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User's Manual for the ARJ archiver program, December 1990
ARJ software and manual copyright (c) 1990 by Robert K Jung.
All rights reserved.
ARJ version 0.20 BETA test release
***IMPORTANT NEWS*****************************************************
Previous users of ARJ should read the WHATSNEW.DOC!!! It contains
important information about changes and issues since test releases
0.13a, 0.14, 0.15, and 0.15a.
**********************************************************************
INTRODUCTION:
ARJ is my first attempt to use my interest in compression
technology to produce an archiver for personal use on my PC and on
minicomputers. ARJ is written entirely in ANSI C and only uses ANSI
standard libraries. All machine dependent functions (file
date-time modified, file attributes, etc.) are contained in a
single environment source file using ifdefs to enable one to
maintain a single version of the source code for multiple different
machines. This version has manually optimized CRC and output
routines.
The current functionality of ARJ is patterned after that of LHARC
with additional features derived from those of the competition.
I have created a new archive format for ARJ to support cross
platform archives, multiple volume archives, and a new security
envelope feature. Trying to maintain compatibility with existing
formats is difficult and possibly expensive (legally speaking).
In addition, there are definite plans to port full blown versions
of ARJ to the AMIGA and ATARI ST platforms. I expect those
versions to be available before mid-1991. There will be a
simplified version of ARJ in source code to be released for the
UNIX platform late in 1991.
This may start another compression war, but competition begets new
and better standards. Just look at the improvements to PKZIP over
the past few years. ARJ is the result of my desire for an archiver
that would do what I needed. It is not an attempt to be everything
to everyone. But if ARJ is what you need, so much the better. I
intend to keep improving ARJ over the long haul even after LHARC
2.0 is released, because data compression is my hobby.
Some users, however, believe that miracles will be the result of
such a war. I have included a brief synopsis of the state of the
art of data compression research at the end of this document. This
may be enlightening to archiver users. Archivers have just caught
up with the state of the art.
TERMINOLOGY:
The following terms are used through this manual.
ARCHIVE - This is a file containing one or more files which may
be compressed and containing file related information such as
filename and date-time last modified, etc.
ARJ FILE - This is an archive created by ARJ.
COMPRESSION - The process of encoding redundant information into
data requiring less storage space.
COMPRESSION PERCENTAGE/RATIO - The percentage compression reported
by ARJ is a variation of one of the TWO standard methods of
expressing compression ratio in the technical literature. ARJ uses
the compressed size / original size ratio. The other method is the
inverse ratio. When ARJ reports 96% as the compression ratio, that
means that the compressed file is 96 percent of the original size
(very little compression). Other archivers use their own methods.
LHARC uses the same ratio as ARJ.
EXTRACTION or UNCOMPRESSION - The processing of recreating the
exact information that was previously compressed.
SELF-EXTRACTION MODULE - This is an archive that is an
executable file that is capable of extracting self-contained
files.
TEXT MODE - In text mode, ARJ inputs the file using the C library
text mode which translates the carriage return, linefeed control
characters of MS-DOS to a single linefeed character. This saves
space and provides the option for cross platform file extraction.
On another platform, the host C library would change the single
linefeed to the host text newline separator sequence. In addition,
for platforms, such as PRIMOS which set bit 8 in ASCII text
characters, ARJ sets/resets bit 8 according to the platform
extracted to.
VOLUMES - These are ARJ archives that are in sequence and have
been created by a single ARJ command. Files in the volumes may
span volumes in a split format.
MAJOR FEATURES OF ARJ:
BEST compression in terms of size reduction of the currently
available archivers including PKZIP 1.10, PAK 2.51, and LHARC
1.13c. Users have reported that ARJ also compresses slightly
better than ARC 7.00 BETA. ARJ is particularly effective with
database file, text files, and very small files.
Archive and individual file comments with option of inputting
comments from a file.
32 bit CRC file integrity check.
Test new archive before overwriting the original archive option.
Multiple volume archives with one ARJ command. This allows the
user to backup a full hard disk drive to multiple floppies.
Recovery of individual files is convenient because each volume is
an individual archive. No need to use SLICE with ARJ.
Multiple string searching within archive files.
Built-in facility to recover files from broken archives.
Self-extraction feature that is internal to the ARJ runfile. The
SFX module is full-featured with a built-in help screen.
Internal string data integrity check in ARJ to resist hacking a la
LHARC to ICE.
Archive security envelope feature to resist tampering with secured
archives. This feature disallows ANY changes to a secured archive.
Not even comments can be changed.
Password option to encrypt archived files.
Text mode data compression option to enable movement of text files
from one host machine to another. Text mode also results in
greater file size reduction on MS-DOS machines.
File extraction to screen in a paged mode to permit browsing
through an archive.
Specification of the files to be added to an archive via one or
more list files. In addition, ARJ can generate a list file.
Specification of files to be excluded from processing by ARJ.
Sub-directory recursion during compression and extraction.
ARJ source code compilable on any machine supporting ANSI C. This
code has compiled and produced working archivers on at least two
platforms. This will allow the porting of ARJ to many other
platforms. Source code is not currently available for public
release. However, I do intend to release source code for a UNIX
version of ARJ in 1991.
BETA TEST RELEASE NOTES:
This version is provided for your personal use for evaluation. I
would appreciate bug reports, comments, and suggestions. This is
your opportunity to improve this archiver. In any case, the ARJ
1.00 production release WILL maintain compatibility with version
0.20, so that your investment in time and files in ARJ will not be
obsoleted.
This version does NOT include any expiration feature. ARJ 0.20 is
fully functional. No function has been crippled. But this is a
BETA version. You should fully test any archives that you plan to
permanently keep in ARJ format. I suggest using the "-jt" test
archive switch to test all archives that you build.
Your first comment after using ARJ probably may be that it is
somwhat slow during compression. But if you value file size
reduction more than time, then ARJ may be for you. In any case,
archive extraction speed is comparable to other archivers. You may
also like the speed and compression of methods 3 and 4 (-m3,-m4).
Here is a suggested command that will test ARJ on all of your files:
arj a A:\vol c:\*.* -r -jt -y "-vasdel A:\vol.*"
I am especially interested in your comments on the following
features of ARJ:
Archive by date-time stamp with the "-o" switch.
The use of .A01, .A02, etc for multiple volume archives.
The new "-jv" verbose switch option for the "l" and "v" commands.
