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1985-05-06
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ARC
File Archive Utility
(C) COPYRIGHT 1985 by System Enhancement Associates; ALL RIGHTS RESERVED
This file describes the ARC file utility, version 3.04, which was
created by System Enhancement Associates on 17 April 1985.
ARC is the copyrighted property of System Enhancement Associates. You
are granted a limited license to use ARC, and to copy it and
distribute it, provided that the following conditions are met:
1) No fee may be charged for such copying and distribution.
2) ARC must be distributed as a complete set of all files.
3) ARC may ONLY be distributed in its original, unmodified state.
Any voluntary contributions for the use of this program will be
appreciated, and should be sent to:
System Enhancement Associates
12 Franklin Avenue
Clifton, NJ 07011
ARC is used to create and maintain file archives. An archive is a
group of files collected together into one file in such a way that the
individual files may be recovered intact.
ARC is different from other archive and library utilities in that it
automatically compresses the files being archived, so that the
resulting archive takes up a minimum amount of space.
When ARC is used to add a file to an archive it analyzes the file to
determine which of three packing methods will result in the greatest
savings. These three methods are:
1) No compression; the file is stored intact.
2) Repeated-character compression; repeated sequences of the same
byte value are collapsed into a three-byte code sequence.
3) Huffman squeezing; the file is compressed into variable length bit
strings, similar to the method used by the SQ programs.
Note that, since one of the three methods involves no compression at
all, the resulting archive entry will never be larger than the
original file.
USING ARC
=========
ARC is invoked with a command of the following format:
ARC <x> <arcname> [<template> . . .]
Where:
<x> is an ARC command letter (see below), in either upper or lower
case.
<arcname> is the name of the archive to act on, with or without an
extension. If no extension is supplied, then ".ARC" is assumed.
<template> is one or more file name templates. The "wildcard"
characters "*" and "?" may be used.
If ARC is invoked with no arguments (by typing "ARC", and pressing
"enter"), then a brief command summary is displayed.
ARC COMMANDS
============
Following is a brief summary of the available ARC commands:
a,u = add files to archive
m = move files to archive
d = delete files from archive
x,e = extract files from archive
p = copy files from archive to stdout
l = list files in archive
b = retain backup copy of archive
w = suppress warning messages
n = suppress notes and comments
t = test archive integrity
These commands are explained in more detail below.
ADD FILES TO ARCHIVE
====================
Files are added to an archive using the "A" (Add), "U" (Update), or
"M" (Move) commands. Add and Update are identical. Move differs in
that the source file is deleted once it has been added to the archive.
For example, if you wish to add a file named "TEST.DAT" to an archive
named "MY.ARC", you would use a command of the form:
ARC a my test.dat
or:
ARC u my.arc test.dat
If you wanted to move all files in your current directory into an
archive named "SUM.ARC", you could use a command of the form:
ARC m sum *.*
If you wanted to add all files with a ".C" extension, and all files
named "STUFF" to an archive named "JUNK.ARC", you could type:
ARC a junk *.c stuff.*
Archive entries are always maintained in alphabetic order. Archive
entries may not have duplicate names. If you add a file to an archive
that already contains a file by that name, then the existing entry in
the archive is replaced. Also, the archive itself and its backup will
not be added.
DELETING FILES
==============
Archive entries are deleted with the "D" (Delete) command. For
example, if you had an archive named "JUNK.ARC", and you wished to
delete all entries in it with a filename extension of ".C", you could
type:
ARC d junk *.c
EXTRACTING FILES
================
Archive entries are extracted with the "E" (Extract) and "X" (eXtract)
commands. For example, if you had an archive named "JUNK.ARC", and
you wanted all files in it with an extension of ".TXT" or ".DOC" to be
recreated on your disk, you could type:
ARC x junk *.txt *.doc
If you wanted to extract all of the files in an archive named
"JUNK.ARC", you could simply type:
ARC x junk
Whatever method of file compression was used in storing the files is
reversed, and uncompressed copies are created in the current
directory.
