#!/usr/bin/perl -w
sub trace { print join(' ', map { defined($_) ? $_ : '#undef#' } @_), "\n"; }

my $val;
trace('Before first chunk, value is', $val);

$val='foobar';
trace('Before second chunk, value is', $val);

$val=7.3;
trace('Final value is', $val);

##</code><code>##

roboticus@swill $ ./foo.pl
Before first chunk, value is #undef#
Before second chunk, value is foobar
Final value is 7.3