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From: jlg@lanl.gov (Jim Giles)
Newsgroups: comp.os.misc
Subject: Re: Globbing
Message-ID: <17097@lanl.gov>
Date: 8 Mar 91 19:33:32 GMT
References: <EIY96WH@xds13.ferranti.com>
Distribution: na
Organization: Los Alamos Natl Lab, Los Alamos, N.M.
Lines: 54

From article <EIY96WH@xds13.ferranti.com>, by peter@ficc.ferranti.com (Peter da Silva):
> In article <KENW.91Mar6231308@skyler.arc.ab.ca> kenw@skyler.arc.ab.ca (Ken Wallewein) writes:
>>   Peter, you asked me to come up with other examples besides the mv/rename
>> one. [...] It wasn't easy; they don't exist now, as far as I know -- maybe
>> due to a chicken-and-egg precedence problem
> 
> Look for examples on VMS, DOS, AmigaDOS, etc. No catch-22 there.


It's not hard to come up with enormous numbers of examples where the
command language would be better if globbing were not done automatically
by the shell.  All you have to do is look at the assumptions that the
shell is making when it automatically globs and consider cases that
violate such assumptions.

1) The case everyone thought of first: you want globbing to produce
   _two_ distinct lists that correspond.  This is the mv/rename
   example that everyone has been discussing.

2) You want an argument globbed, but _not_ in the context of the
   local filespace.  For example, suppose you have an external
   mass storage device that you periodically save files from your
   local filesystem to or periodically load data from.  You might
   want the syntax to look like "save <pattern>" and "get <pattern>".
   But, you can't do this if the shell automatically globs because
   the <pattern> is always globbed in the _local_ filespace - but
   for the 'get' command, you want it to be globbed in the context
   of the external filesystem.  With the increasing importance of
   distributed processing, the ability to glob file arguments in
   _non-local_ contexts may be very valuable.

3) You want the argument globbed, but _not_ in the context of a
   filespace at all.  After all, globbing is just a pattern matching
   facility - there are any number of lists of data which could
   benefit from making such a pattern match available for them.
   For example, you could have a version of 'ls' which allowed
   globbing on the owner or group fields: "ls -l *.p -group c-*"
   would list all '.p' files which are owned by someone in 'c'
   division (according to our naming convention for groups).

It is no trick to come up with numerous examples of globbing that fit
each of these three categories - or more than one at a time!  For
example, you may want one argument globbed as an account number and
another argument to generate a corresponding list of (say) mail
addresses based on the matched part of the account - a mix of
categories (1) and (3) above.

Note also that quoting and escape characters are _not_ sufficient to
perform the above functionalities in the present 'automatic glob'
environments.  Quoting is supposed to prevent an argument from
being globbed - but you _want_ all these arguments to be globbed,
it's just that you want it done in a different context.

J. Giles