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Update UNARC to Universal UNARC from Lars Nelson

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- Credit and thanks to Lars Nelson for providing an enhanced version of UNARC.
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File: UNARC.DOC
Subject: User Documentation for UNARC Program
Version: 1.6
Date: March 27, 1987
------------------------------------------------------------------------------
UNARC
CP/M Archive File Extraction Utility
Copyright (C) 1986, 1987 by Robert A. Freed
All Rights Reserved
This file provides user-level documentation and operating instructions for
UNARC version 1.6, released March 27, 1987. Refer to the notice at the end of
this file regarding rights of use and distribution of this program.
The release message file, UNARC.MSG, provides a list of all additional files
distributed with the current UNARC release and describes the program changes
from the previous version 1.4 and 1.5 releases.
ABSTRACT
--------
UNARC is a utility program for CP/M systems which allows the listing, typeout,
printing, checking, and extraction of subfiles contained in "archive" library
(*.ARC or *.ARK) files. These are commonly used for compressed file storage
on remote access bulletin board systems. UNARC provides the CP/M user the
ability to process such files after downloading them via modem from these
remote systems.
REQUIREMENTS
------------
UNARC requires CP/M version 2 or higher. The program is offered in two
versions. The standard version, UNARC.COM, requires a Z80 processor (or
compatible equivalent, e.g. HD64180 or NSC800). An alternate version,
UNARCA.COM, is provided for systems with 8080 or 8085 processors (or 16-bit
systems using the NEC V20 for CP/M emulation). Identical capabilities are
provided by the two program versions.
NOTE
Although UNARCA.COM can execute on ANY system capable of
supporting CP/M, it is larger and significantly slower than
UNARC.COM and should be avoided by users of Z80-based systems.
UNARC is written in Z80 assembly language and requires only 5K bytes of disk
storage (6K for UNARCA). As distributed, the program requires at least 30K
bytes of available memory space (TPA) for full support of all archive file
formats (31K TPA size for UNARCA). (Smaller systems may be able to use some
of the program's capabilities.)
ABOUT ARC/ARK FILES
-------------------
The files which UNARC processes utilize a format that was introduced by the
ARC shareware utility program, which executes on 16-bit computers running the
MS-DOS (or PC-DOS) operating system. This format has achieved widespread
popularity since the ARC program first appeared in March 1985, and it has
become the de facto standard for file storage on remote access systems
catering to 16-bit computer users. More recently this file format has
achieved increased popularity on RCP/M (Remote CP/M) systems.
NOTE
Most RCP/M system operators have adopted the convention of naming
CP/M archive files with the filetype ARK. This differentiates
these from MS-DOS archive files, which use the filetype ARC. This
is a naming convention only: There is no difference in format,
and UNARC will accept files of either type interchangeably.
An archive is a group of files collected together into a single file in such a
way that the individual files may be recovered intact. In this respect,
archives are similar in function to libraries (*.LBR files), which have been
commonplace on CP/M systems since 1982, when the original LU library utility
program was introduced by Gary P. Novosielski. (However, the two file formats
are not compatible.)
The distinguishing characteristic of an ARC archive is that its component
files are automatically compressed when they are added to the archive, so that
the resulting file occupies a minimum amount of disk space. Of course, file
compression techniques have also been commonplace in the CP/M world since
1981, when the public domain SQ and USQ "squeeze and unsqueeze" programs were
introduced by Richard Greenlaw.
The SQ/USQ programs and their numerous popular descendants utilize a well-
known general-purpose form of data compression (Huffman coding). This
technique, which is also utilized in ARC files, performs well for many text
files but often produces poor compression of binary files (e.g. object program
.COM files). The ARC program also provides an advanced data compression
method, which it terms "crunching." This method (which is based on the
Lempel-Ziv-Welch or "LZW" algorithm) performs better than squeezing in most
cases, often achieving 50% or better compression of ASCII text files, 15-40%
compression of binary object files, and as much as 95% compression of bit-
mapped graphics image files.
Five different methods are actually employed for storing files in an archive.
The method chosen for a particular file is the one which results in the best
compression for that file:
(1) No compression ("unpacked"). The file is stored in its original form.
(2) Run-length encoding ("packed"). Repeated sequences of 3-255 identical
bytes are compressed into a three-byte sequence.
(3) Huffman coding ("squeezed"). Each 8-bit byte (after run-length encoding)
is encoded by a variable number of bits, with bit length (approximately)
inversely proportional to the frequency of occurence of the corresponding
byte.
(4) LZW compression ("crunched"). Variable-length strings of bytes (in
theory, up to nearly 4000 bytes in length) are represented by a single
(maximum) 12-bit code (after run-length encoding).
(5) LZW compression ("squashed"). This is a variation of crunching which
uses (maximum) 13-bit codes (and no run-length encoding).
Note that since one of the five methods involves no compression at all, the
resulting archive entry will never be larger than the original file.
NOTE
The most recent release of the MS-DOS ARC program (version 5.20)
has eliminated squeezing as a compression technique. However,
UNARC continues to process squeezed files for compatibility with
archives created by earlier versions of ARC and by other MS-DOS
archiving programs (notably PKARC).
The squashed compression method was recently introduced by the
MS-DOS programs PKARC and PKXARC. UNARC can process files which
use this method, although it is not universally accepted by other
MS-DOS archive extraction programs (including ARC).