GETTING STARTED:
I assume that you have a copy of the self-extracting ARJ module
named ARJ020.EXE. Typing ARJ020 [RETURN] at the DOS command prompt
will initiate the self-extraction feature. ARJ020 will by default
extract its files to the current directory. When ARJ020 starts,
you will see several lines of text describing ARJ and then a line
asking if you wish to continue extraction. Entering "yes" or "y"
will continue the extraction. If there are any duplicate filenames
in the current directory, the program will prompt you for
overwriting. You can say "yes", "no", or "quit". Only the
extracted ARJ.EXE file needs to be copied to a directory named in
your "PATH" command in your autoexec.bat file. On many PCs, this
directory may be C:\DOS or C:\BIN. With MS-DOS 3.0 and above,
you can use path notation "\BIN\ARJ e archive" to use ARJ.
You may, of course, prefer to use ARJ 0.15 to extract the contents
of ARJ020.EXE file manually. Example: ARJ e arj020.exe \temp\
The AV.EXE file is only a ARJ file lister provided as a skeleton
program for software developers. It is not needed to use ARJ.
QUICK START TO USING ARJ:
To create an ARJ archive containing all of the files in the
current directory:
ARJ a archive
To create an ARJ archive containing all files with the ".DOC"
extension in the current directory:
ARJ a archive *.DOC
To create an ARJ archive containing all of the files in the
named directory and all files in subdirectories of the named
directory:
ARJ a archive named_directory\*.* -r
To extract all of the files in an archive to the current
directory:
ARJ e archive
To extract all of the files in an archive to a named directory:
ARJ e archive named_directory\
To extract all files with the ".DOC" extension to the current
directory:
ARJ e archive *.DOC
To extract all of the files in an archive recreating the
original directory structure:
ARJ x archive original_directory_name\
To list all of the files in an archive:
ARJ l archive
HOW TO USE ARJ:
Where I do not elaborate in this manual, you can assume that ARJ
usage is similar to that of LHARC.
If you type ARJ [return] you will see a help screen similar to the
following:
ARJ 0.20 BETA Copyright (c) 1990 Robert K Jung
All rights reserved. Free for non-commercial personal use. Dec 27 1990
List of frequently used commands and switches. Type ARJ -? for more help.
Usage: ARJ <command> [-<sw> [-<sw>...]] <archive_name> [<file_names>...]
Examples: ARJ a -r -wtemp software , ARJ l software , ARJ e software readme
<Commands>
a: Add files to archive m: Move files to archive
d: Delete files from archive t: Test integrity of archive
e: Extract files from archive u: Update files to archive
f: Freshen files in archive v: Verbosely list contents of archive
l: List contents of archive x: eXtract files with full pathname
<Switches>
c: (All) skip time-stamp Check n: (All) only New files (not exist)
d: (afu) with Delete (move) r: (All) Recurse subdirectories
e: (afu) Exclude paths from names u: (All) Update files (new and newer)
f: (All) Freshen existing files v: (All) enable multiple Volumes
g: (All) Garble with password w: (Upd) assign Work directory
i: (All) with no progress Indicator x: (All) eXclude selected files
m: (afu) with Method 0, 1, 2, 3, 4 y: (All) assume Yes on all queries
If you type ARJ -? [return] you will see a more detailed help
screen similar to the following with page pauses. Type ARJ -? -jp
to toggle the pauses off.
ARJ 0.20 BETA Copyright (c) 1990 Robert K Jung
Usage: ARJ <command> [{/|-}<switch>[-|+|<option>]...] <archive_name>[.ARJ]
[<base_directory_name>\] [<!list_name>|<path_name>|<wild_name>...]
<Commands>
a: Add files to archive p: Print files to standard output
c: Comment archive files r: Remove paths from filenames
d: Delete files from archive s: Sample files to screen with pause
e: Extract files from archive t: Test integrity of archive
f: Freshen files in archive u: Update files to archive
l: List contents of archive v: Verbosely list contents of archive
m: Move files to archive w: Where are text strings in archive
n: reName files in archive x: eXtract files with full pathname
<Switches>
a: (afu) allow any file Attribute v: (All) enable multiple Volumes
b: (afu) Backup changed files vv: beep before successive volumes
b1: (afu) Backup + reset archive bits va: auto-detect space available
c: (All) skip time-stamp Check vas: auto-detect and system command
d: (afu) with Delete (move) vvas: beep, auto-detect, and command
asks permission before deleting vascommand: -va + execute command
e: (afu) Exclude paths from names v181000: create 180K size archives
e1: (afu) Exclude base dir from names v360s: 362K size and system command
f: (All) Freshen existing files v360, v720, v1200, v1440: abbrevs
g: (All) Garble with password vv360s: beep, 362K size and command
gstew: garble with password stew w: (Upd) assign Work directory
i: (All) with no progress Indicator wtmp: use tmp as work directory
k: (Upd) Keep archive file backup x: (All) eXclude selected files
l: (All) create List_name file x*.exe: exclude *.exe files
lnames.lst: creates names.lst x!nam.lst: exclude files in nam.lst
m: (afu) with Method 0, 1, 2, 3, 4 multiple exclusions are allowed
m0: store (no compression) y: (All) assume Yes on all queries
m1: maximum compression use this switch for batch mode
m2: less memory and compression ja: (All) show ANSI comments
m3: FAST! less compression jc: (All) test for Console RAW mode
m4: FASTEST! least compression je: (Upd) create self-Extracting archive
n: (All) only New files (not exist) jf: (afu) store Full specified path
o: (All) On or after YYMMDDHHMMSS jk: (Upd) Keep temp archive on error
o901225: on/after 12/25/90 jp: (lv) Pause after each screenful
ob: (All) Before YYMMDDHHMMSS jr: (All) Recover broken archive files
ob901225: before 12/25/90 js: (afu) Store archives by suffix
p: (All) match using full Pathnames default is arj, arc, lzh, pak, zip
q: (All) Query on each file js.zoo.lzh: store .zoo, .lzh files
r: (All) Recurse subdirectories jt: (Upd) Test temporary archive
s: (Upd) set archive time-Stamp ju: (All) translate UNIX style paths
t: (afu) archive file in Text mode jv: (All) set Verbose display
t0: force binary mode jx: (afu) start at eXtended position
u: (All) Update files (new + newer) jx10000: start at position 10000
Simple examples:
Archive all files in current directory: arj a archive
Extract archive to current directory: arj e archive
Extract new and newer files without query: arj e archive -u -y
List contents of archive: arj l archive
Other examples:
arj a -wd:\ /t /m2 /s archive.arj c:\source\ *.c *.h
arj a floppy software\*.* product\*.* /lnames.lst /r /v360000
arj e archive \temp\ *.c *.h read.me -u -y
ARJ 0.20 - Archiver - Copyright (c) 1990 Robert K Jung. All rights reserved.
