension of ".COM", ".EXE", ".BAT", or ".BAS".  You
do not have to specify the extension, but all matching
files are run if you do not.  In other words, if you
had an archive named "JUNK.ARC" which contained the
files "LEMON.COM", "LEMON.EXE", and "LEMON.BAS", and
you typed:

    ARC r junk lemon

Then all three programs will be run.  You can avoid
this by specifying an extension in this case.

You can give arguments to the program you are running
by appending them to the command line.  For example,
if you have an archive named "JUNK.ARC" which contains
a program named "LEMON.COM", and you wanted to run it
giving it the argument "JUICE", you would type:

    ARC r junk lemon juice

You will need a fair amount of memory to run a program
from an archive.  It probably cannot be done with less
than 256k.









ARC                                             Page 10
In practice, the file to be run is extracted, run, and
then deleted.  In other words, the above example is
equivalent to:

    ARC x junk lemon.com
    lemon juice
    erase lemon.com

If you have an archive which contains a program that
you will be running often, then you should probably
extract the program from the archive and use it
normally.



PRINTING FILES

Archive entries may be examined with the "P" (Print)
command.  This works the same as the Extract command,
except that the files are not created on disk.
Instead, the contents of the files are written to
standard output.  For example, if you wanted to see
the contents of every ".TXT" file in an archive named
"JUNK.ARC", but didn't want them saved on disk, you
could type:

    ARC p junk *.txt

If you wanted them to be printed on your printer
instead of on your screen, you could type:

    ARC p junk *.txt >prn



TESTING AN ARCHIVE

The integrity of an archive may be tested by use of
the "T" (Test) command.  This checks to make sure that
all of the file headers are properly placed, and that
all of the files are in good shape.

This can be very useful for critical archives, where
data integrity must be assured.  When an archive is
tested, all of the entries in the archive are unpacked
(without saving them anywhere) so that a CRC check
value may be calculated and compared with the recorded
CRC value.






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For example, if you just received an archive named
"JUNK.ARC" over a phone line, and you want to make
sure that you received it properly, you could type:

    ARC t junk

It defeats the purpose of the T command to combine it
with N or W.



CONVERTING AN ARCHIVE

The "C" (Convert) command is used to convert an
archive entry to take advantage of newer compression
techniques.  This is occasionally desirable when a new
version of ARC is released.  Please refer to the
revision history section for details on when new
compression methods were implemented.

For example, if you had an archive named "JUNK.ARC",
and you wanted to make sure that all files with an
extension of ".DOC" were encoded using the very latest
methods, you could type:

    ARC c junk *.doc

Or if you wanted to convert every file in the archive,
you could type:

    ARC c junk























ARC                                             Page 12
          ARC OPTIONS



This section describes the options which are available
to modify how ARC works.  Any of these options can be
combined with any of the commands, though the result
may not always be something you'd want to do.



SUPPRESSING COMPRESSION

The "S" (Suppress compression) option can be combined
with any command that updates archive entries.  These
include Add, Move, Update, Freshen, and Convert.  The
effect of the S option is to prevent any compression
techniques from being employed.  This is intended to
allow you to add a few files at a time to an archive
quickly, and then later convert the archive to
compress everything at once.

For example, over the course of a day you might give
each of the following commands:

    ARC as junk *.txt
    ARC as junk *.mac
    ARC as junk *.doc

At the end of the day, when you have finished adding
things to the archive, you could have all of the
archive entries compressed at once by typing:

    ARC c junk

You could also decompress the archive by typing:

    ARC cs junk

though I can't imagine why you'd want to.














ARC                                             Page 13
BACKUP RETENTION

When ARC changes an archive (during an Add, Move,
Update, Freshen, Delete, or Convert) it creates a new
archive with the same name, but with an extension of
".$$$".  For example, if you add a file to an archive
named STUFF.ARC, then ARC will create a new archive
named STUFF.$$$.  ARC will read from your existing
archive and write out the new archive with any changes
to the ".$$$" copy.

Normally when ARC is finished it deletes the original
and renames the new archive to the original name (ie.
STUFF.ARC goes away, and STUFF.$$$ becomes the new
STUFF.ARC).  Among other things, this means that if
anything goes wrong and ARC is unable to finish, then
your original archive will still be intact.


