l Builtins 54 5 Shell Variables 55 5.1 Bourne Shell Variables 55 5.2 Bash Variables 55 6 Bash Features 65 6.1 Invoking Bash 65 6.2 Bash Startup Files 67 6.3 Interactive Shells 69 6.3.1 What is an Interactive Shell? 69 6.3.2 Is this Shell Interactive 69 6.3.3 Interactive Shell Beha