During its lifetime, the ARC program has undergone numerous revisions which
have employed different variations on some of the above methods, particularly
LZW compression. In order to retain compatibility with archives created by
earlier program revisions, ARC stores a "version" indicator with each file in
an archive. Based on this indicator, the latest release of the ARC program
can always extract files created by older releases (although it will only use
the latest data compression versions when adding new files to an archive).
NOTE
The current release of UNARC supports archive file versions
generated by all releases of the following MS-DOS programs through
(at least) the indicated program versions:
ARC 5.20 (24 Oct 86), by System Enhancement Associates, Inc.
ARCA 1.22 (13 Sep 86), by Wayne Chin and Vernon Buerg
ARCH 5.38 (26 Jun 86), by Les Satenstein
PKARC 2.0 (15 Dec 86), by Phil Katz (PKWARE, Inc.)
(UNARC does not recognize, but is unaffected by, the non-standard
archive and file commenting feature of PKARC.)
Although the above discussion has emphasized the origin of archive files for
the MS-DOS operating system, their use has recently spread to many other
systems. Programs compatible with MS-DOS ARC have appeared for UNIX, Atari
68000, VAX/VMS, and TOPS-20 systems. A CP/M utility for building archive
files will also be available in the near future.
For additional information about archive files and the MS-DOS ARC utility,
refer to the documentation file, ARC.DOC, which is available from most remote
access systems which utilize archive files. For additional information about
the LZW algorithm (and data compression methods in general), refer to the
article "A Technique for High-Performance Data Compression", by Terry A.
Welch, in IEEE Computer magazine, Vol. 17, No. 6, June 1984.
USING UNARC
-----------
The UNARC program provides an on-line help message, which is generated by
running the program with an empty command line:
A>UNARC
UNARC 1.6 27 Mar 87
CP/M Archive File Extractor
Usage: UNARC [d:]arcfile[.typ] [d:][afn] [N|P|C]
Examples:
B>UNARC A:SAVE.ARK *.* ; List all files in CP/M archive SAVE on drive A
B>UNARC A:SAVE.ARC *.* ; List all files in MS-DOS archive SAVE on drive A
A>UNARC SAVE ; Same as either of above
A>UNARC SAVE *.* N ; Same as above (no screen pauses)
A>UNARC SAVE *.DOC ; List just .DOC files
A>UNARC SAVE READ.ME ; Typeout the file READ.ME
A>UNARC SAVE READ.ME N ; Typeout the file READ.ME (no screen pauses)
A>UNARC SAVE A: ; Extract all files to drive A
A>UNARC SAVE B:*.DOC ; Extract .DOC files to drive B
A>UNARC SAVE C:READ.ME ; Extract file READ.ME to drive C
A>UNARC SAVE PRN.DAT P ; Print the file PRN.DAT (no formatting)
A>UNARC SAVE *.* C ; Check validity of all files in archive
As shown by this help display, the UNARC utility provides the following
capabilities:
(1) Listing the directory of an archive
(2) Extracting component files from an archive
(3) Typing the contents of a component file at the console
(4) Printing a component file directly on the CP/M list device
(5) Checking the validity of an archive and its component files
The particular operation to be performed is determined by the form of the file
parameter(s) in the command line, as described separately in the sections
which follow. The following characteristics apply to all operations:
The first command line parameter must specify the name of an archive file. A
drive name and filetype are optional. The filetype, if omitted, defaults to
"ARK" or, if no such file exists, the alternate (MS-DOS) default "ARC" is
assumed.
The standard CP/M terminal control characters, CTRL-S (to suspend console
output) and CTRL-C (to abort the program), may be used at any time. CTRL-K
may also be used as an alternate for CTRL-C. Printer output to the CP/M list
device may be obtained by typing CTRL-P at CCP command level before executing
UNARC.
In addition, by default UNARC will pause after every 23 lines of console
output. At this time, the message "[more]" will appear at the bottom of the
console screen. The listing may be resumed by typing any key (other than
CTRL-S, CTRL-C, or CTRL-K, which will function as described above). If the
space bar is used, one more line of console output will be displayed (over-
writing the "[more]" message) and the program will again pause. If any other
key is typed (e.g. RETURN), another 23 lines of output will be allowed to
scroll onto the screen before the next pause. (LINE FEED may be used to
prevent overprinting of the "[more]" line, e.g. for hard-copy terminals.)
If continuous display is desired, this automatic pause feature may be disabled
by specifying "N" at the end of the command line. The "N" must be the last
command line character, and it must be preceded by a space. Also, there must
be two preceding file parameters on the command line. E.g., note the
difference between the following commands:
A>UNARC SAVE N ; Typeout the file N. in archive SAVE
A>UNARC SAVE *.* N ; List all files in archive SAVE with no pauses
The N option may not be used in conjunction with the P (Print) or C (Check)
options.
LISTING AN ARCHIVE DIRECTORY
----------------------------
By default, UNARC produces a detailed console listing of the component files
in an archive. (In fact, there is no way to suppress this listing; it is
generated during all UNARC operations.) If only the archive file name appears
on the command line, UNARC will generate a complete directory of all component
files in the specified archive file. Otherwise, the second command line
parameter may be used to select a particular file to be listed (or group of
files, if it contains the ambiguous file specification characters "*" or "?").
