Shell Programming

In the early days computers where used to run programs, and nothing more. You punched your program on cards, delivered the pack to the computer department. The staff there loaded the program into the computer, executed it and retrieved the result on paper. This was in turn returned to you and you had to sit down and figure out why you got the result you got.
Modern computers are a little more complex than that. You there have a complete environment where you can execute your programs and even have such astonishing things as interactive programs (hear-hear). It is no longer enough to be able to load your program and just print the result. You also need support to reformat the results, process them in other manners and store them in a database. It would of course be possible to write specially designed programs that formatted the output of your programs according to your wishes, but the number of specialized programs would quickly increase, leaving your computer loaded with programs.
A better approach would be to have a small set of processing programs together with a program made to "glue the parts together." On a UNIX system such a program is called the shell . The shell is used to issue commands, start processes, control jobs, redirect input and output, and other mundane things that you do on a modern computer. Not only that, the shell is a pretty complete programming language.