G'day FFSparky,

You seem to have a number of problems.

• Don't use interpolating double-quotes and then try to manually escape characters within the quoted string (e.g. "C:\\Dir1\\Dir2\\Dir3"); it's tedious, fiddly and error-prone. Instead, use non-interpolating single-quotes and don't make any manual modifications (e.g. 'C:\Dir1\Dir2\Dir3').
• The $search part of s/$search/$replace/ interpolates. Let Perl escape characters here with quotemeta: s/\Q$search/$replace/. Note that you're still not doing tedious, fiddly and error-prone manual modifications.
• The '/eeg' modifiers on the s/// are completely unnecessary. See "perlre: Modifiers" and "perlop: Regexp Quote-Like Operators: s/PATTERN/REPLACEMENT/msixpodualngcer".

Consider this example script (pm_11152209_re_backslashes.pl) which is portable:

#!/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";
[download]

On Cygwin:

ken@titan ~/tmp
$ perl -v

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

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

On Win10:

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

This is perl 5, version 26, subversion 3 (v5.26.3) built for MSWin32-x
+64-multi-thread
...

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