my $file = 'c:\folder1\filename.doc';

$file =~ s{         # Substitue...
            \\          # a backslash
            [^\\]*      # zero or more not-backslashes
            $           # at the end of string
          }
          {}x;      # with nothing
                    #     allow comments & spaces in search-pattern

print $file; # c:\folder1