a="["6000208900","600020890225","600900231930"]"
#expected result [6000208900,600020890225,600900231930]

a.gsub!(/^"|"?$/, '')

a = "["6000208902912790"]"
puts a # => ["6000208902912790"]

irb(main):001:0> require 'json'
=> true
irb(main):002:0> a = "["6000208902912790"]"
=> "["6000208902912790"]"
irb(main):003:0> b = JSON.parse a
=> ["6000208902912790"]
irb(main):004:0> b
=> ["6000208902912790"]
irb(main):005:0> b.to_s
=> "["6000208902912790"]"

irb(main):002:0> a = "["6000208900","600020890225","600900231930"]"
=> "["6000208900","600020890225","600900231930"]"
irb(main):006:0> a.scan(/d+/).map(&:to_i)
=> [6000208900, 600020890225, 600900231930]
irb(main):007:0>

a.gsub(/((?<=^[)")|("(?=]$))/, '')

=> a = "["6000208902912790"]"
=> a.chars.select{ |x| x =~ %r|d| }.join
=> "6000208902912790"
=> [a.chars.select { |x| x =~ %r|d| }.join]
=> ["6000208902912790"] # <= array with string
=> [a.chars.select { |x| x =~ %r|d| }.join].to_s
=> "["6000208902912790"]" # <= come back :)

a="["6000208902912790"]" will return  `unexpected tINTEGER`error;

a.gsub!(/"/, '')

content = "[{"addon_id":"1","addon_price":"5"}]"
# OUTPUT at Console => "[{"addon_id":"1","addon_price":"5"}]"

JSON.parse(content.gsub('"', '"'))
# OUTPUT at Console => [{"addon_id"=>"1", "addon_price"=>"5"}]