Scripts and Programs

What’s the difference between a script and a program?

Most people to whom I ask this question jump at the idea that a script is interpreted, and indeed, the Wikipedia page on scripting languages currently makes that distinction.  However, there are lots of interpreted programming languages — Basic, Prolog and Smalltalk all leap to mind — so that can’t be it.

So then, most people tend to say something to the effect that scripting isn’t serious, while programming is.  Well, that might be true, but it also has huge implications!  If scripting isn’t serious, then is there any need to apply proper software development practices to scripts?  Do you need to keep scripts under source control?  Do they need requirements?  Do you need to test them thoroughly?  What about documentation?

The assumption that scripts are not serious has serious implications to an organization’s stability.  Organizations that don’t value scripts wind up with a host of arcane code snippets sitting on servers, known only to a handful of sysadmins who have composed them and shared them with others.  When those sysadmins leave, their tools whither in lost directories and the organization breaks.

My own definition is this: a script is a sequence of instructions that is only intended to run once without modification.  Any script that you plan to use more than once is a program and deserves to be treated and cared for with the appropriate respect.

This has the interesting side effect that you can write programs in languages that are called “scripting languages,” and may, like JavaScript, even have “script” in their names.  Perhaps I am swimming upstream, but I would say that the standard definition is useless and indeed dangerous.

So don’t tell me, “there’s just a little script that runs nightly and downloads the billing information,” when what you mean is “there’s a critical csh program…”  Such scripts deserve all our respect!

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