Page 130 - DCAP106_OPERATING_SYSTEM_TOOLS

Unit 7: The Shell

important Unix shell written by Stephen Bourne and distributed with Version 7 Unix circa 1978, Notes
and “born again”. BASH was created in 1987 by Brian Fox. In 1990 Chet Ramey became the
primary maintainer.
It is the default shell on most systems which are built on top of the Linux kernel and on Mac OS
X. Also, it can be run on most Unix-like operating systems.Bash has been ported to MS Windows
using Subsystem for UNIX-based Applications (SUA), or POSIX emulation provided by Cygwin
and MSYS.

Did u know? BASH has been ported to MS-DOS by the DJGPP project and to Novell
NetWare.

7.2.2 C Shell (csh)

Bill Joy developed a shell for the BSD Unix system. This shell is known as C shell (csh). Originally,
it was derived from the 6th Edition Unix /bin/sh , the predecessor of the Bourne shell. Its syntax
is modeled after the C programming language. The C shell added many feature improvements
over the Bourne shell, such as aliases and command history. Today, the original C shell is not in
wide use on Unix; it has been superseded by other shells such as the Tenex C shell (tcsh) based
on the original C shell code, but adding filename completion and command line editing, features
later copied in the Korn shell (ksh), and the GNU Bourne-Again shell (BASH). An independently-
developed and modernized C shell, created by Nicole Hamilton, also survives on Windows in
the form of Hamilton C shell.

7.2.3 Korn Shell (ksh)

In the early 80’s, David Korn (AT&T Bell Laboratories) developed a unix shell known as Korn
shell (ksh). It is backwards-compatible with the Bourne shell and includes many features of the
C shell as well, such as a command history, which was inspired by the requests of Bell Labs
users. The main advantage of ksh over the traditional Unix shell is in its use as a programming
language. Since its conception, several features were gradually added, while maintaining strong
backwards compatibility with the Bourne shell.
By means of ksh, we can edit the command line in a WYSIWYG fashion by hitting the suitable
cursor-up or previous-line key-sequence to recall a previous command, and then edit the
command as if the users were in edit line mode. Three modes are available, compatible with vi,
emacs and gmacs.
Since 2000, Korn shell has been an open source software, originally under a license peculiar to
AT&T. However, since the 93q release in early 2005, it has been licensed under the Common
Public License. Korn Shell is available as part of the AT&T Software Technology (AST) Open
Source Software Collection. As ksh was initially only available through a commercial license
from AT&T, a number of free and open source alternatives were created. These include the public
domain pdksh, the Free Software Foundation’s Bourne-Again-Shell bash, and zsh.
Even though many improvements were added by the ksh93 version, some vendors still ship their
own version of the older ksh88 as /bin/ksh, sometimes with extensions ship ksh88, all other
Unix vendors migrated to ksh93 and even Linux distributions started shipping ksh93.

Notes There ksh93 consists of two modified versions which add features for manipulating
the graphical user interface: dtksh which is part of CDE and tksh which provides access to
the Tk widget toolkit.

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