Comparative Study of Bourne, Korn, C and Bash Shell

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  • Topic: Unix shell, Bourne shell, Unix
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COURSE: Programming in LINUX environment

COURSE-CODE: CSE-257

TOPIC: Comparative study of Bourne, C, Korn, and Bash Shells.

CONTENTS

Abstract
Introduction
i) Family according to the syntax and grammar
ii) Support (vendor/public domain)
Introduction to Bourne shell
i) Origins
ii) Features of the shell
iii) Criticism
Introduction to C shell
i) Objective
-more like C
-interactive use
ii) Criticism
Introduction to Korn shell
i) History
ii) Uses
Introduction to bash shell
i) Features of bash shell
comparison of command shell
General characteristics
Interactive features
programming features
Conclusion
References

Comparative study of bourne, c, korn, and bash shells.

1. ABSTRACT
This term paper compares the interactive properties of the four shell programs in the UNIX world. The comparison is based on the description of each shell.

2. Introduction
Shell -is software that provide an interface for users of an operating system which provides access to the services of kernel. Many shells are available, either free or commercial. Some of the common shells are Bourne, C, Korn and Bash shell.

Family (according of syntax and grammar)
Bourne-shell flavour
sh, ksh, bash

C-shell flavour
csh, tcsh

Support
Vendor support
sh, ksh, csh

Public domain support
bash

3. INTRODUCTION TO THE BOURNE SHELL (sh)

This Bourne shell[1] is original UNIX shell written by Steve Bourne of Bell laboratory. It is available on all UNIX system. This shell does not have interactive facilities provided by modern shells such as the C shell and korn shell. It is the shell of choice for writing shell programs but it is not a very good choice for interactive use. Bourne shell permits shell scripts to be written and executed. Shell script means we can put commands into a file and then execute that file as we command. The binary program of Bourne shell is located at /bin/sh on most UNIX system. sh is provided by vendor.

Origins:
The original shell is Thompson shell and the Bourne shell was made as replacement for the Thompson shell.

The primary goals were [2]:
To allow shell scripts to be used as filters.

To provide programmability including control flow and variables.

Control over all input/output file descriptors.

Control over signal handling within scripts.

No limits on string lengths when interpreting shell scripts.

Features of Bourne shell [3]:

Scripts can be invoked as commands by using their filename

it may be used interactively or non-interactively

it allow both synchronous and asynchronous execution of commands

it supports input and output redirection and pipelines

sh supports flow control constructs which add power and flexibility to your script.

it provides local and global variable scope

their scripts do not require compilation before execution

it does not have a go to facility, so code restructuring may be necessary

“For ~ do ~ done” loops in particular the use of $* to loop over arguments.

sh provided support for environment variables using keyword parameters and variables.

sh understands several built-in commands, i.e., commands that do not correspond to any program.

Criticism:

Bourne shell was not as friendly for interactive use. But C shell is faster and easier to use.

Even though the UNIX system was written in C, the Bourne shell's grammar looked like ALGOL and not like C.

It lacked an expression grammar.

4. INTRODUCTION TO THE C SHELL (csh)

C shell[6] is UNIX shell created by Bill Joy. This shell provides a C-like language with which to write shell scripts. C shell is a command processor which allow user to type commands which cause actions.

This have interactive features which made it easier and faster to use and its overall style of language look like C and was seen more readable. Csh on most machines...
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