Editing Unix shell (section)

==Concept==
Generally, a ''shell'' is a program that executes other programs in response to text commands. A sophisticated shell can also change the environment in which other programs execute by passing [[environment variable|named variables]], a parameter list, or an input source.

In Unix-like operating systems, users typically have many choices of command-line interpreters for interactive sessions. When a user [[Log in|logs into]] the system interactively, a shell program is automatically executed for the duration of the session. The type of shell, which may be customized for each user, is typically stored in the user's profile, for example in the local {{mono|[[Passwd (file)|passwd]]}} file or in a distributed configuration system such as [[Network Information Service|NIS]] or [[Lightweight Directory Access Protocol|LDAP]]; however, the user may execute any other available shell interactively.

On operating systems with a [[windowing system]], such as [[macOS]] and desktop [[Linux distribution]]s, some users may never use the shell directly. On Unix systems, the shell has historically been the implementation language of system startup scripts, including the program that starts a windowing system, configures networking, and many other essential functions.  However, some system vendors have replaced the traditional shell-based startup system ([[init]]) with different approaches, such as [[systemd]].