johngg@aleatico:~$ perl -Mstrict -Mwarnings -E 'say q{};
my( $path ) = qw{ C:\Users\fred\file.txt };
say $path;
$path =~ s{\x5c}{/}g;
say $path;'

C:\Users\fred\file.txt
C:/Users/fred/file.txt

##</code><code>##

johngg@aleatico:~$ perl -Mstrict -Mwarnings -E 'say q{};
my( $path ) = qw{ C:\Users\fred\file.txt };
say $path;
$path =~ s{(?=\x5c)}{ chr 92 }eg;
say $path;'

C:\Users\fred\file.txt
C:\\Users\\fred\\file.txt