Amiga Computing - Commodore Is Awesome

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Looking for on easy way to organise backup operations?: Paul Overaa shows you how On many platforms, including the PC, REXX (the language upon which ARexx is based) is used primarily as a ^^^ macro language for system house keeping operations. Moving and renaming sets of files, batch editing of text files, performing stan dardised backup operations and so on. This system-oriented use is perfectly under standable on these other platforms since the operating system is, to a large extent, the only other 'process' that can be communicated with. ARexx of course, has no such restrictions and in this sense Amiga users are extremely fortunate. ARexx's ability to communicate easily with other programs does tend to result however, in the potentially useful batch processing links with AmigaDOS, often taking a back seat Now this is clearly a shame because for these types of appli cations, ARexx is far more powerful than AmigaDOS's own scripting language and you need look no further than the rather neglected area of data backup to realise the possibilities. Whilst data safety is obviously the primary con cern, the objective of any type of backup arrange ments ought really to be to get some sort of sys tem going which makes routine data backup as easy as possible. It is, after all, a well known fact that procedures which are awkward tend not to get followed. Fortunately for most users, backing up a com plete high-capacity hard disk on a regular basis is almost never necessary. For example, programs themselves, once backup copies of the master disks have been made, do not need further regu lar backing up. The unwritten rule with data files of course is that you back up files only as fre quently as they change. The key to success is organisation. Make sure you have appropriate directory structures and/or hard disk partitioning (ie the creation of a number of different logical drives). One big help is to make sure you keep data files separate from the applica tions programs which create and use them. Within this highest level division of programs versus data, the next most useful hierarchy criteria is the required file backup frequency. If, for exam ple, an order file is backed up once a day, it is worth keeping that data in a directory (or hard disk partition) that contains only those files that need to be backed up with this frequency. An ARexx Example Once you have a workable backup plan available ARexx can, in most cases, completely eliminate the need for using dedicated backup utilities. Let's say, for instance, you're interested in automating the backup of a directory called 'daily' that exists on a partition called Work. In short you want to copy, to floppy disk, any files present in that direc tory whose contents have changed since the With a little organisation, plus some help from ARexx, almost all backup operations can become a piece of cake! /* backup.ren */ TEHP='fiaa:T/te»pl BACKUPJ£ST='dfO:daily' A«CHlVEjn='ar drawer was last backed up. The trick here is to adopt the same method as used by most archiving utilities. Whenever a file is backed up the archive bit of the source file gets set If, when the next backup is performed, that bit is still set the file hasn't changed and does not need recopying to your backup disk. As far as doing this type of thing via ARexx is concerned the important first step is identifying the names of the files present in the chosen source directory. ARexx's address command can be used in conjunction with AmigaDOS's LIST command to generate just such a list. One approach is to set up a couple of constant definitions to point to the source directory and to a temporary file for storing the list command out put. The files, nodates and nohead switches inci- address cowaitd 'list' BACKUPJOURCE 'to' TEMP 'file; nodates nohead' if Opentfh,TEHP,'r'> then do do uhile "EOF(fli) Une=Readlri(fb) if Length(Line)>0 then do parss var line file date flags if PosURCHIVE BIT,flags)=O then end do fi Le=BACKUP_SOURCE j|fi Le say 'Batting up...' file address coanand 'copy >NIL:' file 'to' BACKJPJEST address cossand ■protect >HIL:' file '+a add1 end end call Closc(fh) address comnd 'delete >HIL:' TENP say 'Operations conplete!' enc dentally can be used on the LIST command line to ensure that only the file names, size and protec tion flags values are sent to the output file. ARexx code such as... BAC«:UP_SIJUSCE=1«ort:daiLy/1 TENP='Hai:t/teip' address conarancE 'list' BACKUPJOURCE 'to' TEUP 'files Itodatss "ahead1 therefore ends up generating a temporary file con sisting of text lines whose general format is... , By reading these lines and splitting them into individual name, size and protection flag values using the ARexx PARSE instruction it's then easy enough to check each flag set to see whether the archive bit is clear or not Any file whose archive bit is not set represents a file that has been altered since the last backup, so all we need to do is copy all such files to the destination backup directory - resetting the archive bits of each source file as we do so. Now your individual requirements for backup are doubtless going to be different from mine but the example shown in listing 1 should give a rea sonable starting point for creating your own back up scripts. In this case it's the general ideas that are the important thing - so the thing to do is to set up some dummy source/destination directo ries on your own system (modifying the script's directory references to suit) and then experiment. Once you see how these archive bit arrangements work you should then be easily able to incorpo rate similar ideas into your own backup arrange ments! Listing 1: A typical archive bit based ARexx backing up script. Notice how the >NIL: statement is used to discard output from the copy, protect and delete commands'. Amiga Computing MARCH 1997
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Amiga Computing - Commodore Is Awesome

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