实用报表提取语言 Perl : Practical Extraction and Report Language

Perl 最初的设计者为拉里·沃尔（Larry Wall），他于1987年12月18日发表。Perl借取了C、sed、awk、shell scripting以及很多其他程序语言的特性。其中最重要的特性是它内部集成了正则表达式的功能，以及巨大的第三方代码库CPAN。简而言之，Perl象C一样强大，象awk、sed等脚本描述语言一样方便。Perl 一般被称为“实用报表提取语言”（Practical Extraction and Report Language），你也可能看到“perl”，所有的字母都是小写的。一般，“Perl”，有大写的 P，是指语言本身，而“perl”，小写的 p，是指程序运行的解释器。

perl的前身是Unix系统管理的一个工具，被用在无数的小任务里。后逐渐发展成为一种功能强大的程序设计语言，用作Web编程、数据库处理、XML处理以及系统管理；在完成这些工作时，同时仍能处理日常细小工作，这是它的设计初衷。Perl特别适合系统管理和Web编程。实际上已经被用在所有Unix(包括Linux)捆绑在一起作为标准部件发布，同时也用在Microsoft Windows和几乎其他所有操作系统。Perl的应用很广泛，依靠Perl工作更容易、更有效。

NAME
perl - Practical Extraction and Report Language

SYNOPSIS
perl [ -sTtuUWX ] [ -hv ] [ -V[:*configvar*] ]
[ -cw ] [ -d[t][:*debugger*] ] [ -D[*number/list*] ]
[ -pna ] [ -F*pattern* ] [ -l[*octal*] ] [ -0[*octal/hexadecimal*] ]
[ -I*dir* ] [ -m[-]*module* ] [ -M[-]*'module...'* ] [ -f ]
[ -C [*number/list*] ] [ -P ] [ -S ] [ -x[*dir*] ] [ -i[*extension*] ]
[ -e *'command'* ] [ -- ] [ *programfile* ] [ *argument* ]...

If you're new to Perl, you should start with perlintro, which is a
general intro for beginners and provides some background to help you
navigate the rest of Perl's extensive documentation.

For ease of access, the Perl manual has been split up into several
sections.

Overview
perl Perl overview (this section)
perlintro Perl introduction for beginners
perltoc Perl documentation table of contents

ActivePerl ActivePerl overview

Tutorials
perlreftut Perl references short introduction
perldsc Perl data structures intro
perllol Perl data structures: arrays of arrays

perlrequick Perl regular expressions quick start
perlretut Perl regular expressions tutorial

perlboot Perl OO tutorial for beginners
perltoot Perl OO tutorial, part 1
perltooc Perl OO tutorial, part 2
perlbot Perl OO tricks and examples

perlstyle Perl style guide

perlcheat Perl cheat sheet
perltrap Perl traps for the unwary
perldebtut Perl debugging tutorial

perlfaq Perl frequently asked questions
perlfaq1 General Questions About Perl
perlfaq2 Obtaining and Learning about Perl
perlfaq3 Programming Tools
perlfaq4 Data Manipulation
perlfaq5 Files and Formats
perlfaq6 Regexes
perlfaq7 Perl Language Issues
perlfaq8 System Interaction
perlfaq9 Networking

Reference Manual
perlsyn Perl syntax
perldata Perl data structures
perlop Perl operators and precedence
perlsub Perl subroutines
perlfunc Perl built-in functions
perlopentut Perl open() tutorial
perlpacktut Perl pack() and unpack() tutorial
perlpod Perl plain old documentation
perlpodspec Perl plain old documentation format specification
perlrun Perl execution and options
perldiag Perl diagnostic messages
perllexwarn Perl warnings and their control
perldebug Perl debugging
perlvar Perl predefined variables
perlre Perl regular expressions, the rest of the story
perlreref Perl regular expressions quick reference
perlref Perl references, the rest of the story
perlform Perl formats
perlobj Perl objects
perltie Perl objects hidden behind simple variables
perldbmfilter Perl DBM filters

perlipc Perl interprocess communication
perlfork Perl fork() information
perlnumber Perl number semantics

perlthrtut Perl threads tutorial
perlothrtut Old Perl threads tutorial

perlport Perl portability guide
perllocale Perl locale support
perluniintro Perl Unicode introduction
perlunicode Perl Unicode support
perlebcdic Considerations for running Perl on EBCDIC platforms

perlsec Perl security

perlmod Perl modules: how they work
perlmodlib Perl modules: how to write and use
perlmodstyle Perl modules: how to write modules with style
perlmodinstall Perl modules: how to install from CPAN
perlnewmod Perl modules: preparing a new module for distribution

