/[^\\]\\((\\)+\1)*$/

##</code><code>##

#!/usr/bin/perl -w

use strict;

my @split;
my $var;


# the original string that I want to split
my $tosplit = q(a=1&b=2\&3&c=4\\\\\&d=5);

# print out the string to confirm how many backslashes have been left
# by the quote statement
print $tosplit . "\n\n";

# Split the string on the ampersand
my @temp = split /&/, $tosplit;

# I thought this should have joined any two strings that were
# previously separated by an odd number of backslashes at the
# end of a string.

while ($_ = shift @temp) {
    $_ .= ("&" . shift @temp) and redo if /[^\\]\\((\\)+\1)*$/;
    push @split, $_;
};

foreach $var (@split) {print "$var" . "\n"};