Issue #7787 has been reported by calfeld (Christopher Alfeld). ---------------------------------------- Bug #7787: ruby 1.9 regexp quantifiers behave unpredictably when stacked https://bugs.ruby-lang.org/issues/7787 Author: calfeld (Christopher Alfeld) Status: Open Priority: Normal Assignee: Category: Target version: ruby -v: ruby 1.9.3p327 (2012-11-10 revision 37606) [x86_64-darwin12] Ruby (1.8 and 1.9) allows for stacked quantifiers such as /x{2}{5}/ and appears to treat them more or less as expected, i.e., modulo capturing, /x{2}{5}/ is equivalent to /(x{2}){5}/ is equivalent to /x{10}/. However, in Ruby 1.9, such stacking quantifiers can lead to extreme search time and in ways that are difficult to predict. "x"*1000 =~ /x{2}{5}{8}{3}/ # runs instantly "x"*1000 =~ /x{2}{5}+{8}{3}/ # runs for an unknown but long time "x"*1000 =~ /x{2}{5}+{8}/ # runs instantly "x"*1000 =~ /x{2}{5}+{7}{3}/ # runs instantly "x"*1000 =~ /x{2}{5}+{7}{3} / # runs for an unknown but long time All of the above run instantly in Ruby 1.8. Note that adding parenthesis does not change the runtime. I realize this might not be considered a bug and will take no offense if it as closed as not-a-bug. But it is surprising, and I hope is of interest. -- http://bugs.ruby-lang.org/