Clarify rationale for consulting L<feature>.

[perl5.git] / pod / perl.pod

=head1 NAME

perl - The Perl 5 language interpreter

=head1 SYNOPSIS

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

For more information on these options, you can run C<perldoc perlrun>.

=head1 GETTING HELP

The F<perldoc> program gives you access to all the documentation that comes
with Perl.  You can get more documentation, tutorials and community support
online at L<http://www.perl.org/>.

If you're new to Perl, you should start by running C<perldoc perlintro>,
which is a general intro for beginners and provides some background to help
you navigate the rest of Perl's extensive documentation.  Run C<perldoc
perldoc> to learn more things you can do with F<perldoc>.

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

=begin buildtoc

# This section is parsed by Porting/pod_lib.pl for use by pod/buildtoc etc

flag =g  perluniprops perlmodlib perlapi perlintern
flag =go perltoc
flag =ro perlcn perljp perlko perltw
flag =   perlvms

path perlfaq.*               cpan/perlfaq/lib/
path perlglossary            cpan/perlfaq/lib/
path perlxs(?:tut|typemap)?  dist/ExtUtils-ParseXS/lib/
path perldoc                 cpan/Pod-Perldoc/lib/

aux a2p c2ph h2ph h2xs perlbug pl2pm pod2html pod2man s2p splain xsubpp

=end buildtoc

=head2 Overview

    perl		Perl overview (this section)
    perlintro		Perl introduction for beginners
    perlrun		Perl execution and options
    perltoc		Perl documentation table of contents

=head2 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

    perlootut		Perl OO tutorial for beginners

    perlperf		Perl Performance and Optimization Techniques

    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

=head2 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
    perlpodstyle	Perl POD style guide
    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
    perlrebackslash	Perl regular expression backslash sequences
    perlrecharclass	Perl regular expression character classes
    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

    perlport		Perl portability guide
    perllocale		Perl locale support
    perluniintro	Perl Unicode introduction
    perlunicode 	Perl Unicode support
    perlunifaq		Perl Unicode FAQ
    perluniprops	Index of Unicode properties in Perl
    perlunitut		Perl Unicode tutorial
    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
    perlpragma		Perl modules: writing a user pragma

    perlutil		utilities packaged with the Perl distribution

    perlfilter		Perl source filters

    perldtrace		Perl's support for DTrace

    perlglossary	Perl Glossary

=head2 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
    perlxstypemap	Perl XS C/Perl type conversion tools
    perlclib		Internal replacements for standard C library functions
    perlguts		Perl internal functions for those doing extensions
    perlcall		Perl calling conventions from C
    perlmroapi		Perl method resolution plugin interface
    perlreapi		Perl regular expression plugin interface
    perlreguts		Perl regular expression engine internals

    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
    perlsource		Guide to the Perl source tree
    perlinterp		Overview of the Perl interpreter source and how it works
    perlhacktut 	Walk through the creation of a simple C code patch
    perlhacktips	Tips for Perl core C code hacking
    perlpolicy		Perl development policies
    perlgit		Using git with the Perl repository

=head2 Miscellaneous

    perlbook		Perl book information
    perlcommunity	Perl community information

    perldoc		Look up Perl documentation in Pod format

    perlhist		Perl history records
    perldelta		Perl changes since previous version
    perl5174delta	Perl changes in version 5.17.4
    perl5173delta	Perl changes in version 5.17.3
    perl5172delta	Perl changes in version 5.17.2
    perl5171delta	Perl changes in version 5.17.1
    perl5170delta	Perl changes in version 5.17.0
    perl5161delta	Perl changes in version 5.16.1
    perl5160delta	Perl changes in version 5.16.0
    perl5142delta	Perl changes in version 5.14.2
    perl5141delta	Perl changes in version 5.14.1
    perl5140delta	Perl changes in version 5.14.0
    perl5124delta	Perl changes in version 5.12.4
    perl5123delta	Perl changes in version 5.12.3
    perl5122delta	Perl changes in version 5.12.2
    perl5121delta	Perl changes in version 5.12.1
    perl5120delta	Perl changes in version 5.12.0
    perl5101delta	Perl changes in version 5.10.1
    perl5100delta	Perl changes in version 5.10.0
    perl589delta	Perl changes in version 5.8.9
    perl588delta	Perl changes in version 5.8.8
    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
    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

    perlexperiment	A listing of experimental features in Perl

    perlartistic	Perl Artistic License
    perlgpl		GNU General Public License

=head2 Language-Specific

=for buildtoc flag +r

    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)

