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Text File | 1985-05-06 | 11KB | 321 lines

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.