Question: ```
string = "Jack and Jill went up the hill to fetch a pail of water. Jack fell down and broke his crown. And Jill came tumbling after. "
d = string.match(/(jack|jill)/i) # -> MatchData "Jill" 1:"Jill"
d.size # -> 1

```

This only match the first occurrence it seems.  

`string.scan` does the job partially but it doesn't tell anything about the index of the matched pattern.

How do i get a list of all the matched instances of the pattern and their indices (positions)?

Answer: 
You can use `.scan` and `$`` global variable, which means *The string to the left of the last successful match*, but it doesn't work inside usual `.scan`, so you need this *hack* (stolen from [this answer](https://stackoverflow.com/a/2257073/322020)):

```ruby
string = "Jack and Jill went up the hill to fetch a pail of water. Jack fell down and broke his crown. And Jill came tumbling after. "  
string.to_enum(:scan, /(jack|jill)/i).map do |m,|
  p [$`.size, m]
end

```

output:

```
[0, "Jack"]
[9, "Jill"]
[57, "Jack"]
[97, "Jill"]

```

**UPD:**

Note the behaviour of lookbehind – you get the index of the really matched part, not the *look* one:

```none
irb> "ab".to_enum(:scan, /ab/     ).map{ |m,| [$`.size, $~.begin(0), m] }
=> [[0, 0, "ab"]]
irb> "ab".to_enum(:scan, /(?<=a)b/).map{ |m,| [$`.size, $~.begin(0), m] }
=> [[1, 1, "b"]]

```
Here's a modification of Nakilon's answer if you want to put just the locations of "Jack" into an array

```
location_array = Array.new

string = "Jack and Jack went up the hill to fetch a pail of Jack..."  
string.to_enum(:scan,/(jack)/i).map do |m,|
    location_array.push [$`.size]
end

```