Re: Splitting string to array removes pipe symbol

[Vincent Stemen <zsh@hightek.org>]

On Tue, Dec 16, 2003 at 10:51:29AM +0000, Peter Stephenson wrote:
> Vincent Stemen wrote:
> > However, when the globsubst option is set, it removes the pipe '|'
> > symbol when it does the split.  Here is the trace output.
> > 
> >   +./t:62> cmd=uncompress foobar | cpio -i --quiet --unconditional
> >   +./t:63> cmd=( uncompress foobar cpio -i --quiet --unconditional )
> 
> You have null_glob (or maybe csh_null_glob) set.  `|' is split to a
> single bar.  Evaluation of the words takes place as if all the elements
> of the array are arguments, which is different from evaluating as a
> command.  (This is inevitable --- the only way of doing it differently
> would be to parse the line again completely from scratch after the
> glob_subst.)  In this case, the `|' is treated the same as (|),
> i.e. either nothing or nothing, and removed since nothing matches it.
> (You'd normally need the parentheses to stop it being evaluated as a
> pipe, but it can't be in an argument list.)
> 
> You can fix this particular problem by quoting,
>   cmd=("${(@)=cmd}")
> but only because that cancels the effect of glob_subst, so that `|' is
> just an ordinary character.  This may not be what you want.  It's
> likely to be very difficult to force the shell both to split a line into
> words *and* to parse it again as a full command line without joining it
> up again.
> 
> Most people would probably come up with something using `eval'.  What you
> should do depends why you need to split it at all.

I appreciate the quick reply.  You pinpointed exactly what the problem
was.  I did indeed have null_glob set.  I am learning to pay close
attention to the combination of options I have set when I get
unexpected behavior in Z shell scripts :-).

Putting quotes around the variable to be split did preserve the '|'
character.  However, I saw no difference in the result in this case
whether I used the (@) flag or did it with cmd=("${=cmd}").

The reason I was experimenting with splitting the line before
execution is because when I didn't, and ran "eval $cmd", I was getting
a null argument to eval.  Your reply pointed me in the right direction
to solve that mystery also :-).  I investigated further and found that
was also because of a null pattern expansion of the entire string.  My
final solution was to not split the string, use eval, and disable
glob_subst for the $cmd variable using "~~" (ie. eval ${~~cmd}).

Thank you very much for devoting your time to help.

- Vincent

-- 
Vincent Stemen
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