perlutil utilities packaged with the Perl distribution

perlcompile Perl compiler suite intro

perlfilter Perl source filters

perlglossary Perl Glossary

Internals and C Language Interface
perlembed Perl ways to embed perl in your C or C++ application
perldebguts Perl debugging guts and tips
perlxstut Perl XS tutorial
perlxs Perl XS application programming interface
perlclib Internal replacements for standard C library functions
perlguts Perl internal functions for those doing extensions
perlcall Perl calling conventions from C

perlapi Perl API listing (autogenerated)
perlintern Perl internal functions (autogenerated)
perliol C API for Perl's implementation of IO in Layers
perlapio Perl internal IO abstraction interface

perlhack Perl hackers guide

Miscellaneous
perlbook Perl book information
perltodo Perl things to do

perldoc Look up Perl documentation in Pod format

perlhist Perl history records
perldelta Perl changes since previous version
perl587delta Perl changes in version 5.8.7
perl586delta Perl changes in version 5.8.6
perl585delta Perl changes in version 5.8.5
perl584delta Perl changes in version 5.8.4
perl583delta Perl changes in version 5.8.3
perl582delta Perl changes in version 5.8.2
perl581delta Perl changes in version 5.8.1
perl58delta Perl changes in version 5.8.0
perl573delta Perl changes in version 5.7.3
perl572delta Perl changes in version 5.7.2
perl571delta Perl changes in version 5.7.1
perl570delta Perl changes in version 5.7.0
perl561delta Perl changes in version 5.6.1
perl56delta Perl changes in version 5.6
perl5005delta Perl changes in version 5.005
perl5004delta Perl changes in version 5.004

activeperl-release Release notes for ActivePerl
activeperl-changes ActivePerl revision history

perlartistic Perl Artistic License
perlgpl GNU General Public License

Language-Specific
perlcn Perl for Simplified Chinese (in EUC-CN)
perljp Perl for Japanese (in EUC-JP)
perlko Perl for Korean (in EUC-KR)
perltw Perl for Traditional Chinese (in Big5)

Platform-Specific
perlaix Perl notes for AIX
perlamiga Perl notes for AmigaOS
perlapollo Perl notes for Apollo DomainOS
perlbeos Perl notes for BeOS
perlbs2000 Perl notes for POSIX-BC BS2000
perlce Perl notes for WinCE
perlcygwin Perl notes for Cygwin
perldgux Perl notes for DG/UX
perldos Perl notes for DOS
perlepoc Perl notes for EPOC
perlfreebsd Perl notes for FreeBSD
perlhpux Perl notes for HP-UX
perlhurd Perl notes for Hurd
perlirix Perl notes for Irix
perllinux Perl notes for Linux
perlmachten Perl notes for Power MachTen
perlmacos Perl notes for Mac OS (Classic)
perlmacosx Perl notes for Mac OS X
perlmint Perl notes for MiNT
perlmpeix Perl notes for MPE/iX
perlnetware Perl notes for NetWare
perlopenbsd Perl notes for OpenBSD
perlos2 Perl notes for OS/2
perlos390 Perl notes for OS/390
perlos400 Perl notes for OS/400
perlplan9 Perl notes for Plan 9
perlqnx Perl notes for QNX
perlsolaris Perl notes for Solaris
perltru64 Perl notes for Tru64
perluts Perl notes for UTS
perlvmesa Perl notes for VM/ESA
perlvms Perl notes for VMS
perlvos Perl notes for Stratus VOS
perlwin32 Perl notes for Windows

By default, the manpages listed above are installed in the
/usr/local/man/ directory.

Extensive additional documentation for Perl modules is available. The
default configuration for perl will place this additional documentation
in the /usr/local/lib/perl5/man directory (or else in the man
subdirectory of the Perl library directory). Some of this additional
documentation is distributed standard with Perl, but you'll also find
documentation for third-party modules there.

You should be able to view Perl's documentation with your man(1) program
by including the proper directories in the appropriate start-up files,
or in the MANPATH environment variable. To find out where the
configuration has installed the manpages, type:

perl -V:man.dir

If the directories have a common stem, such as /usr/local/man/man1 and
/usr/local/man/man3, you need only to add that stem (/usr/local/man) to
your man(1) configuration files or your MANPATH environment variable. If
they do not share a stem, you'll have to add both stems.

If that doesn't work for some reason, you can still use the supplied
perldoc script to view module information. You might also look into
getting a replacement man program.

If something strange has gone wrong with your program and you're not
sure where you should look for help, try the -w switch first. It will
often point out exactly where the trouble is.

DESCRIPTION
Perl is a language optimized for scanning arbitrary text files,
extracting information from those text files, and printing reports based
on that information. It's also a good language for many system
management tasks. The language is intended to be practical (easy to use,
efficient, complete) rather than beautiful (tiny, elegant, minimal).

