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From: johnl@iecc.cambridge.ma.us (John R. Levine)
Newsgroups: comp.arch
Subject: Re: UNIX mind-set  -> OK, OK!
Message-ID: <9101141022.AA02013@iecc.cambridge.ma.us>
Date: 14 Jan 91 15:22:24 GMT
References: <1991Jan13.113349.21937@ims.alaska.edu> <11305@lanl.gov> <1991Jan14.013815.11419@ims.alaska.edu>
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Organization: I.E.C.C.
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In-Reply-To: <11314@lanl.gov>

In article <11314@lanl.gov> you write:
>Yes, both of the shells that are bundled with versions of UNIX _do_
>automatically trash (that is, 'process') the command line arguments to
>expand wildcards.  ... This is a choice that _should_ be left to the
>discretion of the utility writer.

Ah, finally an issue of software architecture appears in this argument.
The theory that the program rather than the command interpreter should
decide which arguments should be expanded and which ones shouldn't appears
plausible on the surface.  Having used both systems that do globbing in
the shell (various forms of Unix) and systems that do globbing in the
program (TOPS-10, Twenex and MS-DOS, among others, anyone else ever use
DOS-11?)

I can report that the Unix approach is far superior for several reasons:

Consistency: The Unix approach is easy to remember, all arguments are
expanded unless quoted.  On MS-DOS, some programs expand and some don't,
and you have to remember the rules for all of them.  The treatment of
environment variables is so confused that I don't even want to think about
it.  (Even Unix suffers here, my editor expands *foo arguments but not
$foo when reading file names interactively from the terminal.)

Simplicity: If programs do globbing, now each program has to have some way
to inhibit globbing for part or all of its filename arguments, so now you
have to put quoting facilities into every program or into the filenames
themselves.  The baroque VMS name syntax is an example of where this
leads.

Effectiveness: If I were the first programmer writing "echo" I might well
say to myself there's no need to expand these arguments, they're just text
strings.  In fact, one of the most common uses of Unix echo is to expand
file name patterns, something you can't do with MS-DOS echo for exactly
this reason.

Compatibility: When the file name syntax is extended, typically because of
a new kind of file system network facility, you only have to fix a few
programs, mostly the shells, to handle the new syntax.  On MS-DOS, there
are still programs that expand wild cards but only in the current
directory.  Twenex solved this problem by making globbing a system call,
but Twenex made everything else a system call, too, so that doesn't prove
much.  The Unix approach that has a system call to retrieve directory
entries but leaves all the rest of the string munging in the application
is a fair compromise.  One hopes that shared libraries will ameliorate
this kind of problem, but one doesn't bet a lot of money on it.

Regards,
John Levine, johnl@iecc.cambridge.ma.us, {spdcc|ima|world}!iecc!johnl