Only a very small subset of them: https://bugs.ruby-lang.org/issues/14240 https://bugs.ruby-lang.org/issues/14240 $/ input record separator (default arg

Only a very small subset of them: https://bugs.ruby-lang.org/issues/14240 https://bugs.ruby-lang.org/issues/14240 $/ input record separator (default argument for "gets") $\ output record separator ("print" prints it at last) $, default separator for Array#join and print $; default separator for String#split As for the gain it's because these variables globally change the behavior of important core methods. They really aren't that useful, but can easily cause havoc.