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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.xenix,comp.unix.questions,comp.unix.wizards
Subject: SysV echo
Keywords: rm cat mv regexp
Message-ID: <17548@mimsy.UUCP>
Date: 16 May 89 22:58:31 GMT
References: <128@tdl.UUCP> <7170@bsu-cs.bsu.edu> <12970@ut-emx.UUCP> <536@visdc.UUCP>
Distribution: usa
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 44

In article <536@visdc.UUCP> jiii@visdc.UUCP (John E Van Deusen III) writes:
>Is there a particular SysV echo that is broken, or are you saying that
>System V echo is broken, in general, because, in your opinion, it should
>*not* do escape interpretation?

The latter.  (A separate program---printf(1)---should do escape
interpretation.)

The problem (which echo used to solve before it was changed in SysV or
SysIII [when *did* it acquire interpretation, anyway?]) is this:
suppose you are given a shell variable $foo, and need to echo it
uninterpreted?

There is a solution (albeit ugly):

	cat << end
	$foo
	end

but you may need to do something more.  To keep echo from munching away
backslashes, you might do this:

	qfoo=`cat << end | sed 's/\\\\/\\\\\\\\'
	$foo
	end`

except that, due to vagaries of Bourne's implementation, it does not work.
(It might work in ksh.)  So you get fancier:

	tf=${TMPDIR-/tmp}/quot$$; exec 3>$tf 4<$tf; rm $tf
	cat << end >&3
	$foo
	end
	qfoo=`sed 's/\\\\/\\\\\\\\/g' <&4`
	exec 3>&- 4<&-

and finally you have in $qfoo a version of $foo you can safely hand
to echo(1).  None of this would have been necessary if someone had
simply added printf(1) instead of mucking with echo(1).  Moreover, if
you might want to run your script on (e.g.) V7, you will need a
separate version without the extra quoting code.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris