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To: The rc user community <rc@archone.tamu.edu>
Subject: Re: A lighter read function 
In-reply-to: david's message of Wed, 11 Dec 91 07:28:26 -0500.
             <22832.692454506@golem.UUCP> 
Date: Wed, 11 Dec 1991 13:28:23 -0600
From: Chris Siebenmann <cks@hawkwind.utcs.toronto.edu>
Message-Id: <91Dec11.142829est.2716@hawkwind.utcs.toronto.edu>

 This has come up before on the mailing list. One cannot use sed, awk,
or handgrown alternatives that use stdio when you are not reading from
a terminal, because their buffering will eat too much of the input
stream and then silently discard it when they exit. You can convince
yourself by defining read in terms of one of them and then doing:
	{echo A; echo B} | {read a; echo a $a; read b; echo b $b}
and noticing what comes out.

 line is safe, and trivial to write; I will happily mail my version
to anyone who wants it. It even comes with a manual page.

 Here is my current version of read along with a couple of functions
that it relies on:

# 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}
	if (! ~ $_v(2) 0) return $_v(2);
	_v=`{echo $_v(1)}
	for (_i in $*) {
		$_i=$_v(1); sshift _v 1
	}
	$_i=($$_i $_v)
}; return 0; }

# 'supershift' function for rc.
# usage:
#	sshift varname
#	sshift varname number
# shifts the list varname by number (default 1) positions.
fn sshift { if (~ $#* 1 ) { _sshift $1 1 $$1 } else { _sshift $1 $2 $$1 } }

# this function does most of the work.
# _sshift NAME COUNT LISTELEMS
# shift LISTELEMS COUNT items left, and assign the result to NAME.
fn _sshift { _vn=() { _vn=$1; shift; shift $1; shift; $_vn=$* } }

	- cks