I was just playing with $SAFE in irb and it said "Maybe IRB bug!!" at
the end. Does anyone know what I'm doing wrong? I'm trying to learn
how $SAFE works by experimenting. Should I just do this in "ruby"
instead of "irb" instead?

[shoujoai@lina rb]$ irb
irb(main):001:0> $SAFE
0
irb(main):002:0> $SAFE = 1
1
irb(main):003:0> $SAFE = 2
2
irb(main):004:0> $SAFE = 3
SecurityError: Insecure operation - eval
    from /usr/local/lib/ruby/1.6/irb/workspace.rb:80:in `eval'
    from /usr/local/lib/ruby/1.6/irb/workspace.rb:80:in `evaluate'
    from /usr/local/lib/ruby/1.6/irb/context.rb:126:in `_='
    from /usr/local/lib/ruby/1.6/irb.rb:141:in `eval_input'
    from /usr/local/lib/ruby/1.6/irb.rb:141:in `trace_in'
    from /usr/local/lib/ruby/1.6/irb.rb:141:in `eval_input'
    from /usr/local/lib/ruby/1.6/irb.rb:138:in `signal_status'
    from /usr/local/lib/ruby/1.6/irb.rb:138:in `eval_input'
    from /usr/local/lib/ruby/1.6/irb.rb:136:in `each_top_level_statement'
    from /usr/local/lib/ruby/1.6/irb/ruby-lex.rb:243:in `loop'
    from /usr/local/lib/ruby/1.6/irb/ruby-lex.rb:243:in `each_top_level_statement'
    from /usr/local/lib/ruby/1.6/irb/ruby-lex.rb:216:in `catch'
    from /usr/local/lib/ruby/1.6/irb/ruby-lex.rb:216:in `each_top_level_statement'
    from /usr/local/lib/ruby/1.6/irb.rb:136:in `eval_input'
    from /usr/local/lib/ruby/1.6/irb.rb:68:in `start'
    from /usr/local/lib/ruby/1.6/irb.rb:67:in `catch'
    from /usr/local/lib/ruby/1.6/irb.rb:67:in `start'
    from /usr/local/bin/irb:13Maybe IRB bug!!