while (<DATA>)
{
	# match any dollar followed by a number
	# of non whitespaces (unicode safe)
	# and replace it by then corresponding
	# environment variable
	
	if ( s/\$(\P{IsSpace}+)/$ENV{$1}/ )
	{
		$undefinedVars++ 
			unless $ENV{$1};
	}
	
	print;
}

if ( $undefinedVars > 0) 
{ 
	print "\n\nERROR: There were $undefinedVars undefined variables!\n"; 
}

__DATA__
bigcompany.product.part.path=$PATH
bigcompany.product.part.widgit=$WIDGIT
bigcompany.product.part.battery=$BATTERY
bigcompany.product.part.frobnicator=$FROBNICATOR