ARJ is free to use, copy, and distribute for non-commercial personal use if
ARJ is not modified and no fee is charged for using, copying, or distributing
ARJ except as noted in the license document. If you find ARJ of value, a gift
of 10 dollars or any amount would be greatly appreciated. For more
information concerning ARJ, see the accompanying documentation or contact:
Robert K Jung CompuServe userid: 72077,445
2606 Village Road West Internet address: 72077.445@compuserve.com
Norwood, Massachusetts 02062
USA
ARJ LIMITATIONS:
ARJ will accept up to: 64 filenames/wildnames on command line
16000 filenames resulting from wildnames
8000 filenames/wildnames to exclude
8000 ARJ filenames resulting from wildnames
2048 character comments
(up to 25 lines or 1 file)
ARJ requires approximately 300,000 bytes plus the memory necessary
to store all of the pathnames to be archived.
As far as I know there is no limitation on the number of files that
can be stored in one archive. However, each add command can only
add a maximum of 16000 files at a time depending upon memory
availability. I expect that a normal maximum of 5000 to 8000
filenames can be handled without running out of memory during the
compress phase.
If you do not have enough memory, you should use the "-l" switch to
dump the filenames to a list file. You can then break the list
file into smaller files and use multiple ARJ commands to archive
all of the files.
Example:
ARJ a archive \*.* -r -lname.lst
If the above command fails due to lack of memory, split the
name.lst file into smaller pieces named name1.lst, name2.lst,
etc. Then execute:
ARJ a archive !name1.lst
ARJ a archive !name2.lst
.
.
ARJ currently does NOT differentiate between wildnames like "C:*.*"
and "C:\*.*". ARJ would expand each of those two wildnames into a
list twice that could be up to twice as long as necessary.
When updating an archive, ARJ creates a temporary file named
ARJ.$$$ in the current directory or work directory.
While ARJ is scanning a wildcard filespec, ARJ will change the name
of the target archive to ARJ.$$$ while the scan is proceeding to
avoid including the archive itself in an add command. Also, as a
result, you cannot add a file named ARJ.$$$ to an ARJ archive.
DIFFERENCES BETWEEN ARJ AND LHARC:
The archive formats are NOT compatible.
The compression and decompression algorithms are NOT compatible.
ARJ only supports its own archive format.
ARJ by default stores the full specified pathname of files
archived minus any drive letter and root symbol.
The "e" and "x" commands will by default extract all of the files
in the archive without using date time stamps to select files. You
should specify "-u -y" to duplicate LHARC functionality.
The ARJ archive suffix is ".ARJ".
ARJ does NOT sort filenames when archiving.
IMPORTANT NOTES:
When using the "-w" working directory switch, ARJ does not check on
space availability before overwriting the original archive if it
exists. Be sure that you have enough disk space for the new
archive before using the "-w" switch. If ARJ aborts in this
situation because of disk space, ARJ will keep the temporary
archive.
By default, ARJ does not see hidden or system files when using
wildnames. ARJ will process system and hidden when you either
specify the exact filename or specify the "-a" switch.
For MS-DOS environments that switch on RAW console mode via
programs like RAW.COM, ARJ has a new switch "-jc" which tells ARJ
to check for RAW mode and switch its STDIN from fgets() to cgets().
If this switch is not used, ARJ will hang up on its first user
prompt.
Like LHARC and PKZIP, ARJ requires extra disk space to UPDATE an
archive file. ARJ will backup the original archive while it
creates the new archive, so enough room must be available for both
archives at the same time.
Currently, ARJ will not extract to a readonly file.
ARJ ERROR SITUATIONS:
ADD:
If a user specified file is not found during an add, ARJ will
continue processing, but will keep the archive and terminate with
an error condition.
In a disk full condition or any other file i/o error, ARJ will
promptly terminate with an error condition and delete the temporary
archive file unless the user has specified the "-jk" switch.
MOVE:
ARJ will only delete files that have been successfully added to the
archive. If you have specified the "-jt" (test) switch, ARJ will
abort on any error including the file not found during add. If you
specify the "-jk" switch, ARJ will not delete the temporary archive
upon an abort.
EXTRACT:
In a disk full condition or any other file i/o error, ARJ will
promptly terminate with an error condition and delete the current
output file.
ARJ USER ACTION PROMPTS:
ARJ prompts the user for action at certain times. There are
several types of prompts. One is for yes/no permission, another is
for a new filename, another is for archive comments, and one other
is for search strings. The yes/no prompts will also accept "quit"
for program termination and "always" to bypass further user
prompts.
Since ARJ uses STDIN for user input, be careful about typing ahead
anticipating prompts. ARJ may prompt you for an unexpected action
and use your earlier input.
ARJ ENVIRONMENT VARIABLE:
ARJ will first look for an environment variable named ARJ_SW and
use its value as switch options for ARJ. If ARJ finds such an
environment variable, it will display a message to that effect.
Type SET ARJ_SW = <switches>
Example: SET ARJ_SW = -w\temp -k -e
As in LHARC, command line switches can be selected to override
ARJ_SW settings.
ARJ COMMAND LINE SYNTAX:
ARJ <command> [-<switch>[-|+|<option>]...] <archive_name>[.ARJ]
[<base_directory_name>\] [<!list_name>|<path_name>|<wild_name>...]
Currently commands and switches can be entered in upper or lower
case. That is subject to change. For compatibility with future
versions, you should use lower case commands and switches.
ARJ now supports the use of either "-" or "/" as the switch option
character. The first occurrence of either "-" or "/" that ARJ
encounters will determine the switch symbol. You may NOT mix and
match switch symbols. This also includes the ARJ_SW environment
variable. ARJ_SW is checked first for switches. Throughout this
document, the symbol "/" may be substituted for "-" in switch
usage.
Examples: ARJ a A:archive *.* /va /r is correct
ARJ a A:archive *.* /va -r IS INCORRECT USAGE!
Switch options SHOULD NOT be combined. At this time combinations
such as "-ki" representing "-k" and "-i" will work, but may not in
the future.
The switch option "--" tells ARJ that there are no more switch
options to process in the current command line. This is useful
when you need to enter filenames beginning with "-".
Example: ARJ a archive -- -testfile
The standard ARJ file suffix is ".ARJ". Subsequent multiple volume
archives end in ".A01", ".A02", etc.
The ARJ command must be the first non-switch argument after "ARJ".
The ARJ archive name must be the first filename on the command
line. The base directory, if any, must be the second filename
argument. The switches and other filenames can be in any order.
