[ruby-core:126850] [Ruby Bug#22381] MatchData assigned to $~ is incorrectly reused

25 Sep 2026


      Issue #22381 has been reported by jhawthorn (John Hawthorn).

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Bug #22381: MatchData assigned to $~ is incorrectly reused
https://bugs.ruby-lang.org/issues/22381

* Author: jhawthorn (John Hawthorn)
* Status: Open
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
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```ruby
m = /a/.match("a").dup # dup a MatchData (has no "busy" flag set)
$~ = m # assign to $~
/b/ =~ "b" # perform an 
p m
# "b" on Ruby 4.0 (and 1.8-2.7, incorrect)
# "a" on Ruby 3.0-3.4 (correct)
```

This is because the MATCH_BUSY flag isn't set correct and so the implicit match reuse (removed in #17507, re-added in #20652) mutates this escaped value


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