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A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating 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 .
A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. [1] The various dialects of shell scripts are considered to be command languages . Typical operations performed by shell scripts include file manipulation, program execution, and printing text.
Version 1 AT&T UNIX printf: Shell programming Mandatory Write formatted output 4.3BSD-Reno prs: SCCS Optional (XSI) Print an SCCS file PWB UNIX ps: Process management Mandatory Report process status Version 4 AT&T UNIX pwd: Filesystem Mandatory Print working directory Version 5 AT&T UNIX read: Shell programming Mandatory Read a line from ...
Commands external to the shell: Separate UNIX-style programs such as ls or ln, and; Shell scripts, which are files containing executable commands. (Shell scripts do not require compilation before execution and, when certain requirements are met, can be invoked as commands by using their filename.) The resulting string is executed as a command.
A shell script (or job) can report progress of long running tasks to the interactive user. Unix/Linux systems may offer other tools support using progress indicators from scripts or as standalone-commands, such as the program "pv". [52] These are not integrated features of the shells, however.
There are many variants of Unix shell: Bourne shell sh. Almquist shell (ash) Debian Almquist shell (dash) Bash (Unix shell) bash; KornShell ksh. Z shell zsh; C shell csh. TENEX C shell tcsh; Ch shell ch; Emacs shell eshell; Friendly interactive shell fish; PowerShell pwsh; rc shell rc, a shell for Plan 9 from Bell Labs and Unix; Stand-alone ...
Conversely, some programming languages can be used interactively from an operating system shell or in a purpose-built program. Several command-line shells, such as Nushell, Xonsh, Bash (Unix shell), and Z shell, offer command-line completion, enabling the interpreter to expand commands based on a few characters input by the user. [12]
The Z shell (Zsh) is a Unix shell that can be used as an interactive login shell and as a command interpreter for shell scripting. Zsh is an extended Bourne shell with many improvements, including some features of Bash, ksh, and tcsh. Zsh was created by Paul Falstad in 1990 while he was a student at Princeton University.