Summary

A shell is a command_interpreter used in a terminal. It runs commands, starts processes, and connects programs. Popular choices: bash, zsh, fish. It reads stdin and writes stdout and stderr. Core features include a prompt, command_history, aliases, globbing, pipes, and redirection. Scripts use shell_script files to automate tasks. Settings come from environment_variables. Many shells follow POSIX_shell rules, but each has unique defaults.