3. What is a Shell? Different types of Shells, how they differ? list down 3 ways in which BASH differs from TCSH?

A shell in computing refers to a user interface for access to an operating system's services. It is a command-line interpreter that provides a traditional user interface for the Unix operating system and for Unix-like systems. Users direct the operation of the computer by entering commands as text for a command line interpreter to execute or by creating text scripts of one or more such commands.

There are several types of shells in Unix, each with its own set of commands and functions. The most commonly used shells are:

1. Bourne Shell (sh): The original Unix shell, it offers a basic set of features.
2. C Shell (csh): This shell includes a scripting language reminiscent of C language.
3. Korn Shell (ksh): A superset of the Bourne shell, with many features of the C shell and additional ones.
4. Bourne Again Shell (bash): This is a superset of the Bourne shell as well, and includes features from the Korn shell and C shell. It is the default shell for most Unix systems.
5. TENEX C Shell (tcsh): An enhanced version of the C shell, it includes features from the Korn shell and is known for its interactive features.

BASH (Bourne Again SHell) and TCSH (TENEX C Shell) are both Unix shells, but they have some differences:

1. Scripting Syntax: BASH uses a syntax similar to the original Bourne shell. TCSH, on the other hand, uses a syntax similar to the C programming language.
2. Interactive Features: TCSH is known for its interactive features like spelling correction and job control, which are not as prominent in BASH.
3. Compatibility: BASH is a superset of the Bourne shell, which means it includes all features of the Bourne shell plus additional features. TCSH is an enhanced version of the C shell, but it is not fully compatible with it.