Concept
The most generic sense of the term shell means any program that users employ to type commands. A shell hides the details of the underlying operating system with the shell interface and manages the technical details of the operating system kernel interface, which is the lowest-level, or 'inner-most' component of most operating systems. In Unix-like operating systems users typically have many choices of command-line interpreters for interactive sessions. When a user logs in to the system, a shell program is automatically executed. The login shell may be customized for each user, typically in the passwd file, and can be customized via passwd -e, or on some systems via the chsh program. In addition, a user is typically allowed to execute another shell program interactively.
The Unix shell was unusual when it was introduced. It is both an interactive command language as well as a scripting programming language, and is used by the operating system as the facility to control (shell script) the execution of the system. Shells created for other operating systems than Unix, often provide similar functionality.
On systems with a windowing system, some users may never use the shell directly. On Unix systems, the shell is still the implementation language of system startup scripts, including the program that starts the windowing system, the programs that facilitate access to the Internet, and many other essential functions.
Graphical user interfaces for Unix, such as GNOME, KDE, and Xfce are often called visual or graphical shells.
Read more about this topic: Unix Shell
Famous quotes containing the word concept:
“Teaching Black Studies, I find that students are quick to label a black person who has grown up in a predominantly white setting and attended similar schools as “not black enough.” ...Our concept of black experience has been too narrow and constricting.”
—bell hooks (b. c. 1955)
“Obscenity is a moral concept in the verbal arsenal of the Establishment, which abuses the term by applying it, not to expressions of its own morality, but to those of another.”
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“By speaking, by thinking, we undertake to clarify things, and that forces us to exacerbate them, dislocate them, schematize them. Every concept is in itself an exaggeration.”
—José Ortega Y Gasset (1883–1955)