If no disk drive name is provided for the second parameter, and this parameter
specifies a group of files, the directory listing is the only output generated
by the program.
A sample directory listing is illustrated here:
A>UNARC CODES
Archive File = CODES.ARK
UNARCU
Universal Archive File Extraction Utility
Version 1.0
Modified for Universal use by Lars Nelson
September 17, 2023
Modified for ZCPR3 by Gene Pizzetta
December 9, 1990
Original CP/M 2.2 version is
Copyright (C) 1986, 1987 by Robert A. Freed
All Rights Reserved
UNARCU allows the listing, typeout, printing, checking, and extraction of
member files contained in ARK and ARC archive files. These are commonly
used for compressed file storage on remote access bulletin boards. This is
a universal version and runs on the following CP/M compatible systems:
CP/M 2.2 with DRI CCP or ZCPRD&J
ZSDOS 1.2 and 2.0 with DRI CCP, ZCPRD&J or Zsystem
CP/M 3 with DRI CCP or Z3Plus
ZPM3 with DRI CCP or ZCCP
DU file specification is supported on all systems. If Zsystem is active
then named directories can be used and the bad directories flag is
automatically checked.
If datestamping is available then extracted files will recieve the ARK file's
stored date stamp. The program handles DateStamper, NZTIME and CP.M Plus
date stamping methods.
UNARCU requires at least 32K of free memory (TPA) for full support of all
archive file formats, but smaller systems may be able to use some of the
program's capabilities.
USAGE:
UNARCU {DU: or dir:}arcfile{.typ} {DU: or dir:}{afn.aft} {{/}options}
If a DIR or DU specification is not given for the archive file, the current
drive/user is assumed. The second filename, which can be ambiguous,
refers to a member file or files in the archive. DIR: file specification
only available when Zsystem is active. DU: specification always available.
If a DU or DIR specification is provided for the member filespec, it will be
extracted to that directory. To extract to the current directory, only a
colon is required. If a directory specification is given without a filename,
all files ("*.*") is assumed.
If no DU or DIR specification is given, UNARCU acts differently depending
on whether the member name is ambiguous or not. If the member name is
unambiguous, and the filetype is not restricted, the file will be typed to
the screen. If the member name is ambiguous, or if no member name is
given at all, a directory of the ARK will be displayed.
If no filetype is given for the archive file, UNARCU first tries ARK and then
ARC.
An on-line help message will be displayed if UNARCU is called with no
command tail or if the command tail is "//".
OPTIONS: Options may or may not be preceded by a slash, but the slash is
required if the options are not the third token (element) on the command
line.
C Check the validity of the archive and the given member
files. If a member filespec is not given, all files
("*.*") is assumed.
E Toggle erasing of existing files without asking on and
off. UNARCU may be configured to automatically erase,
during member file extraction, existing files in the
target directory that have the same name. Or it can
be configured to ask first. This option will turn off
user query before erasure, if it is on by default, and
vice versa.
N Toggle console paging on or off. UNARCU may be
configured to default to console paging or not. This
option will turn paging off, if the the default is on,
and vice-versa. Paging effects both archive directory
display and member file type-out. During member file
extraction, console paging is always off.
P Sends a member file to the printer (LST device). The
member name cannot be ambiguous. The file will be
printed continuously, with no formatting or paging.
UNARCU can be aborted at any time with ^C or ^K.
If screen paging is enabled, UNARCU pauses after the screen fills. The
listing may be resumed by typing any key other than ^S, ^C, or ^K. The
space bar displays one more line of output (overwriting the "[more]"
message) and the program will again pause. For hard copy terminals, line
feed may be used to prevent overprinting of the "[more]" line. If paging
is disabled, the display can be paused with ^S.
LISTING AN ARCHIVE DIRECTORY: UNARC always produces a detailed
console listing of all the member files of an archive, or of those members
which match the second file specification, if one is given. If no member
name is given, or if the member name is ambiguous, then UNARCU only lists
the directory, without doing anything else. (That is, unless the C option is
included.)
A sample directory listing:
A0>UNARCU CODES
Archive File = A0:CODES.ARK
Name Length Disk Method Ver Stored Saved Date Time CRC
============ ======= ==== ======== === ======= ===== ========= ====== ====
ABLE .DOC 24320 24k Crunched 8 11777 52% 30 Apr 86 10:50a 42C0
@@ -285,97 +115,82 @@ CHARLIE .TXT 234 1k Packed 3 99 58% 2 May 86 4:11p 8927
==== ======= ==== ======= === ====
Total 3 41706 42k 26626 36% 58A4
The listing is equivalent to the "verbose" listing of the MS-DOS ARC
program, with the addition of the "Disk" and "Ver" fields, which are unique
to UNARCU and previous UNARC versions. The listing requires 78-columns
of terminal width.
This listing is equivalent to the "verbose" listing of the MS-DOS ARC program
(with the addition of the "Disk" and "Ver" fields, which are unique to UNARC).
The listing requires a 78-column terminal width; there is currently no "short"
listing format.
"Name" is the filename which will be generated if the file is extracted by
UNARCU. This is not necessarily the same as the name recorded in the
archive file. Although CP/M and MS-DOS file naming conventions are
identical, two conversions are made to guarantee filename validity: Lower-
case letters are converted to upper-case and non-printing characters are
converted to dollar signs ("$"). Archive entries are usually maintained and
listed in alphabetical order.
