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From: dave.l@mac.com
Subject: Re: [9fans] late to the party - Here docs
Date: Wed,  7 Nov 2007 16:41:09 +0000
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Topicbox-Message-UUID: edcaec20-ead2-11e9-9d60-3106f5b1d025

>> I like here documents,

Metoo, although there may be a bias according to people's typical =20
application domains:
I often use them (on (l)unices) to spout the obscene gibberish that =20
some external system requires:

	mysql --blah-blah <<!
	select $blah blah;
	$imbibe_rat_urine
	...
	!

and it's a hell of a lot saner and simpler if it's all bottled up in =20
in one place,
rather than spread all over the script.

I may not use them frequently but when I do they are a brain-saver.


>> I think they look better than multi-line echoes

Exactly: they are an aesthetic convenience compared with multiple =20
echo invocations
but so are quotes compared with multiple backslashes.

>> though it is annoying they can't be used in fn definitions.

That's a bug which could be fixed ...


> i was thinking about this topic again the other day during an
> idle moment.  here documents are part of the parsing routine.
> but they don't end up in rc's machine language.

Does this mean they don't work in loops too?

Sadly, I have to nerdishly play sh's advocate:
I just tested a recent ksh and bash and, as expected, heredocs in =20
functions work,
as do things like:
	$ for n in 1 2 3 4 5;do cat<<EOF;done
	> $n
	> EOF
see below for why.

A quick scan of the rc source code suggests that rc won't DTRT with =20
an analogous construct:
can someone with a running plan9 or p9p please confirm this
as a matter of academic interest?

It's non-trivial (but not hard) to implement correctly:
the old Bourne shell, and thus, presumably, it's successors, DidTRT:
store the text of the here documents verbatim when they are parsed
then spit the substituted text into a (new) tempfile every time it's =20
needed.
IIRC it ate temporary files and there were also a few perverse =20
boundary cases where it would break or
lose track of it's temp files or leave them lying around, but so what?.

Trivial aside: sh also did `...` in here docs, as do it's successors.


> they really are anomolous critters.  they need to be taken out
> back and shot.  =E2=98=BA

Anomalous in use or in implementation?
Personally I think they are fine,
but their current implementation may need care and feeding.
If punishment is desired, may I suggest that the implementor be =20
castigated for anomalousness.

DaveL