The base directory name must end with "\" (backslash) or ":"
(colon).
For commands other than adding files to an archive (a, f, m, u),
you can specify a wildcard for the archive name such as "*.ARJ".
Also, if you also specify the "-r" switch, ARJ will search
sub-directories for ARJ archives (*.ARJ) also. Be careful using
wildcards this way. The command ARJ d *.ARJ -r will delete every
file in every archive in and under the current directory.
Example: ARJ l * -r will list all of your *.ARJ files.
Switches specified on the command line will either toggle or
override switches specified with the ARJ_SW environment variable.
Switch usage is identical to that of LHARC.
"-s+" turns on switch "s".
"-s-" turns off switch "s".
"-s" toggles the state of switch "s".
"-sname" provides the name argument for switch "-s".
"--" skip processing of any more switch options.
Wild_names follow MS-DOS convention. "*.*" means all files.
"*.DOC" means all files with an extension of ".DOC". "?B*.*"
means all files with a second character of "B".
The default for <wild_name> for all commands except for "d" is
"*.*".
Filename matching in the archive does not use full pathnames unless
the "-p" switch is specified.
You can supply one or more filenames for files containing lists of
files to be added to an archive. The filenames must be listed one
per line with no leading or trailing blanks. The list filename(s)
must be prefixed with "!". Because of the list filename syntax,
you cannot specify a filename or wildname beginning with "!".
You can in ARJ 0.20 exclude filenames/wildnames from the list of
filenames to be processed by ARJ.
Example: ARJ a software *.* -x*.exe -x*.obj adds all files
in the current directory except .EXE and .OBJ files.
ARJ COMMANDS:
a: Add files to archive
This is the basic command to add disk files to an ARJ archive.
You can specify 0 to 64 filename arguments (one can be a
destination directory). The arguments can be wildnames. If
you specify the "-r" switch (recurse subdirectories), ARJ
will add all of the files in all of the subdirectories that
match the specified wildname.
Example: ARJ a -t archive subdir\*.*
Archive all files in directory "subdir" in text mode.
c: Comment archive files
This command allows you to comment the header and individual
files. ARJ will prompt you for each comment. The user will be
prompted for up to 25 lines for each comment. A line containing
only a [return] will terminate the comment.
The user can elect to input comment data from a file by entering
the comment filename preceded by an "!" as in "!archive.txt"
starting in column 1 of the first comment line.
To erase a comment from an archive, type [space] [return] on the
first comment line and [return] on the second comment line.
To add only the archive comment and not file comments, use the
following command:
ARJ c archive ...
The "..." will not match any filenames.
d: Delete files from archive
This commands allows you to delete files from the archive. When
wildcard selection is not suitable, you can use the "-q" switch
which causes ARJ to prompt you for deletion for each file
selected.
Example: ARJ d archive *.c
Delete all files in archive ending in ".c".
ARJ d archive *.c -q
Prompt before deleting files ending in ".c".
e: Extract files from archive
This command will extract one or more files from the archive to
the current directory or base directory if specified. ARJ will
prompt the user before overwriting existing files unless the
user specifies the "-y" switch. If the user gives a "no"
answer, ARJ will prompt for a new filename. If the user enters
a single [return] instead of a filename, ARJ will skip the
current file extraction.
When extracting a file located on multiple volumes, ARJ may
prompt the user with an "Append? " like prompt. This will
usually occur with files split across volumes.
Example: ARJ e archive soft\ *.c
Extract all files ending in ".c" to subdirectory
"soft".
f: Freshen files in archive
Update matching files in the archive that are OLDER than the
selected disk files.
Example: arj f archive *.c *.h
l: List contents of archive
List contents of archive to standard output. The display can be
paused after each screenful with the "-jp" switch. The files
are listed in stored order. There are no sort options
currently.
The last field on the display TPMGVX stands for:
T -> text/binary mode
P -> path information available in "V" listing
M -> compression method used
G -> file has been garbled (encrypted)
V -> archive has been continued to another volume
X -> this file is an extended portion of a larger file
Example: arj l archive *.c *.h
m: Move files to archive
This command is the same as specifying the "a" command with the
"-d" switch. The "m" commands adds the selected files to the
archive. If the adds are successful, then the added files are
deleted. The move command does not ask permission before
deleting the files. Use the "-d" switch for that feature.
Example: ARJ m archive soft\*.*
n: reName files in archive
This command allows you to change the names of the files stored
in an ARJ archive. ARJ will prompt for the new name of each
selected file. You can skip changing the name of a particular
file by entering a blank line.
Example: ARJ n archive *.c
In the above example, ARJ prompts for new names for all *.c
files.
p: Print files to standard output
Output files to standard output. This function works such that
the output file will contain only the file data extracted. This
is important for UNIX-like usage.
Example: ARJ p archive manual.doc > output.fil
In the above example, output.fil will be an exact copy of
manual.doc. There will be no extraneous header information in
output.fil. All extraction phase information is written to the
STDERR device, which is normally the display screen.
NOTE: Because of a problem using fwrite() and STDOUT, errors
occurring during redirection to serial and printer ports may not
be detected. Errors during redirection to disk files will be
detected.
r: Remove paths from filenames
This command causes ARJ to remove the path component from the
specified filenames stored in the archive. The default is all
filenames stored in the archive. This command is useful if you
forgot to specify "-e" to exclude paths.
s: Sample files to screen with pause
This command is similar to the "p" command except that one
screenful of data is displayed to the user and a user action is
then requested. The action prompt can be suppressed with the
"-y" switch.
The "s" command filters the text to output by truncating at 79
characters per line and displaying '?' for control characters.
t: Test integrity of archive
Test the contents of the selected files for the correct CRC
value. ARJ uses a 32 bit CRC to validate the contents of the
files. The use of 32 bit CRCs is many times better than the
use of 16 bit CRCs for the detection of errors.
Use this command to fully test the security envelope on an
ARJ-SECURED archive.
u: Update files to archive
Update older files in the archive and add files that are new to
the archive.
Example: arj u software
w: Where are text strings in archive
This command will prompt the user for up to 20 text strings to
search for within the archive. The search is done with case
being significant. A count of all matches will displayed after
each individual file is scanned.
Search strings are limited to 79 characters.
Matches that span archive volumes will not be detected by
this string search.
v: Verbosely list contents of archive
This command lists the full pathname and comments of the archive
files as well as the same information as the "l" command.
