Shell commands

I learnt about shell commands. A Shell is an environment which is used to run our commands and programs. It is an user interface with the operating system. There are many different types of shell. I learnt some commands in bash and C shell. Bash is one of the original shell which developed for UNIX computers. C shell was developed based on model of C programming syntax. To know which shell you are using type echo $0.
I learnt how to define variables both in bash and C shell. Bash is denoted by $. The syntax to define a variable is $a = 5
To print the value of the variable use the command echo $a. In C shell we need to set the environment variable. So the syntax goes like this. setenv a 10. An environmental variable has the name and the value.
To go to the home directory ~/.cshrc and ~/.bashrc for C shell and Bash respectively.