Issue #12636 has been reported by Mike McFadden.

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Bug #12636: string.gsub(/([a-z](?=[A-Z._ ]))/, "#{$1} ") returns wrong result (possible C-string leak?)
https://bugs.ruby-lang.org/issues/12636

* Author: Mike McFadden
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin15]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
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Verified in Ruby 2.1, 2.2, and 2.3.

    > "Hello.World".gsub(/([a-z](?=[A-Z._ ]))/, "#{$1} ")
    => "Hell .World"

^ wrong answer; it should be `"Hello .World"`

    > "Hello.World".gsub(/([a-z](?=[A-Z._ ]))/, "#{$1} ")
    => "Hello .World"

^ running it a second time in the same IRB session now returns the correct result, however...

    > "Help.World".gsub(/([a-z](?=[A-Z._ ]))/, "#{$1} ")
    => "Helo .World"

^ now the p turned into an o somehow? It's clearly retaining strings from the previous invocation and reusing them, but not updating every byte.



Here's the equivalent code in JavaScript, which returns the correct result every time:

    "Hello.World".replace(/([a-z](?=[A-Z._ ]))/g, "$1 ")




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