Perl
<language, tool> A high-level programming language, started by
Larry Wall in 1987 and developed as an
open source project.
It has an eclectic heritage, deriving from the ubiquitous
C programming language and to a lesser extent from
sed,
awk, various
Unix shell languages,
Lisp, and at least a dozen other tools and languages.
Originally developed for
Unix, it is now available for many platforms.
Perl's elaborate support for
regular expression matching and substitution has made it the language of choice for tasks involving string manipulation, whether for text or binary data.
It is particularly popular for writing CGI scripts.
The language's highly flexible syntax and concise regular expression operators, make densely written Perl code indecipherable to the uninitiated.
The syntax is, however, really quite simple and powerful and, once the basics have been mastered, a joy to write.
Perl's only
primitive data type is the "scalar", which can hold a number, a string, the undefined value, or a typed reference.
Perl's aggregate data types are arrays, which are ordered lists of scalars indexed by natural numbers, and hashes (or "associative arrays") which are unordered lists of scalars indexed by strings.
A reference can point to a scalar, array, hash,
function, or filehandle.
Objects are implemented as references "blessed" with a
class name. Strings in Perl are
eight-bit clean, including nulls, and so can contain
binary data.
Unlike C but like most Lisp dialects, Perl internally and dynamically handles all memory allocation,
garbage collection, and type
coercion.
Perl supports closures, recursive functions, symbols with either
lexical scope or
dynamic scope, nested data structures of arbitrary content and complexity (as lists or hashes of references), and packages (which can serve as classes, optionally inheriting
methods from one or more other classes).
There is ongoing work on threads,
Unicode, exceptions, and
backtracking.
Perl program files can contain embedded documentation in
POD (Plain Old Documentation), a simple markup language.
The normal Perl distribution contains documentation for the language, as well as over a hundred modules (program libraries).
Hundreds more are available from The
Comprehensive Perl Archive Network.
Modules are themselves generally written in Perl, but can be implemented as interfaces to code in other languages, typically compiled C.
The free availability of modules for almost any conceivable task, as well as the fact that Perl offers direct access to almost all system calls and places no arbitrary limits on data structure size or complexity, has led some to describe Perl, in a parody of a famous remark about
lex, as the "Swiss Army chainsaw" of programming.
The use of Perl has grown significantly since its adoption as the language of choice of many
World-Wide Web developers.
CGI interfaces and libraries for Perl exist for several platforms and Perl's speed and flexibility make it well suited for form processing and on-the-fly
web page creation.
Perl programs are generally stored as
text source files, which are compiled into
virtual machine code at run time; this, in combination with its rich variety of data types and its common use as a glue language, makes Perl somewhat hard to classify as either a "
scripting language" or an "
applications language" -- see
Ousterhout's dichotomy. Perl programs are usually called "Perl scripts", if only for historical reasons.
Version 5 was a major rewrite and enhancement of version 4, released sometime before November 1993.
It added real data structures by way of "references", un-adorned
subroutine calls, and
method inheritance.
The spelling "Perl" is preferred over the older "PERL" (even though some explain the language's name as originating in the acronym for "Practical Extraction and Report Language").
The program that interprets/compiles Perl code is called "perl", typically "/usr/local/bin/perl" or "/usr/bin/perl".
Current version: 5.005_03 stable, 5.005_62 in development, as of 1999-12-04.
Home (http://www.perl.com/).
Usenet newsgroups: news:comp.lang.perl.announce, news:comp.lang.perl.misc.
["Programming Perl", Larry Wall and Randal L. Schwartz, O'Reilly & Associates, Inc.
Sebastopol, CA.
ISBN 0-93715-64-1].
["Learning Perl" by Randal L. Schwartz, O'Reilly & Associates, Inc., Sebastopol, CA].
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Jargon File]
