shell

• historically the outer hull of the operating system
• users cannot get to the kernel, they can only get to the shell
• command interpreter
• much like ELIZA, it interprets a line of text after it sees a CR on its input stream of bytes
• it breaks down that text according to a grammar
• the commandline consists of multiple commands that can be combined with logical operators or pipes
• each command consists of a program name and a list of arguments
• arguments can be simple strings/paths, switches/flags or key-value-pairs
• Examples: pwd, cd, ls, cat, less, vim
• environment variables (configuration settings and a way of IPC)
• i/o redirection
• pipes