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.

INTODUCTION TO GCC ON LINUX

GCC stands for "GNU Compiler Collection". GCC is an integrated distribution of compilers for several major programming languages. These languages currently include C, C++, Objective-C, Java, Fortran, and Ada.

The abbreviation GCC has multiple meanings in common use. The current official meaning is "GNU Compiler Collection", which refers generically to the complete suite of tools. The name historically stood for "GNU C Compiler", and this usage is still common when the emphasis is on compiling C programs. Finally, the name is also used when speaking of the language-independent component of GCC: code shared among the compilers for all supported languages.

The language-independent component of GCC includes the majority of the optimizers, as well as the "back ends" that generate machine code for various processors.

The part of a compiler that is specific to a particular language is called the "front end". In addition to the front ends that are integrated components of GCC, there are several other front ends that are maintained separately. These support languages such as Pascal, Mercury, and COBOL. To use these, they must be built together with GCC proper.

Most of the compilers for languages other than C have their own names. The C++ compiler is G++, the Ada compiler is GNAT, and so on. When we talk about compiling one of those languages, we might refer to that compiler by its own name, or as GCC. Either is correct.

Historically, compilers for many languages, including C++ and Fortran, have been implemented as "preprocessors" which emit another high level language such as C. None of the compilers included in GCC are implemented this way; they all generate machine code directly. This sort of preprocessor should not be confused with the C preprocessor, which is an integral feature of the C, C++, and Objective-C languages.