"Name" is the file name which will be generated if the file is extracted by
UNARC on a CP/M system. (This is not necessarily the same as the name
recorded in the archive file. Although CP/M and MS-DOS file naming
conventions are identical, two conversions are made to guarantee file name
validity under CP/M: Lower-case letters are converted to upper-case, and
non-printing characters are converted to dollar signs, "$".) Archive entries
are usually maintained (and hence listed) in alphabetic name order.
"Length" is the uncompressed file length, i.e., the number of bytes the file
will occupy if extracted to disk, exclusive of any additional length imposed
by the file system. MS-DOS permits files of arbitrary lengths, but CP/M
restricts files to multiples of 128 bytes.
"Length" is the uncompressed file length, i.e. the number of bytes the file
will occupy if extracted to disk, exclusive of any additional length imposed
by the CP/M file system. Note that MS-DOS permits files of arbitrary lengths
(unlike CP/M which restricts all files to a multiple of 128 bytes).
"Disk" is the actual amount of space required to extract the file to a CP/M
disk, expressed as a multiple of 1K (1024) bytes. The number is dependent
on the output drive's allocation block size, which can range from 1K to 16K
bytes. Typically, 1K is used for single-density floppy disks, 2K for
double-density floppies, and 4K for hard disks. In the absence of an
explicit output drive, UNARCU uses the block size of the currently logged
drive, or a configured default size.
"Disk" is the actual amount of disk space required to extract the file to a
CP/M disk, expressed as a multiple of 1K (1024) bytes. Note that this number
is dependent on the disk data allocation block size. (CP/M permits various
block sizes, ranging from 1K to 16K bytes. Typical sizes are 1K for single-
density floppy disks, 2K for double-density floppies, and 4K for hard disks,
although these values are quite system-dependent.) In the absence of an
explicit output drive name, UNARC uses the block size of the default
(currently "logged") disk drive (i.e. the drive which appears in the CCP
prompt).
"Method" is the compression method used: "Unpacked", "Packed",
"Squeezed", "Crunched", "Squashed", or "Unknown!". If the method
"Unknown!" appears, it likely indicates a faulty archive file or a newer
compression method not yet supported by UNARCU.
"Method" is the compression method used, specified as "Unpacked", "Packed",
"Squeezed", "Crunched", "Squashed", or "Unknown!". If the method "Unknown!"
appears, it most likely indicates (if not a faulty archive file) a newer
release of the MS-DOS ARC program that supports a new compression method (or a
new variation of an existing method). In this case, a corresponding new
release of UNARC will be required to extract the file.
"Ver" is the version of compression method used. UNARC supports versions
1-9: unpacked files, versions 1 or 2; packed files, version 3; squeezed
files, version 4; crunched files, versions 5 and squashed files, version 9.
"Ver" further identifies the version of compression used. Currently, UNARC
supports versions 1-9: unpacked files can have versions 1 or 2; packed files,
version 3; squeezed files, version 4; crunched files, versions 5-8; and
squashed files, version 9. The highest version number associated with each
compression method is the one generated by the most recent release of the
MS-DOS ARC program.
"Stored" is the compressed file length, that is, the number of bytes
occupied by the file in the archive, not including the directory information
overhead, which adds an additional 29 bytes to each member file.
"Stored" is the compressed file length, i.e. the number of bytes occupied by
the file in the archive. (This does not include the overhead associated with
the directory information itself, which adds an additional 29 bytes to the
size of each component file.)
"Saved" is the percentage of the original file length which was saved by
compression; i.e., higher values indicate better compression. (The MS-DOS ARC
documentation refers to this as the "stowage factor.") The value shown on the
totals line applies to the archive as a whole, not including the directory
"Saved" indicates the percentage of the original file length which was saved
by compression. Higher values indicate better compression. The MS-DOS
ARC documentation refers to this as the "stowage factor". The value shown
in the totals applies to the archive as a whole, excluding directory
overhead.
"Date" and "Time" refer to the last file modification, as of the time it was
added to the archive. (Date and time stamping is, of course, one of the nice
features of MS-DOS which is lacking in standard CP/M 2.2.)
"Date" and "Time" are the file modification stamp at the time it was added
to the archive.
"CRC" is an internal 16-bit cyclic redundancy check value which is computed
when a file is added to an archive (expressed in hexadecimal). As a test of
file validity, UNARC re-computes this value when it extracts a file (see
below). Note that this value is calculated by a different method than that
used by either of the two popular public domain programs, CRCK and CHEK. (It
is however quite valid as a reliable error-detection mechanism.) This value
is shown in the listing for completeness only. The value shown on the totals
line is the 16-bit sum of all displayed CRC values. This is useful as a
single "checksum" value for comparing entire archives. (Since the CRC values
are computed before compression takes place, the total should be the same for
all archives created from the same set of input files, independent of any
particular variations in file order or compression methods.)
"CRC" is an internal 16-bit cyclic redundancy check value computed when a
file is added to an archive, expressed in hexadecimal. UNARCU checks file
validity by recomputing this value when it extracts a file. The value is
calculated by a different method than that used by either of the two
popular public domain programs, CRCK and CHEK, but it is a quite valid and
reliable error-detection mechanism. The value is given for completeness
only. The total in the last line is the 16-bit sum of the displayed CRC
values and is useful for comparing entire archives. Since the CRC values
are computed before compression, the total should be the same for all
archives created from the same set of input files, without regard for
variations in file order or compression methods.
