Using a lookup as suggested by Eliya and Jim but instead of using a regex capture it seems simpler to just split into individual characters and feed into a map doing a lookup in a ternary.

knoppix@Microknoppix:~$ perl -E '
> %esc = (
>    qq{\n} => q{\n},
>    qq{\r} => q{\r},
>    q{ } => q{\s},
>    );
> $str = qq{1\r\n 2 \n};
> say qq{Saw $_} for
>    map { exists $esc{ $_ } ? $esc{ $_ } : $_ }
>    split m{}, $str;'
Saw 1
Saw \r
Saw \n
Saw \s
Saw 2
Saw \s
Saw \n
knoppix@Microknoppix:~$
[download]

I hope this is helpful.