Capture group reference + numeral

Question

For example, I would like to replace a string by the first capture group, with a 1 appended to it.

I would like to do $11 (interpreted as $1 and 1), but this does not work on every flavour.

What should I do instead?

@rock321987 I'm using `.NET` flavour, but I would like to know the answer to as many flavours as possible. — Kenny Lau, Apr 29 '16 at 14:16
@Tushar I'm not sure if you have heard of it before, but [Retina](https://github.com/mbuettner/retina). — Kenny Lau, Apr 29 '16 at 14:16
@Tushar For your information, I come from [PPCG](http://codegolf.stackexchange.com). — Kenny Lau, Apr 29 '16 at 14:16
*Under the hood, it uses .NET's regex engine, which means that both the .NET flavour and the ECMAScript flavour are available* - Use `${1}1` to replace with the first backreference and `1`, use `${11}` to replace with the 11th backreference — Wiktor Stribiżew, Apr 29 '16 at 14:17
@WiktorStribiżew That's because Retina is a golfing language (esolang). — Kenny Lau, Apr 29 '16 at 14:26

score 3 · Accepted Answer · answered Apr 29 '16 at 14:28

The info at the Retina link you provided says:

Under the hood, it uses .NET's regex engine, which means that both the .NET flavour and the ECMAScript flavour are available.

So, if you are using the .NET flavor, use ${1}1 to replace with the first backreference and 1, use ${11} or $11 to replace with the 11th backreference.

If you are using an ECMAScript expression, $11 will be treated this way: if there are fewer than 11 capture groups, but there is 1, $1 will be parsed as the backreference to Group 1 followed with a literal 1; if there are 11 capture groups, it will be a backreference to the 11th group.

Capture group reference + numeral

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