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:
“The new concept of the child as equal and the new integration of children into adult life has helped bring about a gradual but certain erosion of these boundaries that once separated the world of children from the word of adults, boundaries that allowed adults to treat children differently than they treated other adults because they understood that children are different.”
—Marie Winn (20th century)
“It is impossible to dissociate language from science or science from language, because every natural science always involves three things: the sequence of phenomena on which the science is based; the abstract concepts which call these phenomena to mind; and the words in which the concepts are expressed. To call forth a concept, a word is needed; to portray a phenomenon, a concept is needed. All three mirror one and the same reality.”
—Antoine Lavoisier (1743–1794)
“The concept of a person is logically prior to that of an individual consciousness. The concept of a person is not to be analysed as that of an animated body or an embodied anima.”
—Sir Peter Frederick Strawson (b. 1919)