Use the "-jp" switch to pause the output after each screen.
x: eXtract files with full pathname
This command extracts one or more files from the archive to
their full paths in the current directory or to the base
directory if specified. ARJ stores pathnames as if they were
children of the target directory. Any drive or root directory
specifications are stripped before storing unless the "-jf"
switch was specified.
Example: arj x archive *.c
ARJ SWITCH OPTIONS:
-: (all) skip any more switch options
The switch option "--" will cause ARJ to stop looking for any
more switch options on the command line. This is useful for
entering filenames beginning with "-".
Example: ARJ a archive -- -file
a: (afu) allow any file Attribute
By default ARJ will not select system or hidden files via
wildcarding unless the "-a" option is specified.
b: (afu) Backup changed files
This switch will select only files that have the archive bit
set.
If you specify the "-b1" option, the archive bits of all
archived files will be reset after a successful archive has been
built.
Example: arj a a:backup1 c:\*.* -b1 -r -va simulates BACKUP
command.
c: (All) skip time-stamp Check
Normally with the "u" and "f" commands, ARJ will only update
files to an archive which are newer. The "-c" switch will cause
ARJ to update the archive regardless of the date-time modified
time stamps.
When extracting files from an archive with the "-y" and "-f"
switches set, ARJ would normally skip extracting older files.
The "-c" switch will force ARJ to extract these older files.
d: (afu) with Delete (move)
This switch provides the standard MOVE command. Successfully
added files will be deleted. ARJ will prompt the user before
deleting the files unless the "-y" switch is specified. Also,
you can use the "m" command which does not prompt before
deleting the files.
ARJ a archive filename -d -y is equivalent to
ARJ m archive filename and
ARJ a archive filename
delete filename
e: (afu) Exclude paths from filenames
By default ARJ always stores the pathname of the archived file.
This switch will cause ARJ to store only the filename component.
Normally, ARJ strips any drive letter and root symbol from
pathnames. If you specify the "-jf" switch, ARJ will keep the
drive and root as in C:\TEMP\FILES.
The "-e1" switch option causes ARJ to NOT store the base
directory name with the filenames in the archive.
Example: ARJ a archive C:\SOFTWARE\ARJ\ *.* -r -e1
In the above example, ARJ will NOT store the C:\SOFTWARE\ARJ\ as
part of the filenames.
f: (All) Freshen existing files
This switch causes ARJ to only extract newer files from the
archive.
g: (All) Garble with password
This switch followed by a password "-gpassword" will encrypt or
decrypt an archived file. During a "l" or "v" command, a
garbled file will display an "G" after the method number.
Example: ARJ e archive -gpassword
IMPORTANT INFORMATION: Due to a bug in previous versions of
ARJ, certain files that are stored with method 0 with a password
will not be extractable. You will see CRC errors reported.
This version of ARJ has a temporary option "-jg" that will
extract those garbled files.
Example: ARJ e archive -gpassword -jg
i: (All) with no progress Indicator
Do not display the percentage progress indicator. The progress
indicator appears during the add, extract, search, and test
operations.
j: (All) selects alternate set of switch characters.
This switch toggles the set of switch characters. For example,
"-ja" is not the same function as "-a".
k: (Upd) Keep archive file backup
Backup the original archive file during an update. The old
archive will be suffixed with ".BAK". Any existing ".BAK" file
will be overwritten.
l: (All) create List_name file
This switch will cause ARJ to dump to the filename after the
"-l" switch all of the filenames to be processed by this ARJ
command. This list contains all files that matched the file
wildnames given on the command line.
This list file can be used as a listfile on the command line.
Example: ARJ a -lname.lst archive *.exe
This example will create a file named "name.lst" with all *.exe
files.
m: (afu) with Method 0, 1, 2, 3, 4
Method 0 = storing (no compression)
Method 1 = maximum compression
(requires 334,000 plus bytes memory)
Method 2 = slightly less compression
(requires 256,000 plus bytes memory)
Method 3 = less compression
(requires 272,000 plus bytes memory)
Method 4 = fastest compression
(requires 256,000 plus bytes memory)
Example: ARJ a archive *.exe -m2
Method 1 and 2 are similar. Method 2 uses less memory and
produces slightly less compression.
Method 3 is very fast and gives compression slightly less than
PKZIP, PAK, and LHARC.
Method 4 uses a different decoder than 1 to 3. Method 4 is
provided as a fast compression format. It is comparable in
speed to PKZIP but provides slightly less compression.
IMPORTANT INFORMATION: ARJ 0.20 method 4 has been improved in
size compression but is NOT compatible with versions earlier
than 0.15. However, ARJ 0.20 will still extract and test
method 4 files correctly, but future versions of ARJ may not
have that capability. The new method 4 is more effective with
files over 8000 bytes in size. NOTE that the use of method 4 is
purely user specified. ARJ will never by default use method 4.
Methods 1, 2, and 3 are slightly different from earlier
versions, but are STILL compatible with earlier versions. The
method 1 in ARJ 0.15 no longer exists because of the time
penalty. Archives created by 0.15 are still compatible with
all versions of ARJ (0.13 to 0.20).
n: (All) only New files (not exist)
Only archive or extract files that do not exist in the target
archive or directory.
o: (All) On or after date YYMMDDHHMMSS
The switch "-o" by itself means select files modified today. If
"-o" is followed by a date and optionally a time, ARJ will only
select files modified on or after that date-time.
Example: ARJ a test -o9001021700 means select files modified
on or after Jan 2, 1990, 5:00 PM.
Years less than "80" will be considered as 21st century years.
There is no option for using other date-time formats.
The switch "-ob" selects files modified before today. If "-ob"
is followed by a date and optionally a time, ARJ will only
select files modified before that date-time.
p: (All) match using full Pathnames
By default ARJ normally uses just the filename component to
match files within the archive. When "-p" is specified, ARJ
looks for an exact path match, and then, looks for a filename
component match.
You should use the "-p" switch when updating an archive built
with the "-r" switch.
q: (All) Query on each file
This switch causes ARJ to prompt the user prior to acting upon
each archived file for all but the "l", "t", "v", and "w"
commands. This allows you to selectively delete, add, etc.
r: (All) Recurse subdirectories
This switch will cause ARJ to recurse any wildcards specified on
the command line including ARJ archive filenames by traversing
all subdirectories scanning for matches.
ARJ will also recurse non-wildcard filenames as in:
ARJ a archive FILE.BBS -r
You should use the "-p" switch when updating an archive built
with the "-r" switch.
s: (Upd) set archive time-Stamp
This switch causes ARJ to set the date-time stamp of the archive
to that of the newest file in the archive.