Perl combines (in the author's opinion, anyway) some of the best
features of C, sed, awk, and sh, so people familiar with those languages
should have little difficulty with it. (Language historians will also
note some vestiges of csh, Pascal, and even BASIC-PLUS.) Expression
syntax corresponds closely to C expression syntax. Unlike most Unix
utilities, Perl does not arbitrarily limit the size of your data--if
you've got the memory, Perl can slurp in your whole file as a single
string. Recursion is of unlimited depth. And the tables used by hashes
(sometimes called "associative arrays") grow as necessary to prevent
degraded performance. Perl can use sophisticated pattern matching
techniques to scan large amounts of data quickly. Although optimized for
scanning text, Perl can also deal with binary data, and can make dbm
files look like hashes. Setuid Perl scripts are safer than C programs
through a dataflow tracing mechanism that prevents many stupid security
holes.

If you have a problem that would ordinarily use sed or awk or sh, but it
exceeds their capabilities or must run a little faster, and you don't
want to write the silly thing in C, then Perl may be for you. There are
also translators to turn your sed and awk scripts into Perl scripts.

But wait, there's more...

Begun in 1993 (see perlhist), Perl version 5 is nearly a complete
rewrite that provides the following additional benefits:

* modularity and reusability using innumerable modules

Described in perlmod, perlmodlib, and perlmodinstall.

* embeddable and extensible

Described in perlembed, perlxstut, perlxs, perlcall, perlguts, and
xsubpp.

* roll-your-own magic variables (including multiple simultaneous DBM
implementations)

Described in perltie and AnyDBM_File.

* subroutines can now be overridden, autoloaded, and prototyped

Described in perlsub.

* arbitrarily nested data structures and anonymous functions

Described in perlreftut, perlref, perldsc, and perllol.

* object-oriented programming

Described in perlobj, perlboot, perltoot, perltooc, and perlbot.

* support for light-weight processes (threads)

Described in perlthrtut and threads.

* support for Unicode, internationalization, and localization

Described in perluniintro, perllocale and Locale::Maketext.

* lexical scoping

Described in perlsub.

* regular expression enhancements

Described in perlre, with additional examples in perlop.

* enhanced debugger and interactive Perl environment, with integrated
editor support

Described in perldebtut, perldebug and perldebguts.

* POSIX 1003.1 compliant library

Described in POSIX.

Okay, that's *definitely* enough hype.

AVAILABILITY
Perl is available for most operating systems, including virtually all
Unix-like platforms. See "Supported Platforms" in perlport for a
listing.

ENVIRONMENT
See perlrun.

AUTHOR
Larry Wall <[e-mail]>, with the help of oodles of other folks.

If your Perl success stories and testimonials may be of help to others
who wish to advocate the use of Perl in their applications, or if you
wish to simply express your gratitude to Larry and the Perl developers,
please write to [e-mail] .

FILES
"@INC" locations of perl libraries

SEE ALSO
a2p awk to perl translator
s2p sed to perl translator

http://www.perl.org/ the Perl homepage
http://www.perl.com/ Perl articles (O'Reilly)
http://www.cpan.org/ the Comprehensive Perl Archive
http://www.pm.org/ the Perl Mongers

DIAGNOSTICS
The "use warnings" pragma (and the -w switch) produces some lovely
diagnostics.

See perldiag for explanations of all Perl's diagnostics. The "use
diagnostics" pragma automatically turns Perl's normally terse warnings
and errors into these longer forms.

Compilation errors will tell you the line number of the error, with an
indication of the next token or token type that was to be examined. (In
a script passed to Perl via -e switches, each -e is counted as one
line.)

Setuid scripts have additional constraints that can produce error
messages such as "Insecure dependency". See perlsec.

Did we mention that you should definitely consider using the -w switch?

BUGS
The -w switch is not mandatory.

Perl is at the mercy of your machine's definitions of various operations
such as type casting, atof(), and floating-point output with sprintf().

If your stdio requires a seek or eof between reads and writes on a
particular stream, so does Perl. (This doesn't apply to sysread() and
syswrite().)

While none of the built-in data types have any arbitrary size limits
(apart from memory size), there are still a few arbitrary limits: a
given variable name may not be longer than 251 characters. Line numbers
displayed by diagnostics are internally stored as short integers, so
they are limited to a maximum of 65535 (higher numbers usually being
affected by wraparound).

You may mail your bug reports (be sure to include full configuration
information as output by the myconfig program in the perl source tree,
or by "perl -V") to [e-mail] . If you've succeeded in compiling
perl, the perlbug script in the utils/ subdirectory can be used to help
mail in a bug report.

Perl actually stands for Pathologically Eclectic Rubbish Lister, but
don't tell anyone I said that.

NOTES
The Perl motto is "There's more than one way to do it." Divining how
many more is left as an exercise to the reader.

The three principal virtues of a programmer are Laziness, Impatience,
and Hubris. See the Camel Book for why.