#!/usr/bin/perl

use warnings;
use strict;
# use re "debug";

my %CSV = ('n' => 'n',
           't' => 't',
           'f' => 'f',
           '\\' => '\\',
          );


$_ = '\\\\\\\\\\';
print "$_\n";
my $pos = 0;
while (m/\\(.)/g) { $pos=pos($_);}
s/\\(.)/exists($CSV{$1}) ? "\\$1" : "\\\\$1"/ge;
s/^(.{$pos})\\$/$1\\\\/;

print "result:\n$_\n";