=head2 Platform-Specific

    perlaix		Perl notes for AIX
    perlamiga		Perl notes for AmigaOS
    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
    perlhaiku		Perl notes for Haiku
    perlhpux		Perl notes for HP-UX
    perlhurd		Perl notes for Hurd
    perlirix		Perl notes for Irix
    perllinux		Perl notes for Linux
    perlmacos		Perl notes for Mac OS (Classic)
    perlmacosx		Perl notes for Mac OS X
    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
    perlriscos		Perl notes for RISC OS
    perlsolaris 	Perl notes for Solaris
    perlsymbian 	Perl notes for Symbian
    perltru64		Perl notes for Tru64
    perlvms		Perl notes for VMS
    perlvos		Perl notes for Stratus VOS
    perlwin32		Perl notes for Windows

=for buildtoc flag -r

=head2 Stubs for Deleted Documents

    perlboot		
    perlbot		
    perltodo
    perltooc		
    perltoot		

=for buildtoc __END__

On a Unix-like system, these documentation files will usually also be
available as manpages for use with the F<man> program.

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

=head1 DESCRIPTION

Perl officially stands for Practical Extraction and Report Language,
except when it doesn't.

Perl was originally a language optimized for scanning arbitrary
text files, extracting information from those text files, and printing
reports based on that information.  It quickly became a good language
for many system management tasks. Over the years, Perl has grown into
a general-purpose programming language. It's widely used for everything
from quick "one-liners" to full-scale application development.

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, B<sed>, B<awk>, and B<sh>, so people familiar with
those languages should have little difficulty with it.  (Language
historians will also note some vestiges of B<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 also has many excellent tools for slicing
and dicing binary data.

But wait, there's more...

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

=over 4

=item *

modularity and reusability using innumerable modules 

Described in L<perlmod>, L<perlmodlib>, and L<perlmodinstall>.

=item *

embeddable and extensible 

Described in L<perlembed>, L<perlxstut>, L<perlxs>, L<perlxstypemap>,
L<perlcall>, L<perlguts>, and L<xsubpp>.

=item *

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

Described in L<perltie> and L<AnyDBM_File>.

=item *

subroutines can now be overridden, autoloaded, and prototyped

Described in L<perlsub>.

=item *

arbitrarily nested data structures and anonymous functions

Described in L<perlreftut>, L<perlref>, L<perldsc>, and L<perllol>.

=item *

object-oriented programming

Described in L<perlobj> and L<perlootut>.

=item *

support for light-weight processes (threads)

Described in L<perlthrtut> and L<threads>.

=item *

support for Unicode, internationalization, and localization

Described in L<perluniintro>, L<perllocale> and L<Locale::Maketext>.

=item *

lexical scoping

Described in L<perlsub>.

=item *

regular expression enhancements

Described in L<perlre>, with additional examples in L<perlop>.

=item *

enhanced debugger and interactive Perl environment,
with integrated editor support

Described in L<perldebtut>, L<perldebug> and L<perldebguts>.

=item *

POSIX 1003.1 compliant library

Described in L<POSIX>.

=back

Okay, that's I<definitely> enough hype.

=head1 AVAILABILITY

Perl is available for most operating systems, including virtually
all Unix-like platforms.  See L<perlport/"Supported Platforms">
for a listing.

=head1 ENVIRONMENT

See L<perlrun>.

=head1 AUTHOR

Larry Wall <larry@wall.org>, 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 perl-thanks@perl.org .

=head1 FILES

 "@INC"			locations of perl libraries

=head1 SEE ALSO

 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

=head1 DIAGNOSTICS

The C<use warnings> pragma (and the B<-w> switch) produces some 
lovely diagnostics.

See L<perldiag> for explanations of all Perl's diagnostics.  The C<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 B<-e> switches, each
B<-e> is counted as one line.)

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

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

=head1 BUGS

The B<-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 C<perl -V>) to perlbug@perl.org .  If you've succeeded
in compiling perl, the L<perlbug> script in the F<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.

=head1 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.