Chapter 13: Scripting Languages

Why scripting?

Scripting languages are strongest at asking other programs to do something; call it "glue" if you like.

Batch and interactive mode common

REPL-type batch quite common

Brevity is often the case

print "Hello world!"; is likely to work just fine in a scripting language, with perhaps a bit of syntactic sugar.
Reification of quite a bit of user-land experience as syntax for pre-existing objects inside the language environment.

Flexible, dynamic typing is the usual case

Coercion is quite common; also, types can become quite baroque (look at the perlio manual page, for instance)

Primary Access to system-level objects.

io, file/directory manipulation, process management, database access, ipc, networking...

Pattern-matching and string manipulation

PCRE

High-level data types

Sets, bags, dictionaries, lists, tuples, ...

Shells

Truest type of scripting; consists literally of the commands to a given shell
Globs and regular expressions
Pipes and redirection
Here documents
Quoting with interpolation and without
Functions

The crunch-bang

Dire but neat hack

Text processing and report general

PERL = "Practical Extraction and Reporting Language"
Sed, stream editing
Awk, the moribund

Python

Unusually, it actually cares about indentation and end-of-line characters
Structurally, well, some people really like it and some don't; fundamentally, it's not a lot different than most scripting languages, but certainly is willing to take on (and sometimes drop) new features.

Ruby

A purely object-oriented language; the author wanted a language more expressive than Perl and more object-oriented than Python.

Extension languages

If a software package exposes an API, then one can build around that API; while this might be external, the scripting could also incorporated into that environment. For instance, GIMP, Inkscape, and emacs all have significant extension capabilities. Some software packages have their own extension languages; others are more oriented to an API-type environment.

CGI scripting

CGI scripting is quite simple; a process receives a http request (often moderated in some fashion, though not necessarily) and then replies with a similarily formatted response. Text -> text is a modality ideally suited to scripting languages.

CGI scripting

PHP: a lamentable language; of all the languages we will talk about this semester, is probably the most troubled. Widely deployed, it has awkward constructions such as == versus ===.

CGI scripting

Server-side javascript is now competing strongly with PHP; see this article.

Scripting languages and innovation

Names and Scopes
- Wide variety of ideas here: Perl, in its usual accommodating fashion allows about any type of scoping you like; Python and Javascript use classical nesting and lexical scoping
- TCL has unusua methods for "external" scoping (see fig 13.18)

Scripting languages and innovation

TCL, like Pleasant, uses strings for everything

Scripting languages and innovation

Perl has the very unusual idea of letting the program have rather direct access to subroutine parameters as an anonymous array

Scripting languages and innovation

Scripting languages generally have excellent string manipulation tools as built-in features; i.e., there exists language syntax for the tool rather than expressing its use as calls to library routines.

Scripting languages and innovation

One outstanding example is Perl's support for regular expressions as part of the syntax of the language.