Programming is Hard, Let's Go Scripting...

by Larry Wall
December 06, 2007

I think, to most people, scripting is a lot like obscenity. I can't define it, but I'll know it when I see it. Here are some common memes floating around:

    Simple language
    "Everything is a string"
    Rapid prototyping
    Glue language
    Process control
    Compact/concise
    Worse-is-better
    Domain specific
    "Batteries included"

...I don't see any real center here, at least in terms of technology. If I had to pick one metaphor, it'd be easy onramps. And a slow lane. Maybe even with some optional fast lanes.

Easy Onramps

But basically, scripting is not a technical term. When we call something a scripting language, we're primarily making a linguistic and cultural judgment, not a technical judgment.

I see scripting as one of the humanities. It's our linguistic roots showing through. So speaking of roots...

The Past

Suppose you went back to Ada Lovelace and asked her the difference between a script and a program. She'd probably look at you funny, then say something like: Well, a script is what you give the actors, but a program is what you give the audience. That Ada was one sharp lady...

Since her time, we seem to have gotten a bit more confused about what we mean when we say scripting. It confuses even me, and I'm supposed to be one of the experts.

So I'm afraid all I can do is give you my own worm's eye view of the past, the present, and the future. Let me warn you that I am not without a few prejudices here and there.

BASIC

Now, however it was initially intended, I think BASIC turned out to be one of the first major scripting languages, especially the extended version that DEC put onto its minicomputers called BASIC/PLUS, which happily included recursive functions with arguments. I started out as a BASIC programmer. Some people would say that I'm permanently damaged. Some people are undoubtedly right.

But I'm not going to apologize for that. All language designers have their occasional idiosyncracies. I'm just better at it than most. :-)

RSTS BASIC/PLUS

Anyway, when I was a RSTS programmer on a PDP-11, I certainly treated BASIC as a scripting language, at least in terms of rapid prototyping and process control. I'm sure it warped my brain forever. Perl's statement modifiers are straight out of BASIC/PLUS. It even had some cute sigils on the ends of its variables to distinguish string and integer from floating point.

But you could do extreme programming. In fact, I had a college buddy I did pair programming with. We took a compiler writing class together and studied all that fancy stuff from the dragon book. Then of course the professor announced we would be implementing our own language, called PL/0. After thinking about it a while, we announced that we were going to do our project in BASIC. The professor looked at us like were insane. Nobody else in the class was using BASIC. And you know what? Nobody else in the class finished their compiler either. We not only finished but added I/O extensions, and called it PL 0.5. That's rapid prototyping.

Unix?

I remember one day our computer center got a letter from Bell Labs telling us that we could get a tape of Unix V6 for cheap, only $100 because they were coming out shortly with V7. We all looked at each other and said, Why would we ever want to use this thing called Unix? We have RSTS.

JAM (no not that one)

My first scripting language was written in BASIC. For my job in the computer center I wrote a language that I called JAM, short for Jury-rigged All-purpose Meta-language. Story of my life...

JAM was an inside-out text-processing language much like PHP, except that HTML hadn't been invented yet. We mostly used it as a fancy macro processor for BASIC. Unlike PHP, it did not have 3,000 functions in one namespace. We wouldn't have had the memory, for one thing.

LISP

For good or ill, when I went off to grad school, I studied linguistics, so the only computer language I used there was LISP. It was my own personal McCarthy era.

Is LISP a candidate for a scripting language? While you can certainly write things rapidly in it, I cannot in good conscience call LISP a scripting language. By policy, LISP has never really catered to mere mortals.

And, of course, mere mortals have never really forgiven LISP for not catering to them.

Pascal, Ada

Once I got into industry, I wrote a compiler in Pascal for a discrete event simulator, and slavered over the forthcoming Ada specs. As a linguist, I don't think of Ada as a big language. Now, English and Japanese, those are big languages. Ada is just a medium-sized language.

Unix, shell

After several years I finally became acquainted with Unix and its various scripting languages. OK, to be more precise, BSD, and csh.

BSD, csh

Yeah, yeah, I know. More brain damage...

I also learned a little C.

C

That's because a little C is all there is. I'm still learning those libraries though.

shell + awk + sed + find + expr...

But the frustrations of Unix shell programming led directly to the creation of Perl, which I don't really have time to tell. But essentially, I found that shell scripting was intrinsically limited by the fact that most of its verbs are not under its control and hence largely inconsistent with each other. And the nouns are impoverished, restricted to strings and files, with who-knows-what typology.

C xor shell

More destructive was the mindset that it was a one-dimensional universe: you either programmed in C or you programmed in shell, because they're obviously at opposite ends of the One True Continuum. Perl came about when I realized that scripting did not always have to viewed as the opposite of programming, but that a single language could be pretty good for both. That opened up a huge ecological niche. Many of you have seen my old clamshell diagram, with the two dimensions of manipulexity and whipuptitude.

Tcl

After Perl came Tcl, which in a sense is a purer scripting language than Perl. Perl just pretends that everything is a string when it's convenient, but Tcl really believes that as a controlling metaphor. The string metaphor tends to have bad performance ramifications, but that's not why Tcl languished, I think. There were two reasons for that.

First, Tcl stayed in the Unix mindset that controlling tools was the opposite of creating tools, so they didn't optimize much. The fast parts can always be written in C, after all.

The second reason was the lack of a decent extension mechanism, so you ended up with separate executables for expect, incr-tcl, etc.

I must say, though, that I've always admired Tcl's delegational model of semantics. But it fell into the same trap as LISP by expecting everyone to use the One True Syntax. Speaking of the One True Syntax:

Python

After Tcl came Python, which in Guido's mind was inspired positively by ABC, but in the Python community's mind was inspired negatively by Perl. I'm not terribly qualified to talk about Python however. I don't really know much about Python. I only stole its object system for Perl 5. I have since repented.

Ruby

I'm much more qualified to talk about Ruby--that's because a great deal of Ruby's syntax is borrowed from Perl, layered over Smalltalk semantics. I've always viewed Ruby as a much closer competitor for Perls ecological niche, not just because of the borrowed ideas, but because both Perl and Ruby take their functional programming support rather more seriously that Python does. On the other hand, I think Ruby kind of screwed up on its declaration syntax, among other things.

*sh

Meanwhile, the Bourne shell was extended into the Korn shell and bash. I didn't have much to do with those either. Thankfully. I will say that the continued evolution of the shell shows just how crufty a language can get when you just keep adding on ad hoc syntactic features.

Pages: 1, 2, 3

Next Page