Neither did you show actual Perl code, nor did you describe how it did not work for you. This will perform the substitution you requested:

use strict;
use warnings;

my $path = 'c:\abc\xyz';
$path =~ s/\\/\\\\/g;
print $path;

__END__

c:\\abc\\xyz
[download]

The double quotes interpolate. If you use strict and warnings, you will get a warning message.

On a side note, when posting, just include code within code tags, not all of your text.