UNIX : Shell and its types
The
shell provides you with an interface to the UNIX system. It gathers
input from you and executes programs based on that input. When a program
finishes executing, it displays that program's output.
A shell is an environment in which we can run our commands, programs, and shell scripts.
The
shell is the utility that processes your requests. When you type in a
command at your terminal, the shell interprets the command and calls the
program that you want. The shell uses standard syntax for all commands.
There
are different flavors of shells, just as there are different flavors of
operating systems. Each flavor of shell has its own set of recognized
commands and functions
In UNIX there are two major types of shells:
- The Bourne shell : If you are using a Bourne-type shell, the default prompt is the $ character.
- The C shell : If you are using a C-type shell, the default prompt is the % character.
There are again various subcategories for Bourne S
hell which are listed as follows :
- Bourne shell ( sh )
- Korn shell ( ksh )
- Bourne Again shell ( bash )
- POSIX shell ( sh )
The different C-type shells follow :
- C shell ( csh )
- TENEX/TOPS C shell ( tcsh )
The original UNIX shell was written in the mid-1970s by Stephen R. Bourne while he was at AT&T Bell Labs in New Jersey.
The Bourne shell was the first shell to appear on UNIX systems, thus it is referred to as "the shell".
The Bourne shell is usually installed as /bin/sh on most versions of UNIX.
For this reason, it is the shell of choice for writing scripts to use on several different versions of UNIX.
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