The "Total" line is displayed only if multiple files appear in the listing,
and it includes a count of the number of files listed.
The "Total" line is displayed only if more than one file appears in the
listing.
EXTRACTING FILES FROM AN ARCHIVE: If the second command line
parameter contains a DU or DIR specification UNARCU will extract the
selected member file or files to to the indicated disk directory. If the
directory specification is given without a filename, all member files will be
extracted to the indicated directory. If only a colon is given, the current
drive/user will be assumed.
Below is a directory listing as might be generated during file extraction,
along with some possible warning messages:
EXTRACTING FILES FROM AN ARCHIVE
--------------------------------
If the second command line parameter contains a disk drive name, UNARC will
extract the selected file(s) from the archive to CP/M file(s) on the indicated
disk drive. If only a drive name appears, all component files of the archive
will be extracted. The following illustrates a sample archive directory
listing as generated during a file extraction operation:
A>UNARC CODES B:
Archive File = CODES.ARK
Output Drive = B:
A0>UNARCU CODES B1:
Archive File = A0:CODES.ARK
Output Directory = B1:
Name Length Disk Method Ver Stored Saved Date Time CRC
============ ======= ==== ======== === ======= ===== ========= ====== ====
ABLE .DOC 24320 24k Crunched 8 11777 52% 30 Apr 86 10:50a 42C0
@@ -388,236 +203,235 @@ CHARLIE .TXT 234 2k Packed 3 99 58% 2 May 86 4:11p 8927
==== ======= ==== ======= === ====
Total 3 41706 44k 26616 36% 58A4
"Replace existing output file (y/n)?" appears if a file of the same name
exists in the output directory, requiring a "Y" or "N" response. Any
response other than "Y" will be consided to be the same as "N". If UNARCU
has been configured to erase without query, this message will not appear.
The above listing also illustrates several warning messages which may occur
when extracting files from an archive.
The first two of the "Warning:" messages above indicate that either the
cyclic redundancy check (CRC) value or the extracted file length does not
match the value recorded in the archive header when the original file was
added. The third warning message is displayed if the proper format for
the beginning of a new member is not detected, but UNARCU recovered by
skipping a certain number of bytes in the archive file. If a recovery
attempt fails, UNARC aborts and issues a different message, "Invalid archive
file format". The appearance of any of these messages probably means the
file data has been corrupted in some way.
The message "Replace existing output file (y/n)?" appears if a file of the
same name already exists on the output drive. The user must answer "Y" (or
"y") to allow the extraction to proceed (in which case, the existing file is
unceremoniously deleted). Any other response will cause UNARC to preserve the
existing file, bypass the extraction operation for the current file, and
(except for a CTRL-C response) skip to the next file to be extracted (if any).
If the original MS-DOS file length was not an exact multiple of 128 bytes,
the final record of the extracted file will be padded with 1Ah characters
(ASCII ^Z).
The first two warning messages illustrated above are provided as a check on
the validity of the extracted file. These indicate that either the cyclic
redundancy check (CRC) value computed by UNARC, or the resulting extracted
file length, does not match the corresponding value recorded in the archive
when the original file was added to it. The final warning message occurs if
UNARC fails to detect the proper format for the start of a new subfile, but
can recover by skipping a certain number of bytes in the archive file. (If
the recovery attempt fails, UNARC aborts with the message "Invalid archive
file format.") The appearance of any of these messages most likely indicates
that the file data has been corrupted in some way (e.g. during modem
transmission from a remote system).
Disk space in the listing will be correct for the specified output directory.
In the two examples above, drive A has 1K allocation blocks while drive B
has a 2K blocks, which accounts for the differences in the two listings. To
determine the exact disk space requirements before extracting files, log
into the desired output drive and take an UNARCU directory listing of the
ARK file.
Note that if the original (i.e. MS-DOS) file length was not an exact multiple
of 128 bytes (as required by CP/M), UNARC will pad the final record of the
extracted file with hex "1A" (ASCII CTRL-Z) bytes. This provides the correct
end-of-file termination for text files, according to CP/M conventions.
If a file extraction is aborted with ^C, any partial output file will have to
be deleted manually.
Also, the disk space shown in the archive directory listing will be correct
for the specified disk drive. (In the above examples, drive A: has a 1K data
allocation block size while drive B: has a 2K block size, which accounts for
the differences in the two listings.) In order to determine the exact disk
space requirements in advance of a file extraction operation, the user may
first "log into" the desired output drive (i.e. select it as the default
drive), and run UNARC to obtain a directory listing only. (This is a
consideration only on systems with mixed disk drive types.)
A file extraction operation may be aborted at any time by entering CTRL-C from
the console. In this case, any partial output file will remain on disk and
should be deleted manually following the program abort. (Any existing file of
the same name will have already been deleted, however.)
