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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.
In Linux, if the script was executed by a regular user, the shell would attempt to execute the command rm -rf / as a regular user, and the command would fail. However, if the script was executed by the root user, then the command would likely succeed and the filesystem would be erased. It is recommended to use sudo on a per-command basis instead.
Support for command history means that a user can recall a previous command into the command-line editor and edit it before issuing the potentially modified command. Shells that support completion may also be able to directly complete the command from the command history given a partial/initial part of the previous command.
COMMAND.COM, the original Microsoft command line processor introduced on MS-DOS as well as Windows 9x, in 32-bit versions of NT-based Windows via NTVDM; cmd.exe, successor of COMMAND.COM introduced on OS/2 and Windows NT systems, although COMMAND.COM is still available in virtual DOS machines on IA-32 versions of those operating systems also.
A script session is captured in file name typescript by default; to specify a different filename follow the script command with a space and the filename as such: script recorded_session. The recorded format of script consists of plain-text timing information (for the whole session) and verbatim command output, including whatever ANSI escape ...
Examples of command-line interpreters include Nushell, DEC's DIGITAL Command Language (DCL) in OpenVMS and RSX-11, the various Unix shells (sh, ksh, csh, tcsh, zsh, Bash, etc.), CP/M's CCP, DOS' COMMAND.COM, as well as the OS/2 and the Windows CMD.EXE programs, the latter groups being based heavily on DEC's RSX-11 and RSTS CLIs.
Application programs may also implement a command-line interface. For example, in Unix-like systems, the telnet program has a number of commands for controlling a link to a remote computer system. Since the commands to the program are made of the same keystrokes as the data being sent to a remote computer, some means of distinguishing the two ...