#!/usr/bin/env perl

use strict;
use warnings;

my $search = 'C:\Dir1\Dir2\Dir3';
my $replace = '';

my $var = 'C:\Dir1\Dir2\Dir3\KeepMe';

$var =~ s/\Q$search/$replace/;

print "\$var[$var]\n";

##</code><code>##

ken@titan ~/tmp
$ perl -v

This is perl 5, version 36, subversion 0 (v5.36.0) built for cygwin-thread-multi
...

ken@titan ~/tmp
$ ./pm_11152209_re_backslashes.pl
$var[\KeepMe]

##</code><code>##

C:\cygwin64\home\ken\tmp>perl -v

This is perl 5, version 26, subversion 3 (v5.26.3) built for MSWin32-x64-multi-thread
...

C:\cygwin64\home\ken\tmp>perl pm_11152209_re_backslashes.pl
$var[\KeepMe]