```ruby
require 'benchmark/ips'

Benchmark.ips do |x|
  x.report("$&") {
    "foo".sub(/f/) { $&.upcase }
  }
  x.report("block var") {
    "foo".sub(/f/) {|match| match.upcase }
  }
end

```

```
Calculating -------------------------------------
                  $&    48.658k i/100ms
           block var    49.666k i/100ms
-------------------------------------------------
                  $&    873.156k (± 9.3%) i/s -      4.331M
           block var    969.744k (± 9.2%) i/s -      4.818M
```

It's faster, and gets rid of a few "magic" global variables