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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.xenix,comp.unix.questions,comp.unix.wizards
Subject: Re: SysV echo
Message-ID: <17638@mimsy.UUCP>
Date: 20 May 89 06:03:36 GMT
References: <128@tdl.UUCP> <7170@bsu-cs.bsu.edu> <12970@ut-emx.UUCP> <541@visdc.UUCP>
Distribution: usa
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 63

In article <541@visdc.UUCP> jiii@visdc.UUCP (John E Van Deusen III) writes:
>For all purists who are almost certainly destined to be dragged into the
>SysV world kicking and screaming, let us formalize this solution as the
>command eucho.

I like it.  :-)

(Incidentally, V8 offers a solution, not particularly pretty, but it does
work.)

>Actually SysV echo does not munch all backslashes, only ones it finds
>to its liking; echo '\f\g\h' will output <ff>\g\h<cr>.  Is this
>unreasonable?

It is at least surprising (to one who knows C and other Unix languages).

>The shell, sh(1), also has an inconsistent appetite for back slashes.

Nay, not so:

>	foo=FOO
>	echo \$foo => $foo
>	echo `echo \$foo` => FOO
>
>In the second case the backslash was removed as a special treat, because
>the expression was contained within accents grave.

The shell is entirely consistent: one backslash is interpreted each
time an expression is evaluated.  Backquotes cause one additional
evaluation.  The sequence is in fact

0.	eval:		echo \$foo		(backslash quotes the $, so:)
1.	run:		echo $foo		(with output to pipe)
2.	output is: 	$foo
3.	splice output
4.	command is now:	echo $foo => FOO	(do variable substition)
5.	run:		echo FOO => FOO		(output to stdout now)
6.	output is:	FOO => FOO

To prevent this, you want step 3 to see output in step 2 of the
form `\$foo', which can be produced with

	eval `echo \\\$foo` => FOO

in 4BSD---this causes step 0 to see

	echo \\\$foo

which makes step 1 pass the argument

	\$foo

to echo.  If \$ is special in SysV echo (my guess now: it is not),
you will have to pass two backslashes to it rather than one---make
the argument `\\$foo'---which requires typing the command

	eval `echo \\\\\$foo` => FOO

If \$ is not special to a SysV echo, the BSDish version will work too.
(One hopes that at least \\ becomes \ in SysV echo.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris