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Unix shell

From Academic Kids

A Unix shell, also called "the command line", provides the traditional user interface for the Unix operating system. Users direct the operation of the computer by entering command input as text for a shell to execute. Within the Microsoft Windows suite of operating systems the analogous program is command.com, or cmd.exe for Windows NT-based operating systems.

The most generic sense of the term shell means any program that users use to type commands; it is called a "shell" because it hides the details of the underlying operating system behind the shell's interface (contrast "kernel", which refers to the lowest-level, or 'inner-most' component of an operating system). Similarly, graphical user interfaces for Unix, such as GNOME and KDE, are sometimes called visual shells or graphical shells. By itself, the term shell is usually associated with the command line. In Unix, any program can be the user's shell; users who want to use a different syntax for typing commands can specify a different program as their shell.

The term shell also refers to a particular program, namely the Bourne shell, sh. The Bourne shell was the shell used in early versions of Unix and became a de facto standard; every Unix-like system has the equivalent of the Bourne shell. The Bourne shell program is located in the UNIX file hierarchy at /bin/sh. On some systems, such as BSD, /bin/sh is a Bourne shell or equivalent, but on other systems such as Linux, /bin/sh is likely to be a link to a compatible, but more feature-rich shell, such as Bash. POSIX specifies the standard shell as a strict subset of the Korn shell.

The Unix shell is unusual since it is in both an interactive command language and the language used to script the system; it is a scripting programming language.

On systems using a windowing system, some users may never use the shell directly, though on Unix systems, the shell is still the implementation language of system startup scripts, including the program that starts the windowing system, the program that dials into the Internet, and many other essential functions.

On Windows, equivalents to Unix system scripts are called batch files, and have a ".bat" extension.

Many regular users of a UNIX system still find a modern command line shell much more convenient for many tasks than any GUI application.

Contents

Unix shells

Historic

See also

External links

fr:Shell ja:シェル no:Unix-skall pl:Sh ru:Unix shell zh:Unix shell

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