This option will also work with non-update commands as in:
ARJ l archive -s ...
t: (afu) archive file in Text mode
This switch causes ARJ to open and read the file to be archived
in text mode. This option should not be used on non-text files.
The "-t" switch is equivalent to "-t1".
If you specify the switch "-t0", ARJ will always use the binary
mode even for freshening files already in the archive.
u: (All) Update files (new and newer)
This switch causes ARJ to archive or extract newer and
non-existing files.
v: (All) enable multiple Volumes
This switch allows the creation of multiple volumes in the ADD
mode. The command "arj a a:arjvol \*.* -b -r -v360000" allows a
user to backup up all files changed since the last backup to
multiple floppy disks. ARJ will pause between volumes to allow
changing disks. Subsequent volumes will be suffixed .A01, .A02,
.A03, ... , .A99, .A00, .A01, etc.
Archived files can be split across volumes. ARJ will try to
fill each volume to within 200 to 3000 bytes of specified
maximum size.
The command "arj x a:arjvol -v" would restore files starting
from arjvol.arj. You must specify the entire ARJ volume name
including the .Ann suffix when starting from the middle of a
series of volumes.
The pauses between volumes can be suppressed with the "-y"
switch. You should not suppress the pauses when archiving to
diskettes.
Because of the splitting process, archived split files with a
size of zero bytes are possible. This is not an error.
If you comment your archives with long comments, you should take
that into account when specifying volume size. You should
specify a smaller volume size during the "a" command before
adding the comments.
The "-v" switch will accept the abbreviations 360, 720, 1200,
and 1440.
The "-vv" switch turns on the next volume beep option. When you
select this option, ARJ will sound a beep prior to the next
volume. The "v" modifier must come before any other modifier.
The "-va" switch sets the disk space auto-detect option. ARJ
will check for the disk space available on the target directory
and try to use all or most of it. This option is aimed at
diskette usage.
Examples: ARJ a A:backup -b -va
ARJ a backup -v360
The switch modifier "s" can be used to make ARJ execute one
specified system command prior to each volume or make ARJ pause
for manual execution of system commands. This is useful for
purging target diskettes before ARJ writes to them. The "s"
modifier must following the "a" modifier or the volume size.
Optionally, after the "s" modifier, you can specify a system
command or batch file name. ARJ will automatically execute the
command or batch file before each volume. If the command has
embedded blanks, then the entire switch option must be
surrounded by double quotes.
Examples: ARJ a A:backup -vas
ARJ a A:backup -vvas
ARJ a A:backup -v360s
ARJ a A:backup -vv360s
ARJ a A:backup -vaspurge.bat
ARJ a A:backup -v360sdelete.bat
ARJ a A:backup "-vasFORMAT A:"
Volume archives can be used as stand-alone archives save for the
files that are split across volumes.
It is recommended that the "-jt" (test archive) option be used
with the "-v" switch to ensure perfectly built volumes as it is
tedious to retest volumes after they are built.
WARNING: Updating multiple volume archives with the "-v" switch
set is NOT recommended, especially if the new file sizes are not
identical.
w: (Upd) assign Work directory
By default, ARJ builds a new ARJ archive file in the same
directory as the old archive file. By specifying the "-w"
switch, you can specify the working directory where the
temporary archive file will be built. After the temporary
archive file is built, it is copied over the original one and
deleted.
Normally ARJ requires enough disk space for the original archive
and the new temporary archive. Specifying the "-w" switch
allows you to move some of that disk space need to another
directory.
If the copy of the temporary archive on top of the original
archive fails, you will have to manually do the copy. ARJ will
not delete the temporary archive in this case.
Example: ARJ a -we:\temp\ archive *.c
x: (All) Exclude filenames
This switch is used to exclude filenames or wildnames from the
list of filenames to be processed.
Example: ARJ a archive soft\*.* -r -x*.exe -x*.obj -xtest
This example will archive all files in the soft directory and
sub-directories with the exception of any files named "test"
or ending in ".exe" and ".obj".
You can also specify an exclude file list by preceding the
filename with the "!" character. The exclude file list must
contain a list of filenames/wildnames one per line with no
leading or trailing blanks.
Example: ARJ a archive soft\*.* -r -x!exclude.lst
A maximum of 8000 filenames or wildnames can be excluded.
y: (All) assume Yes on all queries
Use this switch for batch type uses of ARJ. This switch
disables most of the normal user queries during ARJ execution.
Use this switch to suppress overwrite queries in the "e" and "x"
commands, to suppress the make new directory query in the "e"
and "x" commands, to suppress the pause during the "s" command
and to suppress the next volume pause using the "-v" option.
Use this option with due caution, especially during extraction
as this sets ARJ to overwrite files.
ja: (All) show ANSI comments
Display any ANSI escape sequences unaltered. By default, escape
characters in comments are not displayed. In ARJ 0.20, IBM
graphics characters will always be displayed.
jc: (All) test for Console RAW mode
In MS-DOS environments where the console input is RAW and not
cooked (tested for CTL C, CTL S, etc.), ARJ may hang up the
system at the first ARJ user prompt. As a temporary facility,
the "-jc" switch causes ARJ to test the STDIN device for RAW
mode. If the STDIN device is in RAW mode, ARJ will switch to
using CGETS() instead of ANSI FGETS() for input.
Example: ARJ e archive -jc
A convenient method of using this switch would be to include it
in the ARJ_SW environment variable.
Example: set arj_sw=-jc
If this option proves to be stable and reliable, it will become
the default and the "-jc" option will become unnecessary.
je: (Upd) create self-Extracting archive
This option causes ARJ to create a self-extracting .EXE file
instead of an .ARJ file. This self-extractor is about 14,600
bytes in size and supports full pathname extraction. The
current commands ARJSFX supports are:
Usage: ARJSFX [-command] [-switch(s)] [directory\] [file(s)]
Commands:
e: Extract files (default)
l: List contents v: Verbosely list contents
t: Test contents x: eXtract files with pathname
Switches:
a: show ANSI comments n: only New files (not exist)
c: skip time stamp Check p: match with Pathname
f: Freshen existing files u: Update files (new + newer)
g: unGarble with password y: assume Yes on queries
NOTE!!! ARJSFX uses the "-" character before all commands and
switches. This is to allow extraction of files named e, l, etc.
ARJSFX does not support compression method 4.
The ARJSFX module supports the ARJ-SECURITY envelope feature by
itself. The ARJ-SECURITY feature is only available as a
licensed option. It is intended as a feature for software
developers.
ARJ will create a self-extracting module without an intermediate
archive file.
