perl - Practical Extraction and Report Language

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

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 dataif 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.

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.

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

    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

    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

    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

    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
    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

    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)

    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
    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

On Debian systems, you need to install the perl-doc package which contains the majority of the standard Perl documentation and the perldoc program.

Extensive additional documentation for Perl modules is available, both those distributed with Perl and third-party modules which are packaged or locally installed.

You should be able to view Perl's documentation with your man(1) program or perldoc(1).

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.

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.

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

See perlrun.

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 .

 "@INC"                 locations of perl libraries

 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 Media)
 http://www.cpan.org/       the Comprehensive Perl Archive
 http://www.pm.org/         the Perl Mongers

The CWuse warnings pragma (and the -w switch) produces some lovely diagnostics.

See perldiag for explanations of all Perl's diagnostics. The CWuse 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?

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 CWperl -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.

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.