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To: Chris Siebenmann <cks@hawkwind.utcs.toronto.edu>
cc: The rc user community <rc@archone.tamu.edu>
Subject: Re: A lighter read function 
In-reply-to: Your message of "Wed, 11 Dec 91 14:28:23 EST."
             <91Dec11.142829est.2716@hawkwind.utcs.toronto.edu> 
Date: Thu, 12 Dec 1991 18:58:56 -0600
Message-ID: <26539.692585936@golem.UUCP>
From: "David J. Fiander" <david@golem.uucp>

>From: 	Chris Siebenmann <hawkwind.utcs.toronto.edu!cks@rutgers.uucp>
> Here is my current version of read along with a couple of functions
>that it relies on:

It looks pretty good.

>
># A real read function, as in 'read var var var'. Returns failure
># on EOF.  relies on the 'line' program.
>nl='
>'
>fn read { _v=() _i=() {
>	_v=`` $nl {line; echo $status}

This is why byron added the "``ifs{}" extension, but the Plan 9
way is probably

	ifs=$nl { _v=`{line; echo $status}}

which sets ifs for only the one command, but sets _v globally.

>	if (! ~ $_v(2) 0) return $_v(2);

There's a small problem with this.  If line sees an EOF, then
it will print a newline, and exit with status 1.  _v is thus
set to "1", since there is nothing before the first nl.  There
is no $_v(2), so the ~ fails, and read returns success.

I got around this by writing it as:

	x = `{line || echo 1^$nl^1; echo 0}

Then, if line fails, we get

	x = (1 1)

 otherwise we get

	x = ('the line' 0)

--
David J. Fiander   |email [Fr., = enamel] Used attrib. in `email ink', ink
<david@golem.uucp> |used on glass, porcelain, etc.