Ruby regex- does gsub store what it matches?

Question

If i use ``` .gsub(/matchthisregex/,"replace_with_this") ``` does gsub store what it matches with the regex somewhere? I'd like to use what it matches in my replacement string. For example something like ``` "replace_with_" + matchedregexstring + "this" ``` in my above example where the matchedregexstring would be the stored match from gsub? Sorry if that was confusing, I don't know how else to word that.

Accepted Answer

From the fine manual:

If replacement is a `String` it will be substituted for the matched text. It may contain back-references to the pattern’s capture groups of the form `\d`, where d is a group number, or `\k<n>`, where n is a group name. If it is a double-quoted string, both back-references must be preceded by an additional backslash. However, within replacement the special match variables, such as `&$`, will not refer to the current match. [...] In the block form, the current match string is passed in as a parameter, and variables such as `$1`, `$2`, $`, `$&`, and `$'` will be set appropriately. The value returned by the block will be substituted for the match on each call.

If you don't care about capture groups (i.e. things like `(expr)` in the regex) then you can use the block form and `$&`:

```
>> 'where is pancakes house?'.gsub(/is/) { "-#{$&}-" }
=> "where -is- pancakes house?"
```

If you do have capture groups then you can use `
` in the replacement string:

```
>> 'where is pancakes house?'.gsub(/(is)/, '-\1-')
=> "where -is- pancakes house?"
```

or `$n` in the block:

```
>> 'where is pancakes house?'.gsub(/(is)/) { "-#{$1}-" }
=> "where -is- pancakes house?"
```

Ruby regex- does gsub store what it matches?

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