The number of previous command lines saved. We hope to provide support for those who want to work using a language other than english. See the Graphics section of the Frequently Asked Questions to see how to change this. If you ask to execute one of these then the shell will execute it for you, otherwise it will look for an external program to execute. This is the place where aliases, functions, variables etc are commonly defined.
Aliases are easy to create.
Strings are much the most useful. A variable will not be carried over to subsequent shells unless you export it. Programs written using the shell language are called scripts. Defining these functions gives you a way of customising at a level of complexity higher than that of aliases. Functions can take arguments just as shell scripts can.