A Unix Shell variable is an internal variable that a shell maintains. It is local to that Shell. It is not made available to the parent shell or child shell.
We generally use lower case names for shell variables in C shell.
We can set the value of a shell variable by set command.
E.g. % set max_threads=10
To delete a Shell variable we can use unset command.
To use a Shell variable in a script we use $ sign in front of the variable name.
E.g. echo $max_threads