In some circumstances you may wish to retain the
original version of the archive as a backup copy.  You
can do this easily by using the Backup option.  Add
the letter "B" to your command, and ARC will rename
your original archive to have an extension of ".BAK"
instead of deleting it.


In other words, if you wanted to add "WASTE.TXT" to an
archive named "JUNK.ARC", but wanted to keep a backup
copy, then you would type:

    ARC ab junk waste.txt

Your original archive would become "JUNK.BAK", while
"JUNK.ARC" would contain the new "WASTE.TXT" file.


If you keep a backup of an archive which already has a
backup, then the older backup copy is deleted.















ARC                                             Page 14
MESSAGE SUPPRESSION

ARC prints three types of messages: warnings,
comments, and errors.

Warnings are messages about suspected error
conditions, such as when a file to be extracted
already exists, or when an extracted file fails the
CRC error check.  Warnings may be suppressed by use of
the "W" (Warn) command.  You should use this command
sparingly.  In fact, you should probably not use this
command at all.

Comments (or notes) are informative messages, such as
naming each file as it is added to the archive.
Comments and notes may be suppressed by use of the "N"
(Note) command.

Errors are actual system problems, such as running out
of disk space.  You cannot suppress errors.


For example, suppose you extracted all files with an
extension of ".BAS" from an archive named "JUNK.ARC"
Then, after making some changes which you decide not
to keep, you decide that you want to extract them all
again, but you don't want to be asked to confirm every
one.  In this case, you could type:

    ARC xw junk *.bas

Or, if you are going to add a hundred files with an
extension of ".MSG" to an archive named "TRASH.ARC",
and you don't want ARC to list them as it adds them,
you could type:

    ARC an trash *.msg

Or, if you want to extract the entire contents of an
archive named "JUNK.ARC", and you don't want to hear
anything, then type:

    ARC xnw junk


A special case is provided when extracting files from
an archive.  One of the various warnings that can
occur is when a file being extracted already exists on
disk.  Normally, ARC will stop and ask you if you want
to overwrite the file.  This can be suppressed with
the "W" command, but that will also suppress any



ARC                                             Page 15
warnings about other things, like failed CRC checks
and such.

The "O" (Overwrite) option suppresses *only* the warning
that the file already exists.  For example, in our
earlier case of extracting all the ".BAS" files from
"JUNK.ARC", a much safer way to do it is to type:

    ARC xo junk *.BAS













































ARC                                             Page 16
ENCRYPTION/DECRYPTION

Archive entries may be encrypted and decrypted by
using the "G" (Garble) option.  The Garble option
takes the remainder of the command string as the
password to use, so it must be the *last* option.


For example, if you wanted to add a file named
"WASTE.TXT" to an archive named "JUNK.ARC", and you
wanted to encrypt it using the password "DEBRIS", then
you would type:

    ARC agdebris junk waste.txt

Later on, when you want to extract it again, you would
type:

    ARC xgdebris junk waste.txt

The password you supply is used to encrypt (or
decrypt) the archive entry by performing an exclusive
OR between each byte of the packed data and each byte
of the password.  The password can be any length, and
each of its bytes is used in rotation.  The password
is converted to uppercase before it is used, so it is
*not* case sensitive.  Since the encryption is performed
on the packed data, it has no effect on stowage
factors.

This is not a particularly sophisticated means of
encryption, and it is theoretically possible to crack.
Still, since it is performed on the packed data, the
result should be quite sufficient for casual use.


You can, if you wish, use different passwords for
different files in an archive, but we advise against
it.  If you are going to encrypt an archive, we
suggest you use the same password for every file, and
give the password whenever you do anything at all with
the archive.  It is possible to list the entries in an
encrypted archive using the "L" and "V" commands
without giving the password, but nothing else will
work properly.


We advise that you use this option sparingly, if at
all.  If you should forget or mistype your password,
it is highly unlikely that you will ever recover your
data.



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        RAMDISK SUPPORT



If you have a RAMdisk, or other high-speed storage,
then you can speed up ARC somewhat by telling it to
put its temporary files on the RAMdisk.  You do this