Example: ARJ a software *.* -je
If you want to make a self-extracting module from an ARJ
archive, use the freshen command with a non-existent filename
argument such as "...". In this case, ARJ will report the
self-extractor created with 0 file(s). The 0 file(s) indicate
that no files were modified during the self-extractor creation.
Example: ARJ f software ... -je
jf: (afu) store Full specified path
Normally, ARJ will strip all pathnames of drive letter and root
symbol. This switch disables this action. When extracting with
the "x" command from an archive that was built with this switch,
you should NOT use the base directory option on the command
line.
jk: (Upd) Keep temp archive on error
When the "-jk" switch has been specified, ARJ will keep the
temporary archive during an aborted archive build/update. During
a failed build, ARJ will modify the temporary archive to make it
useable by removing the broken portion.
jp: (lv) Pause after each screenful
This switch will cause ARJ to pause after listing each screenful
of data for the "l" and "v" commands. Press the ENTER key to
continue the listing. You can also enter "quit" to exit ARJ.
In one special case, "ARJ -? -jp", the use of the -jp switch
toggles page pauses off, because by default, pausing is on.
jr: (All) Recover broken archive files
This switch is used to access headers and files in an archive
that has been corrupted either with bad data or missing data.
This switch lets ARJ find the next valid header for listing,
extraction or testing. ARJ will continue to look for headers
until it finds the end of file. At that point ARJ will print an
error message stating that it encountered the end of file
unexpectedly. This is to be expected.
If file header data has been corrupted, ARJ will be unable to
recover any file data associated with that header. If file data
has been corrupted, ARJ will abort but not delete any extracted
file data. To continue recovering from such a corrupted
archive, simple specify one filename to extract at a time or use
the "-q" query switch to prompt for individual files.
Example: ARJ e archive -jr -q
js: (afu) Store archives by suffix
This switch is used to force ARJ to store and not compress files
with the following extensions: .ARJ, .ZIP, .LZH, .PAK, .ARC.
The file extensions can be specified as follows:
ARJ a archive -js.zoo.ice.gif
The above command will store files with extensions ending in
.ZOO, .ICE, and .GIF. This overrides the defaults.
You can use the environment variable ARJ_SW to set up your own
defaults as follows:
set arj_sw = -js.arj.zip.lzh -js-
The "-js-" turns off the option by default so that when you
specify the "-js" switch on the command line, ARJ will already
know what extensions that you want to store.
jt: (Upd) Test temporary archive
This switch causes ARJ to execute an archive integrity check on
the intermediate temporary archive before overwriting any
pre-existing original archive. If any error occurs, ARJ will
not overwrite the original archive. When using the "-w" switch,
ARJ will test the final archive file before deleting any files.
Example: ARJ m archive *.c -jt
ju: (All) translate UNIX style paths
This switch causes ARJ to translate any subsequently encountered
pathnames to MS-DOS style from UNIX style. This switch also
causes translation of filenames entered as a result of ARJ
prompts such as in comment filenames.
Example: ARJ a archive -ju /soft/*.c
jv: (All) set Verbose display
This switch sets ARJ to display more information during the
"t"est, "l"ist, "v"erbose list, and "ex"tract commands.
Example: ARJ l archive -jv
jx: (afu) start at eXtended position
This switch is used to continue a file on another archive
manually. This switch is normally used when a multiple volume
"a" command has aborted.
Example: ARJ a arjvol.a01 manual.doc -jx100000
This example archives manual.doc starting from file byte
position 100000 and on.
ARJ_SECURITY ENVELOPE:
The ARJ-SECURITY ENVELOPE feature provides a facility similar to
other archivers. This feature disallows any type of modification,
even commenting, to an ARJ-SECURED archive by ARJ. Moreover, there
are additional internal checks to determine if the ARJ-SECURED
archive has been modified in any way. This feature is intended for
use by software developers who distribute their software in
archived format. However, there can be no guarantee that computer
pirates will not defeat this mechanism.
In normal use, ARJ will display one of two messages when processing
an archive with a valid ARJ-SECURITY envelope. ARJ will either
state that the archive MAY have a valid ARJ-SECURITY envelope or
that the archive HAS a valid ARJ-SECURITY envelope. ARJ can only
be sure that the envelope is valid when the "t", "e", or "x"
command is executed on ALL of the archived files. In order to
fully test the security envelope of an archive, use the "t" command
as in "ARJ t archive".
If the security envelope has been tampered with or the archive has
suffered data corruption, ARJ will display a message stating that
the security envelope has been violated.
KNOWN ARJ ISSUES/PROBLEMS:
When using a working directory, ARJ does not check for disk space
before overwriting the original archive. Be sure you have enough
space before updating an archive using the "-w" switch.
DO NOT continue to use older versions of ARJ earlier than 0.15a.
ARJ archives that have been created with 2048 byte sized comments
will produce unpredictable results when processed by older versions
of ARJ.
ARJ TECHNICAL SUPPORT:
I have received many useful suggestions from users all over the
world. Many of those suggestions are in this version or will be
incorporated in later versions of ARJ.
I will try to resolve software problems with ARJ as they become
known to me. Please notify me of any ARJ problems by mail, email
or via the ARJ support BBSes mentioned below. Despite the fact
that ARJ is free for non-commercial use, I will strive to make ARJ
a robust, stable and useful product for all users.
ARJ AVAILABILITY:
The latest version of ARJ can obtained from the following sources:
ARJ SUPPORT BBSes:
Wonderland BBS, Billerica, MA, BBS (508) 663-6220
This BBS receives ARJ directly from the author.
Dimensional Crossroads BBS, Brockton, MA, BBS (508) 427-5379
This BBS receives ARJ directly from the author.
If you run a BBS and would like to support ARJ and get updates as
soon as they are released, please contact me. I am looking for a
few more support sites.
OTHER BBS ARJ SOURCES:
Channel 1 BBS, Cambridge, MA, BBS (617) 354-8873
ARJ is available from a number of other BBS's, but I can only vouch
for the integrity of the archive if the ARJ020.EXE verifies its
ARJ-SECURITY envelope as valid. If no security envelope exists,
then the data has been re-archived and there is no assurance of
data integrity.
If none of the above sources is suitable, you may order a copy of
the latest version of ARJ directly from the author.
Send a check or money order for five dollars (US) to cover the
costs of shipping and handling for U.S. delivery. For foreign
delivery, send ten dollars (US) to cover shipping and handling.
Please specify diskette size (3.5 or 5.25 inch); otherwise, a 5.25
inch diskette will be shipped. Please allow a few weeks for
delivery, longer for foreign deliveries.
