Linux SHELL Overview

Linux SHELL Overview :- Shell is the integral part of UNIX/LINUX system. It is responsible for accepting commands from the user, interpreting them and then passing them on to kernel for processing. Shell acts as a user interface.

The Three Major Shells For UNIX/LINUX System.

a). Bourne shell

b). C shell

c). Korn shell

d). Bash shell

a). Bourne Shell

Bourne shell is the oldest among all Unix shells. It was create by Dr. Steven Bourne at AT&T Bell Laboratory.

It Provides The Following Features:-

# Use of wildcards. Like ?,*.

# Input and output redirection.

# A set of shell variables for customizing the shell environment.

# Background execution of commands.

# Command set, loop constructs and conditional statements for writing shell scripts.

b). C Shell

C shell was developed by bill joy at university of California, Berkeley. It was developed as an alternative to the Bourne shell. It is the standard shell on UNIX system derived from BSD (Berkeley Software Distributions).

It Provides The Following Features:-

# Use of wildcards.

# Input and output redirection.

# A set of shell variables of customizing the shell environment.

# Integer arithmetic.

# History mechanism that remembers previously executed commands.

# Aliasing for abbreviating frequently used commands.

# A built in set of operators based on the C programming language for writing shell scripts.

c). Korn Shell

Korn shell was developed by David Korn at AT&T Lab. It is the standard shell on UNIX systems based on system V. It is an upward compatible extension of Bourne shell. All that works on Bourne shell also works on Korn shell.

It Provides The Following Features:-

# History mechanism that remembers previously executed commands.

# Aliasing for abbreviating frequently used commands.

# Pattern matching for file names.

# Interactive editing of the command line with either emacs or vi editor.

# Better function definitions providing local variables and the ability to create recursive functions.

# Home directory can be represented by a tilde (~) sign.  

d). Bash Shell

Bash shell was released by brian for fox andchet Ramey as part of the free software foundation GNU project. Extensively used in Linux systems, it provides all the features found in Bourne C and Korn shell.

It Provides The Following Features:-

# Input and output redirection.

# Command line editing.

# Tilde representation.

# Built in shell commands and variables command history, aliasing etc.

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