TYPING OUT A FILE IN AN ARCHIVE
-------------------------------
A console typeout of the contents of a single component file in an archive may
be requested by specifying a non-ambiguous file name (and no disk drive name)
in the second command line parameter. For example:
A>UNARC CODES ABLE.DOC
Archive File = CODES.ARK
TYPING MEMBER FILES: Typing the contents of a member file in an archive
to the console may be requested by giving a non-ambiguous filename and no
output disk directory as the second command line parameter. For example:
A0>UNARCU CODES ABLE.DOC
Archive File = A0:CODES.ARK
Name Length Disk Method Ver Stored Saved Date Time CRC
============ ======= ==== ======== === ======= ===== ========= ====== ====
ABLE .DOC 24320 24k Crunched 8 11777 52% 30 Apr 86 10:50a 42C0
-------------------------------------------------------------------------------
This is file ABLE.DOC, contained within the archive CODES.ARK. Typeout will
proceed until the end of this file or may be aborted by CTRL-C.....
proceed until the end of this file, so you'd better be patient. For somebody
who has nothing to say, I've written an awfully big file here. If you don't
want to read all 24K of it, you can type ^C ....
The specified file is assumed to contain valid ASCII text data. All bytes
are masked to seven bits and all control characters are ignored except
horizontal tabs, which are expanded to blanks with stops at every eighth
column), and line feeds, vertical tabs, and form feeds, all of which generate
a new line. SUB (^Z) is interpreted as the end of the file. Backspaces and
carriage returns are ignored, so text will not be obscured.
UNARCU will refuse to type files whose filetype indicates are not ASCII text
files, including COM, CMD, EXE, OBJ, OVL, REL, PRL, CRL, IRL, INI, SYS,
BAD, ARK, ARC, LBR, ?Q?, ?Y? and ?Z?. If one of these or other restricted
types is given, directory information only is listed.
CRC and file length checking are not performed when a file is typed to the
screen.
PRINTING MEMBER FILES: A single member file may be sent to the printer
(CP/M LST device) with the "P" option as the third parameter on the
command line with or without a preceding slash. In addition, the member
name must be non-ambiguous and must not be preceded by a drive or user
specification. For example:
A0>UNARCU CODES CHARLIE.TXT P
or
A0>UNARCU CODES CHARLIE.TXT /P
The contents of the specified file is passed directly to the printer without
alteration, additional formatting, or even paging. The user should make
sure it contains data suitable for printer output. This unfiltered operation
is particularly well-suited for the output of binary graphics images to
dot-matrix printers. These files can be extremely large, but compress quite
well, often to less than 5% of their original size. The same filetypes
excluded from typing are also excluded from printing. Printing may be
paused or aborted with ^S and ^C respectively.
CHECKING MEMBER FILES: With the "C" option UNARCU can be directed to
extract one or more member files from an archive, without actually storing
them as disk files. This operation performs file CRC and length checking,
so it is useful for verifying correct modem data transmission of an archive.
If the "C" is the second parameter on the command line, it must be
preceded by a slash. In that case all files in the archive will be checked.
If a member filename is given, it may be ambiguous, but it cannot be
preceded by a disk directory specification. For example:
A0>UNARCU CODES *.DOC C
or
A0>UNARCU CODES /C
FILE DATE STAMPING: ARK and ARC files contain only a member file's
modification date and time. When a member is extracted under ZSDOS or
CP/M 3 with date stamping, its modification date will be transferred to disk
as both the create and modification file date stamps. If the modification
date is not included in the archive, then the extracted file will be stamped
with the current date and time.
SECURITY: Z-Node security is handled automatically by UNARCU when
Zsystem is running. If the Wheel byte is off (reset), file extraction,
archive checking, and file printing are all disabled. In addition, UNARCU
can be configured to disable file type-out or to limit type-out to a maximum
number of lines.
The specified file is assumed to contain valid ASCII text data. In
particular, all bytes are masked to seven bits, and all ASCII control
characters are ignored except for HT (horizontal tab, which is expanded to
blanks with assumed tab stops at every eighth column), LF, VT or FF (line
feed, vertical tab or form feed, which generate a new typeout line), and SUB
(CTRL-Z, which by CP/M convention indicates end-of-file and terminates the
typeout). Note that BS (backspace) and CR (carriage return) are ignored, so
that text will not be obscured within files which utilize these for over-
printing (i.e. when directed to a printer).
Directory security depends on the file specification parsing of ZCPR 3.3 or
higher to indicate that the DU or DIR are illegal. Security should be
adequate, however, under other CPR's.
The following filetypes, which are usually associated with binary (non-text)
data, are specifically excluded from typeout operations: COM, EXE, OBJ, OV?,
REL, ?RL, INT, SYS, BAD, LBR, ARC, ARK, ?Q?, and ?Z?. If one of these types
is specified, only the directory information for the requested file is listed.
PROGRAM CONFIGURATION OPTIONS: Several configuration bytes are
available to tailor the program for specific requirements, particularly for
RCP/M systems. With the Wheel byte off, UNARCU can be used by remote
callers only for archive directory listing and, optionally, for member file
typeout.
Note that CRC and file length checking are not performed during a typeout
operation, as they are during extraction to a disk file.
Configuration bytes also determine the default conditions for the N and E
command line options and the filetypes excluded from type-out.
Other configuration points are provided for non-standard systems and need
not concern the majority of users running ZCPR3, NZ-COM, or Z3PLUS.
Patching is accomplished using ZCNFG and the configuration file,
UNARCUnn.CFG, where nn is the current version. The options are discussed
in detail in the CFG file help screens. ZCNFG will find the CFG file
automatically, even if you change the name of the program, as long as you
do not change the name of the CFG file.
