Redirecting variable fds

Redirecting variable fds

[Phil Pennock]

Okay, I'm stumped.  I'm trying to write a function which has as one of
its arguments a file-descriptor, which should be redirected to another
arg.  My attempt is:
function bar {
	DEBUGMEM_INFOFD=$1 LD_PRELOAD=./bar.so $argv[3,-1] $1>$2
}
bar 5 test.out some-command and-an-arg

Unfortunately, somewhere in parsing, the ``$1>$2'' bit expands out to
become ``5 > test.out'' which adds an extra arg and redirects stdout.

By quick-hack was to just shove it onto the input buffer:
function bar {
	print -z DEBUGMEM_INFOFD=$1 LD_PRELOAD=./bar.so $argv[3,-1] "$1>$2"
}
and then press return.  This is not exactly optimal.  What am I doing
wrong?  Is there something I'm missing or is this the best solution?

Thanks,
-- 
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Re: Redirecting variable fds

[Stefan Monnier]

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>>>>> "Phil" == Phil Pennock <phil@athenaeum.demon.co.uk> writes:
> function bar {
> 	DEBUGMEM_INFOFD=$1 LD_PRELOAD=./bar.so $argv[3,-1] $1>$2
> }

The parsing is done before the parameter expansion so you're screwed.
But there's a workaround, using eval:

	DEBUGMEM_INFOFD=$1 LD_PRELOAD=./bar.so eval $argv[3,-1] "$1>$2"

It's not quite correct in that the content of $argv[3,-1] should be escaped
to prevent its evaluation (à la "$@"), but my zsh expertise is lacking here.


	Stefan

Re: Redirecting variable fds

[Phil Pennock]

I may have stumbled across a bug.  I think the zsh-developers list might
be getting sick of my bug reports.

Typing away merrily, Stefan Monnier produced the immortal words:
> The parsing is done before the parameter expansion so you're screwed.
> But there's a workaround, using eval:
function bar {
> 	DEBUGMEM_INFOFD=$1 LD_PRELOAD=./bar.so eval $argv[3,-1] "$1>$2"
}
> It's not quite correct in that the content of $argv[3,-1] should be escaped
> to prevent its evaluation ( la "$@"), but my zsh expertise is lacking here.

Ah, thanks.

By the "$@" bit, it looks as though you're trying for "${(@)argv[3,-1}"
which doesn't on its own stop globbing.  I've handled that by changing
the 'eval ' for 'eval noglob '.  So now quoted args behave as expected
and unquoted ones are expanded at function-call time.

The problem is that DEBUGMEM_INFO and LD_PRELOAD don't actually make it
into the environment.  Using 'env' as the command passed through, I can
see quite plainly that they aren't there.  But using env to place the
values into the environment works:
function bar {
  eval noglob env DEBUGMEM_INFOFD=$1 LD_PRELOAD=./bar.so "${(@)argv[3,-1]} "$1>$2"
}

Trying this:
% FOO=x eval sh -c 'echo $FOO'
and then without the eval, it seems the eval loses the auto-export
functionality, in both 3.0.5 and 3.1.5.  It doesn't appear to be
documented though.

Bug?
-- 
--> Phil Pennock ; GAT d- s+:+ a22 C++(++++) UL++++/I+++/S+++/H+ P++@ L+++
E-@ W(+) N>++ o !K w--- O>+ M V !PS PE Y+ PGP+ t-- 5++ X+ R !tv b++>+++ DI+ D+
G+ e+ h* r y?