Issue #8023 has been updated by pietzcker (Tim Pietzcker). Tested on Ruby 2.0.0 and 1.9.3p392 ---------------------------------------- Bug #8023: Lookbehind assertion fails with /m mode enabled https://bugs.ruby-lang.org/issues/8023#change-37316 Author: pietzcker (Tim Pietzcker) Status: Open Priority: Normal Assignee: Category: Target version: ruby -v: ruby 2.0.0p0 (2013-02-24) [x64-mingw32] Lookbehind assertions fail if they are longer than one character, and if dotall mode is set. irb(main):001:0> "foo" =~ /(?<=f).*/m => 1 irb(main):002:0> "foo" =~ /(?<=fo).*/m => nil The latter should have matched the "o". This only seems to happen with dotall mode turned on (dot matches newline); without it, everything is OK: irb(main):003:0> "foo" =~ /(?<=f).*/ => 1 irb(main):004:0> "foo" =~ /(?<=fo).*/ => 2 -- http://bugs.ruby-lang.org/