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From:	culliton@srg.af.mil (Tom Culliton x2278)
X-Mailer: SCO System V Mail (version 3.2)
To:	cks@hawkwind.utcs.toronto.edu, rc@hawkwind.utcs.toronto.edu
Subject: Re: Another little challenge
Date:	Thu, 25 Jun 1992 20:31:25 -0400
Message-Id: <9206252031.aa11853@ceres.srg.af.mil>

Excellent!  It struck me that there had to be an elegant solution but I
just couldn't see it.  That little gem is already in my .rcrc file. :-)

My recent rash of questions is prompted by converting a friend to rc
and helping him solve the problems encountered.  The other thing that
reared it's head was the old "everything is exported" problem.  Rich
produced a partial solution back in May, but it required that you
explicitly "unexport" things.  I'm currently tinkering with a solution
that looks like this:

# This code can be fooled by really pathological cases involving embedded
# newlines followed by either 'fn ' or '='.  Fixing this is left as an
# exercise for the reader. ;-)  It's already slow enough for me.

exported=()
fn export { exported=($exported $*) }

fn fns_n_vars { i=() tmp=() {
	fn_list=()
	var_list=()
	for (i in `` ($nl) {whatis})
		if (~ $i 'fn '*) {
			tmp=`{echo $i}
			fn_list=($fn_list $tmp(2))
		} else if (~ $i *'='*) {
			tmp=`` ('=') {echo $i}
			var_list=($var_list $tmp(1))
		}
}}
fns_n_vars	# pre-load should be done after all variable setting in .rcrc

# Stuff run by clean_env will only see the exported variables.  You can
# also give this function multiple names for programs that choke on big
# env's.  Note that keeping fn_list and var_list up to date needs to be
# improved.  I thought about something like:
#	x=`` ($nl) {whatis} if (! ~ $#x $xcnt) { xcnt=$#x; fns_n_vars }
# but it could be fooled pretty easily.  Ideas?

fn clean_env { i=() @{
	if (~ $#fn_list 0 && ~ $#var_list 0) {
		fns_n_vars
	}
	for (i in $fn_list) {
		eval 'fn '^$i
	}
	for (i in $var_list) {
		if (! ~ $i $exported i exported) {
			eval $i^'=()'
		}
	}
	i=(); fn_list=(); var_list=(); exported=(); fn clean_env

	if (~ $0 clean_env)
		exec $*
	else
		exec $0 $*
}}