From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from oldp.astro.wisc.edu ([128.104.39.15]) by hawkwind.utcs.toronto.edu with SMTP id <2701>; Thu, 17 Dec 1992 04:00:33 -0500
Received: by oldp.astro.wisc.edu (5.65/DEC-Ultrix/4.3)
	id AA17826; Thu, 17 Dec 1992 03:00:18 -0600
Message-Id: <9212170900.AA17826@oldp.astro.wisc.edu>
To:	rc@hawkwind.utcs.toronto.edu
Subject: Here documents
Date:	Thu, 17 Dec 1992 04:00:18 -0500
From:	Alan Watson <alan@oldp.astro.wisc.edu>
X-Mts: smtp

I was playing around with here documents, trying to get environment
variable substitution within a file, when I noticed the following:

[1]	; foo=bar
	; cat <<EOF
	foo
	EOF
	bar
	;

but if I try:

[2]	; { echo '$foo' ; echo EOF } | cat <<EOF

then rc ignores the pipe and attempts to read from the terminal.  This
is all well and good, as the rc manual page states:

       ``Here documents'' are supported as in sh with the use of

	  command << 'eof-marker'

and my man page for sh (under Ultrix 4.3: hardly definitive) states:

     <<word
	  The shell input is read up to	a line the same	as word, or end of
	  file.	 The resulting document	becomes	the standard input.  

and one can argue that the `shell input' is not the same as the
standard input to the cat command.  However, the following is more
interesting:

[3]	; { echo '$foo' ; echo EOF } | rc -c 'cat <<EOF'
	line 1: heredoc incomplete near EOF

Clearly, the `shell command input' is the string `cat <<EOF', but is
this the same as the `shell input'?  The following code achieves my
purpose:

[4]	; { echo 'cat <<EOF' ; echo '$foo' ; echo EOF } | rc

I now have several questions:

	1. Can someone provide a more definitive definition of the
	source of here documents.

	2. Should a here document be read from rc's stdin, rather than the
	source of its commands?  Would this break any existing scripts?  
	This would allow example [3] to work.

	3. Should a here document be read from a command's stdin,
	rather than the shell input?  Would this break any existing scripts?
	This would allow example [2] to work.

Perhaps the answers are obvious and of no interest to anyone else, but
I am intrigued that such subtleties exist in an apparently
straightforward feature of the language.

Alan Watson.