change#2879 broke rvalue autovivification of magicals such as ${$num}

[p5sagit/p5-mst-13.2.git] / pod / perl.pod

=head1 NAME

perl - Practical Extraction and Report Language

=head1 SYNOPSIS

B<perl>	S<[ B<-sTuU> ]> S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
    S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]>
    S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]>
    S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]>
    S<[ B<-P> ]> S<[ B<-S> ]> S<[ B<-x>[I<dir>] ]>
    S<[ B<-i>[I<extension>] ]> S<[ B<-e> I<'command'> ] 
    [ B<--> ] [ I<programfile> ] [ I<argument> ]...>

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

    perl		Perl overview (this section)
    perldelta		Perl changes since previous version
    perl5005delta	Perl changes in version 5.005
    perl5004delta	Perl changes in version 5.004
    perlfaq		Perl frequently asked questions
    perltoc		Perl documentation table of contents

    perldata		Perl data structures
    perlsyn		Perl syntax
    perlop		Perl operators and precedence
    perlre		Perl regular expressions
    perlrun		Perl execution and options
    perlfunc		Perl builtin functions
    perlopentut		Perl open() tutorial
    perlvar		Perl predefined variables
    perlsub		Perl subroutines
    perlmod		Perl modules: how they work
    perlmodlib		Perl modules: how to write and use
    perlmodinstall	Perl modules: how to install from CPAN
    perlform		Perl formats
    perlunicode		Perl unicode support
    perllocale		Perl locale support

    perlreftut		Perl references short introduction
    perlref		Perl references, the rest of the story
    perldsc		Perl data structures intro
    perllol		Perl data structures: arrays of arrays
    perlboot		Perl OO tutorial for beginners
    perltoot		Perl OO tutorial, part 1
    perltootc		Perl OO tutorial, part 2
    perlobj		Perl objects
    perltie		Perl objects hidden behind simple variables
    perlbot		Perl OO tricks and examples
    perlipc		Perl interprocess communication
    perlfork		Perl fork() information
    perlthrtut		Perl threads tutorial
    perllexwarn		Perl warnings and their control
    perlfilter		Perl source filters
    perldbmfilter	Perl DBM filters

    perlcompile		Perl compiler suite intro
    perldebug		Perl debugging
    perldiag		Perl diagnostic messages
    perlnumber		Perl number semantics
    perlsec		Perl security
    perltrap		Perl traps for the unwary
    perlport		Perl portability guide
    perlstyle		Perl style guide

    perlpod		Perl plain old documentation
    perlbook		Perl book information

    perlembed		Perl ways to embed perl in your C or C++ application
    perlapio		Perl internal IO abstraction interface
    perldebguts		Perl debugging guts and tips
    perlxs		Perl XS application programming interface
    perlxstut		Perl XS tutorial
    perlguts		Perl internal functions for those doing extensions
    perlcall		Perl calling conventions from C
    perlapi		Perl API listing (autogenerated)
    perlintern		Perl internal functions (autogenerated)

    perltodo		Perl things to do
    perlhack		Perl hackers guide
    perlhist		Perl history records

    perlamiga		Perl notes for Amiga
    perlcygwin		Perl notes for Cygwin
    perldos		Perl notes for DOS
    perlhpux		Perl notes for HP-UX
    perlmachten		Perl notes for Power MachTen
    perlos2		Perl notes for OS/2
    perlos390		Perl notes for OS/390
    perlvms		Perl notes for VMS
    perlwin32		Perl notes for Windows

(If you're intending to read these straight through for the first time,
the suggested order will tend to reduce the number of forward references.)

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

Extensive additional documentation for Perl modules is available.  The
default configuration for perl will place this additional documentation
in the F</usr/local/lib/perl5/man> directory (or else in the F<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 F</usr/local/man/man1>
and F</usr/local/man/man3>, you need only to add that stem
(F</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 F<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 B<-w> switch first.  It
will often point out exactly where the trouble is.

=head1 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, 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 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 B<sed> or B<awk> or
B<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 B<sed> and B<awk>
scripts into Perl scripts.

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

=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<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>, L<perltoot>, and L<perlbot>.

=item * compilability into C code or Perl bytecode

Described in L<B> and L<B::Bytecode>.

=item * support for light-weight processes (threads)

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

=item * support for internationalization, localization, and Unicode 

Described in L<perllocale> and L<utf8>.

=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<perldebug>.

=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

 a2p	awk to perl translator
 s2p	sed to perl translator

 http://www.perl.com/	    the Perl Home Page
 http://www.perl.com/CPAN   the Comprehensive Perl Archive

=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.com .  If you've succeeded
in compiling perl, the B<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.