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Are All Programs Compiled?

No. As we have seen, there are programs such as shell scripts that do not require compil - ing. They are executed directly. These are written in what are known as scripting or inter- preted languages. These languages have grown in popularity in recent years and include Perl, Python, PHP, Ruby, and many others.

Scripted languages are executed by a special program called an interpreter. An interpreter inputs the program file and reads and executes each instruction contained within it. In

What Is Compiling?

general, interpreted programs execute much more slowly than compiled programs. This is because each source code instruction in an interpreted program is translated every time it is carried out, whereas with a compiled program, a source code instruction is only trans- lated once, and this translation is permanently recorded in the final executable file.

So why are interpreted languages so popular? For many programming chores, the results are “fast enough,” but the real advantage is that it is generally faster and easier to develop interpreted programs than compiled programs. Programs are usually developed in a re- peating cycle of code, compile, test. As a program grows in size, the compilation phase of the cycle can become quite long. Interpreted languages remove the compilation step and thus speed up program development.

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