Robert Jung, 2606 Village Road West, Norwood, Massachusetts 02062
ACKNOWLEDGEMENTS:
LHARC is the name of an archiver by Haruyazu Yoshizaki.
PKZIP and ZIP are trademarks of PKWare, Inc.
PAK is trademark of NoGate Consulting.
I wish to express my gratitude to Haruyasu Yoshizaki (Yoshi) for
developing LHARC and distributing its source code. LHARC gave me
the impetus to start studying data compression. I also wish to
thank Haruhiko Okumura for providing additional ideas.
I wish to thank those who have helped in the development of ARJ.
Those include Ron Freimuth, Michael Lawler, Arkady Kleyner, Joseph
Teller, Brian Godette, and Jonathan Forbes.
I wish to thank my wife, Susan, and my son, Timothy, for putting up
with this ARJ obsession for the last few months. Without their
encouragement and support, ARJ would never have come to be.
But my greatest thanks goes to Almighty God for His inspiration and
great salvation.
USAGE AND DISTRIBUTION POLICY:
See LICENSE.DOC file for license policy.
FINAL COMMENTS:
I do hope that you find this program as useful as I have. I would
appreciate any suggestions to improve this archiver. I do have
another archiver called ARJX which is completely compatible with
ARJ and provides slightly tighter compression at two to three times
the speed using a proprietary compression algorithm. ARJX will not
be released until early 1991 at the earliest. The file RESULTS.DOC
shows the ARJX performance.
I can be reached at:
Robert Jung at the Wonderland BBS (508) 663-6220
Robert Jung at the Dimensional Crossroads BBS (508) 427-5379
Robert Jung at the CHANNEL 1 BBS (617) 354-8873
Robert Jung in the COMPRESS (ILINK), or LHARC / COMPRESSIONS
(SMARTNET) echo conferences.
Internet address until Jan 31, 1991, rjung@s37.prime.com
2606 Village Road West
Norwood, Massachusetts 02062
CompuServe userid: 72077,445 (Checked once or twice a week)
Internet address: 72077.445@compuserve.com
RECENT DATA COMPRESSION RESEARCH:
The following information is explained in more detail in the book,
TEXT COMPRESSION by Timothy Bell, John Cleary and Ian Witten
published by Prentice Hall, 1990. ISBN 0-13-911991-4.
Three of the most useful types of data compression involve context
modeling, Lempel-Ziv 1977, and Lempel-Ziv 1978.
Context models use the preceding few characters to PREDICT
(estimate the probability of) the next character. For example,
what is the next character after "tabl"? There is a high
probability that the character is "e". Much of today's research is
focused on these types of data compressors because they provide the
best "TEXT" compression results. The disadvantage of this family
of compressors is the amount of memory required. Three practical
models require from 500,000 to 5,000,000 bytes of memory.
More familiar is the Lempel-Ziv 1978 (LZ78) family of data
compressors. This family as well as Lempel-Ziv 1977 are classified
as adaptive dictionary encoders. In these methods, text strings
are replaced by pointers to previous occurrences of duplicate
strings. For example, the words in this document could be
represented by dictionary page and line numbers. The significant
characteristic of LZ78 algorithms is the parsing of previous text
data into PHRASES that are stored in a dictionary. Pointers are
allowed to reference such phrases; however, pointers are not
allowed to reference substrings of such phrases.
Lempel-Ziv-Welch, 1984, (ARC shrinking, crushing, UNIX COMPRESS) is
the most familiar of this family. Numerous articles have been
published concerning this method. Unknown to many is the fact that
this algorithm has a US patent number owned by UNISYS. These
algorithms are FAST. Their disadvantages include the problem of
handling a FULL dictionary when the input text data no longer
matches the contents of the dictionary and the poor compression of
non-text data.
Lempel-Ziv 1977 (LZ77) algorithms have recently come into popular
practical use (LHARC, PKZIP 1.10, ARJ, PAK). In the original LZ77
scheme, pointers are allowed to reference any phrase in a
fixed-size window that precedes the current phrase. A matched
current phrase is replaced by the pointer to the previously
occurring duplicate phrase. This pointer in LZ77 consists of an
offset into the window and the length of the phrase. The original
implementation was considered impractical as it used a brute force
string searching method to find duplicates. It was quite slow
requiring up to N character comparisons in an N sized window for
each phrase looked for.
However, in 1987, Timothy Bell proposed using a binary tree to
index into the window to speed the lookup of phrases. This
provided an order of magnitude speed increase. In the same year,
Brent published an algorithm that used a secondary compression
method (Huffman encoding, 1952) to further encode the output of a
LZ77 encoder. Huffman encoding is the subsitution of variable
bit-length codes for standard codes (8-bit ASCII) based upon
frequency of occurrence. The most frequent codes have the shortest
bit-lengths.
LHARC is a combination of these two ideas. It uses a binary tree
LZ77 encoder with dynamic Huffman encoding (1978) of the output.
The advantage of using dynamic Huffman encoding is adaptivity to
rapidly changing data. The disadvantage is slow decoding.
PKZIP 1.0, I believe, uses a combination of binary tree encoding
with SHANNON-FANO (1949) static encoding. Static SHANNON-FANO
encoding has the advantage of fast decoding and the disadvantage of
less optimal compression especially on rapidly changing data.
PKZIP will perform better in compression than LHARC on many large
files because PKZIP uses a larger window (8K) than LHARC (4K).
LHARC will perform best on binary data with rapidly changing
characteristics like executables that include a lot of text data.
LH (LHarc 2.0), I believe, uses a digital TRIE LZ77 encoder with a
static Huffman encoder. It uses an 8K window. LH uses a
particularly efficient Huffman encoder which works on small data
sets. Many static encoders suffer from the cost of including the
table of codes with the encoded data. The digital TRIE has the
advantage of always producing the most recent match unlike binary
trees. This recency of match is significant when secondary
compression is used. Much of this work has been derived and
improved upon from literature published in the last two years.
ARJX improves upon LH by using a proprietary LZ77 encoder (1990)
that is one of the fastest available for limited memory use. This
encoder is not derived from any published literature.
It will be interesting to see if developers can significantly
improve upon LH since it is based upon the most recent published
research in data compression.
One of the most significant new encoders published is that of Fiala
and Greene, 1989. This method uses pointers that point to nodes in
the TRIE data structure as opposed to the phrases in the window.
This bypasses the problem of redundancy of phrases in any given
window. Since each node is unique, fewer pointers are needed and
thus are more easily compressed by a secondary compressor. This
technique is currently patent pending.
I hope that this synopsis of compression research has been
enlightening.
End of document
