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From: arnold@emory.uucp (Arnold D. Robbins {EUCC})
Newsgroups: comp.windows.misc
Subject: Re: Icons, pipes, etc.
Message-ID: <2187@emory.uucp>
Date: Fri, 31-Jul-87 17:18:54 EDT
Article-I.D.: emory.2187
Posted: Fri Jul 31 17:18:54 1987
Date-Received: Sun, 2-Aug-87 08:48:08 EDT
References: <8705190042.AA14664@cogsci.berkeley.edu> <9954@decwrl.DEC.COM> <66@laura.irb.informatik> <409@sugar.UUCP> <165@xyzzy.UUCP>
Reply-To: arnold@emory.UUCP (Arnold D. Robbins {EUCC})
Organization: Emory University Computing Center
Lines: 42

In article <165@xyzzy.UUCP> throopw@xyzzy.UUCP (Wayne A. Throop) writes:
>
>> peter@sugar.UUCP (Peter da Silva)
>> [...] you can describe some pipelines graphically that you would have a great
>> deal of trouble expressing on a command line.
>>
>> (awk)_______                                 _(one set of lines)
>>             \__(sort both together)|(grep2)_/
>> (sort|grep)_/                               \_(another set of lines)
>> 
>> Every now and then I come across something wierd like this I want to do.
>> I usually end up making temp files. Wasn't that the whole point of pipes
>> in the first place?
>
> [Wayne gives an involved solution using tee and multiple file descriptors.]

There exists a notation to do this in ksh-i, the latest version of ksh. To
use it though, your Unix must have the V8 /dev/fd  mechanism (keep an eye
on comp.sources.unix for a driver for 4.3 & NFS systems, from me, originally
from Fred Blonder). Anyway the notation is

	sort (awk) (sort | grep)

The ()'s enclose a shell pipeline, if preceded by a '<' or left alone,
the pipline's output is connected to a file in /dev/fd passed as the argument
to the program. The file will be the read end of a pipe, so sort would
see, e.g., "/dev/fd/4" and "/dev/fd/5" for its arguments, awk and the 
sort|grep pipeline would write on the other side of the pipe.

Such a pipeline may be written to as well:

	command | tee >(prog1) >(prog2)

would send command's output to both prog1 and prog2.

There is no existing Unix tool that corresponds to the 'grep2' in Peter's
example above.
-- 
Arnold Robbins
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