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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 ...
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 ...
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.
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.
The test command in Unix evaluates the expression parameter. In most recent shell implementations, it is a shell builtin, even though the external version still exists.In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces (this is because [is a program and POSIX compatible shells require a space between the program name and its arguments).