$r = $1 ? \$$r->{$1} : \$$r->[$2]
       while $string =~ /\G(?:\.?(\w+)|\[(\d+)\])/g;
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Note - I'm assuming that the input is known to be valid and that $1 can never be '0'.

Given I'm already assuming $string is well formed the regex is much more complex than it needs to be.

    $r = $1 ? \$$r->{$1} : \$$r->[$2]
       while $string =~ /(\w+)|\[(\d+)/g;
[download]