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From: GHGAQZ4@cc1.kuleuven.ac.be
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: Script bits
Message-ID: <91050.162708GHGAQZ4@cc1.kuleuven.ac.be>
Date: 19 Feb 91 16:26:08 GMT
References: <18ac1a05.ARN2ae4@prolix.pub.uu.oz.au> <8660@gollum.twg.com>
Organization: K.U.Leuven - Academic Computing Center
Lines: 43

>Oops.. just realized my post earlier was incomplete.
>
>There is very little "parsing" to do to recognize what kind of
>executable you have there.  At least on Unix what is done is make
>the first 2 (4?) bytes be a "magic number".  For an executable
>script the magic number is "#!" and for normal object files the
>magic number is something that cannot appear in normal text.  Hmm..
>this assumption will likely break soon since Unix is being
>internationalized, part of which is support for 8-bit text.  Sigh..
>
>Yeah, sure, I'm being inflamatory by saying "Unix does this already"
>.. but, really, the capabilities are there and would be a useful
>addition to AmigaDOS.
>
>For instance Unix has different sorts of "object files" with
>different capabilities -- simply by using different Magic Numbers.
>Using a Unix-y magic number scheme the "pure" bit in the protection
>is not necessary, it would just be a different magic number.  After
>all, what does the purity of the program have to do with file
>protections?  Methinks it was just a handy place to stuff a bit
>without having to change too many things.  (quick hack)
>
>If you wanna do a one-up-manship with Unix then I suggest putting
>the Magic Number some other place besides the beginning of the file.
>
>
>        David

You obviously don't know the Amiga well. Amiga executables are very
well recognizable by the first 4 bytes of the file. These 4 bytes
are always equal to 0x000003F8 (or something like that). This is
a highly unlikely longword for ascii files.

I think I'd rather have a pure bit than another keyword in the file
to indicate it is pure. With the pure bit you do not have to open
the file to see if it is pure. A simple Lock will suffice.
Opening a file has much more overhead than locking the file.
Having a pure bit means that you can include this bit in the directory
listing. If there was a Magic Number IN the file, the directory utility
would have to open the file, read some bytes from it and close the file
again, and this for EACH file in the directory.

            Jorrit Tyberghein