programming-for-dummies

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Finding an Interpreter
The advantages of interpreted languages
A program run by an interpreter is almost
always slower than the same program compiled
into machine language, so why not compile
every language rather than run them under
an interpreter?
One of the reasons is that creating a compiler for
multiple operating systems is much more difficult
than creating an interpreter for multiple
operating systems. To create a compiler, you
need to know how to translate a programming
language into machine code, but because operating
systems can run under different processors
(such as the PowerPC or Intel processors),
you have to translate language commands into
completely different machine language commands.
Creating a compiler that works correctly
for one processor is hard enough, but creating
that same compiler to work under multiple
processors identically and error-free is much
more difficult.
Compiling a program into machine language is
great when you want to distribute a program to
others. However, languages like Ruby or Perl
are often used to create short programs that run
on a Web server. Using an interpreter may run a
program slower, but you can write a program
and run it right away without compiling it first.
Also, by running the source code directly, interpreters
let you see the source code of each program
that’s running, so you can edit that source
code and run it right away to see how your
changes affect the program. You can still do this
with a compiler, but having to compile a program
and then store a separate executable version of
that program is a minor annoyance that you can
avoid completely just by using an interpreter.
Compilers are great for distributing
programs.
Interpreters are much better for writing and
running shorter programs when you don’t
care whether anyone can see or copy the
source code.
Although JavaScript interpreters can be found in any Web browser, you may
have to download and install interpreters for other programming languages.
Some popular programming languages for running programs on Web servers
(those computers responsible for displaying and retrieving information from
Web pages, such as shopping data) include
✦ PHP (www.php.net)
✦ Perl (www.perl.com)
✦ Python (www.python.org)
✦ Ruby (www.ruby-lang.org)
The preceding four languages not only have free interpreters that you can
copy, but their interpreters also run on different operating systems. That
means a Ruby or Perl program written on a Windows computer should run
identically if copied and run on a Linux or Mac OS X computer.