PRINTING A FILE IN AN ARCHIVE
-----------------------------
For most users no configuration is necessary.
A single component file in an archive may be output directly to the printer
(CP/M list device) by specifying a trailing "P" on the command line. The "P"
must be the last command line character, and it must be separated from the
second file parameter by a space. (The file parameter must specify a non-
ambiguous file name and no disk drive name.) For example:
ABOUT ARC/ARK FILES: The files which UNARCU processes utilize a format
that was introduced by the ARC shareware utility program, which executes
on 16-bit computers running the MS-DOS (or PC-DOS) operating system.
This format has achieved widespread popularity since the ARC program
first appeared in March 1985, and it has become the de facto standard for
file storage on remote access systems catering to 16-bit computer users.
This file format also achieved popularity on RCP/Ms (Remote CP/M) systems.
While ARC files have given way to ZIP files in general, many ARC files are
available on the web containing CP/M software.
A>UNARC CODES CHARLIE.TXT P
RCP/M system operators adopted the convention of naming CP/M archive
files with the filetype ARK. This differentiates these from MS-DOS archive
files, which use the filetype ARC. This is a naming convention only; there
is no difference in format, and UNARC will accept files of either type
interchangeably.
The specified file is assumed to contain data suitable for printer output and
is passed directly to the printer without alteration or additional formatting.
This operation is particularly well-suited for output of binary graphics
images on dot-matrix printers, since these can be extemely large but tend to
compress quite well (e.g. to less than 5% of their original size). Note that
the binary data filetypes which are excluded from typeout operations are also
excluded from printing operations. Printing may be paused or aborted by use
of the console CTRL-S and CTRL-C characters.
An archive is a group of files compressed and collected together into a
single file in such a way that the individual files may be recovered intact.
In this respect, archives are similar in function to libraries (LBR files),
which have been commonplace on CP/M systems since 1982, when the
original LU library utility program was introduced by Gary P. Novosielski.
The two file formats, however, are not compatible.)
The distinguishing characteristic of an ARC archive is that its component
files are automatically compressed when they are added to the archive, so
that the resulting file occupies a minimum amount of disk space. Of
course, file compression techniques have also been commonplace in the CP/M
world since 1981, when the public domain SQ and USQ "squeeze and
unsqueeze" programs were introduced by Richard Greenlaw.
The SQ/USQ programs and their numerous popular descendants utilize a
well-known general-purpose form of data compression (Huffman coding).
This technique, which is also utilized in ARC files, performs well for many
text files but often produces poor compression of binary files (e.g., object
program COM files). The ARC program also provides an advanced data
compression method, which it terms "crunching." This method (which is
based on the Lempel-Ziv-Welch or "LZW" algorithm) performs better than
squeezing in most cases, often achieving 50% or better compression of ASCII
text files, 15-40% compression of binary object files, and as much as 95%
compression of bit-mapped graphics image files.
CHECKING FILES IN AN ARCHIVE
----------------------------
Five different methods are actually employed for storing files in an
archive. The method chosen for a particular file is the one which results
in the best compression for that file:
1. No compression ("unpacked"). The file is stored in its
original form.
2. Run-length encoding ("packed"). Repeated sequences of 3-
255 identical bytes are compressed into a three-byte sequence.
3. Huffman coding ("squeezed"). Each 8-bit byte (after run-
length encoding) is encoded by a variable number of bits, with
bit length (approximately) inversely proportional to the
frequency of occurence of the corresponding byte.
4. LZW compression ("crunched"). Variable-length strings
of bytes (in theory, up to nearly 4000 bytes in length) are
represented by a single (maximum) 12-bit code (after run-length
encoding).
5. LZW compression ("squashed"). This is a variation of
crunching which uses (maximum) 13-bit codes (and no run-length
encoding).
UNARC may be directed to extract one or more component files from an archive,
without actually storing these as disk files, by specifying a trailing "C" on
the command line. This operation performs file CRC and length checking, and
it is useful for verifying correct modem data transmission of an archive. The
"C" must be the last command line character, and it must be separated from the
second file parameter by a space. (The file parameter must not specify a disk
drive name, which indicates extraction to disk.) To check an entire archive,
specify "*.*" for the second file parameter, for example:
Since one of the five methods involves no compression at all, the resulting
archive entry will never be larger than the original file.
A>UNARC CODES *.* C
The last release of the MS-DOS ARC program (version 5.20) has eliminated
squeezing as a compression technique. However, UNARC continues to
process squeezed files for compatibility with archives created by earlier
versions of ARC and by other MS-DOS archiving programs (notably PKARC).
The squashed compression method was introduced by the MS-DOS programs
PKARC and PKXARC. UNARC can process files which use this method,
although it is not universally accepted by other MS-DOS archive extraction
programs (including ARC).
During its lifetime, the ARC program has undergone numerous revisions
which have employed different variations on some of the above methods,
particularly LZW compression. In order to retain compatibility with
archives created by earlier program revisions, ARC stores a "version"
indicator with each file in an archive. Based on this indicator, the latest
release of the ARC program can always extract files created by older
releases (although it will only use the latest data compression versions when
adding new files to an archive).
PROGRAM OPTIONS
---------------
The current release of UNARC supports archive file versions generated by
all releases of the following MS-DOS programs through (at least) the
indicated program versions:
ARC 5.20 (24 Oct 86), by System Enhancement Associates, Inc.
