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The PWB shell or Mashey shell, sh, was an upward-compatible version of the Thompson shell, augmented by John Mashey and others and distributed with the Programmer's Workbench UNIX, circa 1975–1977. The "rc" suffix on some Unix configuration files (for example, ".vimrc"), is a remnant of the RUNCOM ancestry of Unix shells. Schroeder's Multics shell was itself modeled after the RUNCOM program Louis Pouzin showed to the Multics Team. It was modeled after the Multics shell, developed in 1965 by American software engineer Glenda Schroeder.
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Though not in current use, it is still available as part of some Ancient UNIX systems.
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Though rudimentary by modern standards, it introduced many of the basic features common to all later Unix shells, including piping, simple control structures using if and goto, and filename wildcarding. The first Unix shell was the Thompson shell, sh, written by Ken Thompson at Bell Labs and distributed with Versions 1 through 6 of Unix, from 1971 to 1975. However, some system vendors have replaced the traditional shell-based startup system ( init) with different approaches, such as systemd. 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. On operating systems with a windowing system, such as macOS and desktop Linux distributions, some users may never use the shell directly. The type of shell, which may be customized for each user, is typically stored in the user's profile, for example in the local passwd file or in a distributed configuration system such as NIS or LDAP however, the user may execute any other available shell interactively. When a user logs into the system interactively, a shell program is automatically executed for the duration of the session. In Unix-like operating systems, users typically have many choices of command-line interpreters for interactive sessions. A sophisticated shell can also change the environment in which other programs execute by passing named variables, a parameter list, or an input source. Generally, a shell is a program that executes other programs in response to text commands. All Unix shells provide filename wildcarding, piping, here documents, command substitution, variables and control structures for condition-testing and iteration. Users typically interact with a Unix shell using a terminal emulator however, direct operation via serial hardware connections or Secure Shell are common for server systems. The shell is both an interactive command language and a scripting language, and is used by the operating system to control the execution of the system using shell scripts. Tcsh and sh shell windows on a Mac OS X Leopard desktopĪ Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems.
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