UNIX is simple. But It just needs a genius to understand its simplicity.
We will be using Bash, an acronym for "Bourne--Again shell" developed by Brian Fox and Chet Ramey. Bash has become a de facto standard for shell scripting on all flavors of UNIX. Bash is the standard GNU shell, intuitive and flexible. Probably most advisable for beginning users while being at the same time a powerful tool for the advanced and professional user. On Linux, bash is the standard shell for common users. This shell is a so-called superset of the Bourne shell, a set of add-ons and plug-ins. This means that the Bourne Again shell is compatible with the Bourne shell. commands that work in sh, also work in bash. However, the reverse is not always the case. Bash is the POSIX compliant.
Shell is a command language interpreter that executes commands read from the standardInput device(key board) or from a file. Shell is not part of system kernel, but uses the system kernel to execute programs, create files etc. Normally shells are interactive. An interactive shell generally reads from, and writes to, a user's terminal: input and output are connected to a terminal.
The UNIX shell program interprets user commands, which are either directly entered by the user, or which can be read from a file called the shell script or shell program. Shell scripts are interpreted, not compiled.Writing shell script is not hard to learn. The syntax is simple and straightforward, similar to that of invoking and chaining together utilities at the command line, and there are only a few rules to learn. Most short scripts work right the first time, and debugging even the longer ones is straightforward. Shell script is just like batch file in MS-DOS but have more power than the MS-DOS batch file. Shell scripts useful to create our own commands that can save our lots of time and to automate some task of day today life. Using shell scripts we can automate system administrative tasks it saves lot of time