From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
Subject: Re: [9fans] dumb question
From: rog@vitanuova.com
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Date: Fri, 28 Jun 2002 15:08:02 +0100
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>  From time to time I toy with the idea of implementing a
> fully correct xargs (the Unix one doesn't quote arguments).

if you're guaranteed not to have spaces or newlines in filenames, then
it doesn't matter.

i have a small C xargs (attached) that is probably still correct.  (i
think newlines are probably still banned in filenames).

> I wonder if structural r.e.s can express a
> complete and correct quoting algorithm.

well a normal r.e.  can express the rc quoting algorithm.  the problem
you can't just match it, you've got to translate it as well.

(([^ \t']+)|'([^']|\n|'')*')

the inferno shell provides primitives for quoting and unquoting lists,
which are useful at times.  (e.g.  variables in /env are stored in
quoted form rather than '\0' terminated).

> what we really need is a convenient way to feed macros to
> sam in a sed-like manner and somebody with the time and
> inclination to develop suitable macros and package it all up.

to be honest there's very little that beats the convenience of:

	rm `{ls | grep -v precious}

(which is now broken).

while i'm mentioning the inferno shell, nemo's example works nicely,
as you can pass shell fragments around as words.

e.g.
	walk /source {if {ftest -r $1} {echo $1}}

which lets the shell parse the argument command before passing it on
to the walk script:

	#!/dis/sh
	if {! ~ $#* 2} {
		echo 'usage: walk file cmd' >[1=2]
		exit usage
	}
	(file cmd)=$*
	du -a $file | getlines {
		(nil f) := ${split ' ' $line}
		$cmd $f
	}

if du produced a quoted word for the filename,

	(nil f) := ${split ' ' $line}

would just change to:

	(nil f) := ${unquote ' ' $line}

it's quite nice being able to do this sort of thing, but there are
tradeoffs, naturally.

  cheers,
    rog.


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