ARCA 1.22 (13 Sep 86), by Wayne Chin and Vernon Buerg
ARCH 5.38 (26 Jun 86), by Les Satenstein
PKARC 2.0 (15 Dec 86), by Phil Katz (PKWARE, Inc.)
UNARC does not recognize, but is unaffected by, the non-standard archive
and file commenting feature of PKARC.
UNARC provides several options which may be used to tailor the program for
specific non-universal requirements. Many of these are intended for RCP/M
(Remote CP/M) system operators, to allow generation of a secure version of
UNARC which can be used by remote callers for purposes of archive directory
listing and/or file typeout only (but not file extraction). Others are
provided for specialized non-standard CP/M systems and need not concern the
majority of users running CP/M 2.2, CP/M 3.0 (CP/M Plus), or ZCPR3/ZRDOS
systems. Additional options provide user preference features (such as the
number of screen lines between console output pauses, or the list of filetypes
excluded from typeout operations).
Although the above discussion has emphasized the origin of archive files
for the MS-DOS operating system, their use did spread to many other
systems. Programs compatible with MS-DOS ARC have appeared for UNIX,
Atari 68000, VAX/VMS, and TOPS-20 systems. A CP/M utility for building
archive files is also available.
All of these options are described in UNARCOVL.ASM, an assembly language
source file that can be edited and assembled to generate a HEX-format overlay
for easy patching of the UNARC.COM or UNARCA.COM program files. Complete
details are provided for technically-oriented users in UNARCOVL.ASM. However,
the default options in the distributed program files are suitable for the
majority of users with standard CP/M operating systems.
PROGRAM DISTRIBUTION
--------------------
The UNARC program, its documentation, and all related files are distributed in
archive file format (of course!). The distribution file is named UNARCxx.ARK,
where "xx" is derived from the current version number (e.g. UNARC16.ARK for
version 1.6). (This does not include the program source code, which is
distributed separately.) This archive has the special characteristic that it
is "self-unpacking." I.e., a separate copy of the UNARC.COM program file is
NOT required to extract the component files from this archive.
The procedure for extracting the distribution files is quite simple: First,
copy or rename UNARCxx.ARK to a program file, UNARCxx.COM, on the current disk
drive. (Note that the filename, UNARCxx, must NOT be changed.) Then, run
this program with a single optional command line parameter specifying the disk
drive to which all distribution files will be extracted (defaults to current
drive).
For example, assuming UNARC16.ARK is on drive B: and the files are to be
extracted to drive C:, the following CP/M commands may be used:
A>B: ; Set current drive for UNARC16.ARK
B>REN UNARC16.COM=UNARC16.ARK ; Rename it to UNARC16.COM
B>UNARC16 C: ; Run it to extract all files to drive C:
Note that this self-unpacking capability is provided only by the distributed
archive file, and it will not work if that file is altered or reconstructed.
AUTHOR'S NOTE
-------------
I undertook writing the UNARC program to satisfy my curiosity about software
developments in the MS-DOS/PC-DOS world. At the time I began work on UNARC,
the MS-DOS ARC program had been in existence for over a year and had achieved
widespread popularity and acceptance in the 16-bit community. Unfortunately,
the lack of a compatible equivalent for CP/M systems rendered a large amount
of public domain software inaccessible to 8-bit users such as myself. (Note
that 16-bit software can indeed be of interest to users of 8-bit systems, e.g.
Pascal and C language programs.)
Also, an increasing number of RCP/M systems now cater to both 8-bit and 16-bit
users. Since the release of UNARC 1.0 (May 3, 1986), I have been encouraged
to see that the program has found a welcome home on many such systems.
Special thanks are due to Irv Hoff and Norman Beeler for providing archive
file support in the KMD20 and LUX52 series of programs, respectively. With
the increasing popularity of .ARC files on many different computer systems, I
believe that continued such support of this compression format is both
desirable and inevitable for CP/M systems. At the time of this writing I am
about to release NOAH, a companion program to UNARC which will allow CP/M
users to generate ARC-compatible files.
Bob Freed
March 27, 1987
NOTICE
The UNARC program and its associated documentation is the copy-
righted property of its author -- it is NOT in the public domain.
HOWEVER... Free use, distribution, and modification of these
files is permitted (and encouraged), subject to the following
conditions:
(1) Such use or distribution must be for non-profit purposes only.
(2) The author's copyright notice may not be altered or removed.
(3) Modifications to this program or its documentation files may
not be distributed without notification of and approval by
the author.
(4) The source program code may not be used, in whole or in part,
in any other publicly-distributed or derivative work without
similar notification and approval.
No fee is requested or expected for the use and distribution of
this program subject to the above conditions. The author reserves
the right to modify these conditions for any future revisions of
this program. Questions, comments, suggestions, commercial
inquiries, and bug reports or fixes are welcomed by the author:
Robert A. Freed
62 Miller Road
Newton Centre, MA 02159
Telephone (617) 332-3533
------------------------------------------------------------------------------

For additional information about archive files and the MS-DOS ARC utility,
refer to the documentation file, ARC.DOC, which is available on the web.
For additional information about the LZW algorithm (and data compression
methods in general), refer to the article "A Technique for High-Performance
Data Compression", by Terry A. Welch, in IEEE Computer magazine, Vol. 17,
No. 6, June 1984.


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