Issue #19784 has been updated by byroot (Jean Boussier). I suspect it's because `"\xFF\xFE1\u00001\u0000" (UTF-8)` has invalid encoding. That said, if `starts_with?` returns true, `delete_prefix` should arguably work. I'll try to see if I can find why, but in the meantime I tested that you can workaround this by casting the string to `Encoding::BINARY`: ```ruby str = "\xff\xfe1\u00001\u0000" str.force_encoding(Encoding::BINARY) str.delete_prefix!("\xff\xfe".b) str.force_encoding(Encoding::UTF_8) p str # => "1\u00001\u0000" ``` ---------------------------------------- Bug #19784: String#delete_prefix! problem https://bugs.ruby-lang.org/issues/19784#change-103973 * Author: inversion (Yura Babak) * Status: Open * Priority: Normal * ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-linux] * Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- Here is the snipped and the question is in the comments: ``` ruby fp = 'with_BOM_16.txt' body = File.read(fp).force_encoding('UTF-8') p body # "\xFF\xFE1\u00001\u0000" p body.start_with?("\xFF\xFE") # true body.delete_prefix!("\xFF\xFE") # !!! why doesn't work? p body # "\xFF\xFE1\u00001\u0000" p body.start_with?("\xFF\xFE") # true body[0, 2] = '' p body # "1\u00001\u0000" p body.start_with?("\xFF\xFE") # false ``` Works same on Linux (ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-linux]) and Windows (ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x64-mingw-ucrt]) -- https://bugs.ruby-lang.org/