PRINTING FILES
==============
Archive entries may be examined with the "P" (Print) command. This
works the same as the Extract command, except that the files are not
created on disk. Instead, the contents of the files are written to
standard output. For example, if you wanted to see the contents of
every ".TXT" file in an archive named "JUNK.ARC", but didn't want them
saved on disk, you could type:
ARC p junk *.txt
If you wanted them to be printed on your printer instead of on your
screen, you could type:
ARC p junk *.txt >prn
LISTING ARCHIVE ENTRIES
=======================
You can obtain a list of the contents of an archive by using the "L"
(List) command. For example, to see what is in an archive named
"JUNK.ARC", you could type:
ARC l junk
If you are only interested in files with an extension of ".DOC", then
you could type:
ARC l junk *.doc
ARC lists the archive contents in a table like this:
Name Length Comp SF Date Time
============ ======== ==== ==== ========= ======
ALPHA.TXT 512 -- 0% 13 Apr 85 0:29a
BRAVO.TXT 512 Pack 43% 15 Apr 85 11:51a
COCO.TXT 1530 SQ 30% 8 Apr 85 1:35p
"Name" is simply the name of the file.
"Length" is the unpacked file length. In other words, it is the
number of bytes of disk space which the file would take up if it were
extracted.
"Comp" is the compression method used on the entry. The following
compression methods are currently employed:
-- No compression.
Pack Runs of repeated byte values are collapsed.
SQ Huffman squeeze technique employed.
"SF" is the stowage factor. In other words, it is the percentage of
the file length which was saved by compression.
"Date" and "Time" are the date and time that the file had last been
modified at the time when it was added to the archive.
BACKUP RETENTION
================
When ARC adds or deletes archive entries it renames the original
archive to give it an extension of ".BAK", and then creates a new
archive with the desired changes. If you wish to retain this original
copy of the archive for backup purposes, then add the "B" (Backup)
command to your other commands.
For example, if you wanted to delete all entries with an extension of
".DOC" from an archive named "JUNK.ARC", but you wanted to keep a copy
around that still has them, then you could type:
ARC bd junk *.doc
or:
ARC db junk *.doc
MESSAGE SUPPRESION
==================
ARC prints two types of messages, warnings and comments.
Warnings are messages about suspected error conditions, such as when a
file to be extracted already exists, or when an extracted file fails
the CRC error check. Warnings may be suppressed by use of the "W"
(Warn) command. You should use this command sparingly. In fact, you
should probably not use this command at all.
Comments (or notes) are informative messages, such as naming each file
as it is added to the archive. Comments and notes may be suppressed
by use of the "N" (Note) command.
For example, suppose you extracted all files with an extension of
".BAS" from an archive named "JUNK.ARC" Then, after making some
changes which you decide not to keep, you decide that you want to
extract them all again, but you don't want to be asked to confirm
every one. In this case, you could type:
ARC xw junk *.bas
Or, if you are going to add a hundred files with an extension of
".MSG" to an archive named "TRASH.ARC", and you don't want ARC to list
them as it adds them, you could type:
ARC an trash *.msg
Or, if you want to extract the entire contents of an archive named
"JUNK.ARC", and you don't want to hear anything, then type:
ARC xnw junk
TESTING AN ARCHIVE
==================
The integrity of an archive may be tested by use of the "T" (Test)
command. This checks to make sure that all of the file headers are
properly placed, and that all of the files are in good shape.
This can be very useful for critical archives, where data integrity
must be assured. When an archive is tested, all of the entries in the
archive are unpacked (without saving them anywhere) so that a CRC
check value may be calculated and compared with the recorded CRC
value.
For example, if you just received an archive named "JUNK.ARC" over a
phone line, and you want to make sure that you received it properly,
you could type:
ARC t junk
It defeats the purpose of the T command to combine it with N or W.
SPECIAL NOTES
=============
Whenever ARC encounters a fatal error condition it leaves the original
archive on disk, renamed to have an extension of ".BAK" (backup).
The function used to calculate the CRC check value in previous
versions has been found to be in error. It has been replaced in
version 3.0 with a proper function. ARC will still read archives
created with earlier versions of ARC, but it will report a warning
that the CRC value is in error. All archives created prior to version
3.0 should be unpacked and repacked with the latest version of ARC.
Transmitting a file with XMODEM protocol rounds the size up to the
next multiple of 128 bytes, adding garbage to the end of the file.
This used to confuse ARC, causing it to think that the end of the
archive was invalidly formatted. This has been corrected in version
3.03. Older archives may still be read, but ARC may report them to be
improperly formatted. All files can be extracted, and no data is
lost. In addition, ARC will automatically correct the problem when it
is encountered.