From: "nobu (Nobuyoshi Nakada)" Date: 2012-05-04T08:08:30+09:00 Subject: [ruby-core:44863] [ruby-trunk - Feature #6399] IO.read ignores valid open_args on Windows Issue #6399 has been updated by nobu (Nobuyoshi Nakada). Of course, you mean "valid on Windows", I guess. ---------------------------------------- Feature #6399: IO.read ignores valid open_args on Windows https://bugs.ruby-lang.org/issues/6399#change-26436 Author: djberg96 (Daniel Berger) Status: Open Priority: Normal Assignee: Category: Target version: On Microsoft Windows the fopen function accepts many more modes than the standard function: http://msdn.microsoft.com/en-us/library/yeby3zcb(v=vs.80).aspx However, Ruby 1.9 doesn't appear to allow them: # Try to force a sequential scan with 'S', for example IO.read(file, open_args: ['rbS']) # => invalid access mode rbS (ArgumentError) It looks like checks are being made manually in file.c and if they don't match the predetermined flags then an error is raised. I would submit that the flags should be allowed to be passed through, and fopen should fail on its own if they're invalid. -- http://bugs.ruby-lang.org/