Two esoteric zsh questions

Two esoteric zsh questions

[Jerry Peek]

(Is *any* zsh question esoteric?  Or are *all* zsh questions? ;-)
Here's a question that might be a bug, then a follow-up "how to".
I'm using 3.0.7 on Linux (Red Hat 6.2) right now.

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1) Can anyone explain the difference in the following two cases?  The
first sets a shell variable; the second sets an environment variable.
In the second, I have to quote the `who`:

	% whoson=`who`
	%

	% export WHOSON=`who`
	zsh: not an identifier: 06:56
	% export WHOSON="`who`"
	%

(The first line of the "who" output ends with 06:56.)

I looked through the FAQ and scanned through a change list... but
didn't spot changes in more recent versions, so I'm asking the list.
Is the difference a bug, side effect, or feature?

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2) I wanted to compare the values of $whoson and $WHOSON.  I couldn't
think of a way to use two <<< operators, so I tried this kludge:

	% diff - <(echo $WHOSON) <<<$whoson
	%

Does anyone know a cleaner way to do that?

[BTW, this next mess wasn't as simple but it worked fine too:

	% diff - <(cat <<<$WHOSON) <<<$whoson

zsh is amazing...]

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Thanks!

--Jerry Peek, jpeek@jpeek.com
  http://www.jpeek.com/

PS: I mentioned last spring that the third edition of Unix Power Tools
will cover zsh -- and asked if the new shell would be ready by August
so we could put it on the book's CD-ROM.  FYI, due to some scheduling
problems, I'm still working on the book; the target date is early 2001.)

Re: Two esoteric zsh questions

[Zefram]

Jerry Peek wrote:
>1) Can anyone explain the difference in the following two cases?  The
>first sets a shell variable; the second sets an environment variable.
>In the second, I have to quote the `who`:
>
>	% whoson=`who`
>	% export WHOSON=`who`
>
>I looked through the FAQ and scanned through a change list... but
>didn't spot changes in more recent versions, so I'm asking the list.
>Is the difference a bug, side effect, or feature?

Side effect of the way `export' is defined.  These two commands use
completely different bits of shell grammar.  The first is a variable
assignment, in which field splitting is not performed -- everything
in the word on the RHS of the = is assigned to the variable named.
The second is a simple command; the first word is `export' and the
second is `WHOSON=`who`'.  In the expansion of that second word, the
backquoted section is subjected to field splitting (I think `` and
$() are the only places where zsh does field splitting by default),
which results in a simple command with more than just the two words.
The `export' command looks at each argument in turn and tries to make
an assignment out of it; its second and subsequent arguments in this
case are part of the output of who.

-zefram

Re: Two esoteric zsh questions

[Bart Schaefer]

On Sep 5,  1:21pm, Jerry Peek wrote:
>
> (Is *any* zsh question esoteric?  Or are *all* zsh questions? ;-)

Both.

> 1) Can anyone explain the difference in the following two cases?  The
> first sets a shell variable; the second sets an environment variable.

Zefram answered this.

> 2) I wanted to compare the values of $whoson and $WHOSON.

You mean you wanted to see the differences, not just know whether there
are differences?  When I hear "compare the values" I think of

	[[ $whoson == $WHOSON ]]

> I couldn't think of a way to use two <<< operators

Right; if you did so, multios would concatenate the two inputs.

> 	% diff - <(echo $WHOSON) <<<$whoson
> 	%
> 
> Does anyone know a cleaner way to do that?

Aside from using "print -r --" in place of "echo", so that backslashes or
leading hyphens in $WHOSON won't cause problems, the only thing that comes
to mind is

	diff <(<<<$whoson) <(<<<$WHOSON)

which is really mostly same as

> 	% diff - <(cat <<<$WHOSON) <<<$whoson

except that zsh implements the "cat" internally, and you can give the args
in the same order that they'll appear in the diff output, which is slightly
more understandable.