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# perl

Perl 5 version 12.2 documentation
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# perl

- NAME
- SYNOPSIS
- GETTING HELP
  - Overview
  - Tutorials
  - Reference Manual
  - Internals and C Language Interface
  - Miscellaneous
  - Language-Specific
  - Platform-Specific
- DESCRIPTION
- AVAILABILITY
- ENVIRONMENT
- AUTHOR
- FILES
- SEE ALSO
- DIAGNOSTICS
- BUGS
- NOTES

# NAME

perl - The Perl language interpreter

# SYNOPSIS

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

# GETTING HELP

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

If you're new to Perl, you should start by running `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 `perldoc perldoc` to learn more things you can do with perldoc.

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

## 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    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

## 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    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 Version 5.2.0 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    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    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    perlpolicy		Perl development policies    perlrepository	Perl source repository

## Miscellaneous

        perlbook		Perl book information    perlcommunity	Perl community information    perltodo		Perl things to do    perldoc		Look up Perl documentation in Pod format    perlhist		Perl history records    perldelta		Perl changes since previous version    perl5121delta	Perl changes in version 5.12.1    perl5120delta	Perl changes in version 5.12.0    perl5115delta	Perl changes in version 5.11.5    perl5114delta	Perl changes in version 5.11.4    perl5113delta	Perl changes in version 5.11.3    perl5112delta	Perl changes in version 5.11.2    perl5111delta	Perl changes in version 5.11.1    perl5110delta	Perl changes in version 5.11.0    perl5101delta	Perl changes in version 5.10.1    perl5100delta	Perl changes in version 5.10.0    perl595delta	Perl changes in version 5.9.5    perl594delta	Perl changes in version 5.9.4    perl593delta	Perl changes in version 5.9.3    perl592delta	Perl changes in version 5.9.2    perl591delta	Perl changes in version 5.9.1    perl590delta	Perl changes in version 5.9.0    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    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    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    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    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    perlriscos		Perl notes for RISC OS    perlsolaris 	Perl notes for Solaris    perlsymbian 	Perl notes for Symbian    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

On a Unix-like system, these documentation files will usually also be available as manpages for use with the 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 -w switch first. It will often point out exactly where the trouble is.

# DESCRIPTION

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

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 <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 .

# 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 perlbug@perl.org . 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.

Page index

- NAME
- SYNOPSIS
- GETTING HELP
  - Overview
  - Tutorials
  - Reference Manual
  - Internals and C Language Interface
  - Miscellaneous
  - Language-Specific
  - Platform-Specific
- DESCRIPTION
- AVAILABILITY
- ENVIRONMENT
- AUTHOR
- FILES
- SEE ALSO
- DIAGNOSTICS
- BUGS
- NOTES