What is shell programming

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.
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.