PERL(1)								      PERL(1)



NAME
  perl - Practical Extraction and Report Language

SYNOPSIS
  For ease of access, the Perl manual has been split up into a number of
  sections:

      perl	  Perl overview (this section)
      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
      perlvar	  Perl predefined variables
      perlsub	  Perl subroutines
      perlmod	  Perl modules
      perlref	  Perl references and nested data structures
      perlobj	  Perl objects
      perlbot	  Perl OO tricks and examples
      perldebug	  Perl debugging
      perldiag	  Perl diagnostic messages
      perlform	  Perl formats
      perlipc	  Perl interprocess communication
      perlsec	  Perl security
      perltrap	  Perl traps for the unwary
      perlstyle	  Perl style guide
      perlapi	  Perl application programming interface
      perlguts	  Perl internal functions for those doing extensions
      perlcall	  Perl calling conventions from C
      perlovl	  Perl overloading semantics
      perlbook	  Perl book information

  (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.)

  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 an interpreted 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).	It
  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 quite 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 hash tables used by associative
  arrays grow as necessary to prevent degraded performance.  Perl uses
  sophisticated pattern matching techniques to scan large amounts of data
  very quickly.	 Although optimized for scanning text, Perl can also deal
  with binary data, and can make dbm files look like associative arrays
  (where dbm is available).  Setuid Perl scripts are safer than C programs
  through a dataflow tracing mechanism which 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...

  Perl version 5 is nearly a complete rewrite, and provides the following
  additional benefits:

  + Many usability enhancements
       It is now possible to write much more readable Perl code (even within
       regular expressions).  Formerly cryptic variable names can be replaced
       by mnemonic identifiers.	 Error messages are more informative, and the
       optional warnings will catch many of the mistakes a novice might make.
       This cannot be stressed enough.	Whenever you get mysterious behavior,
       try the -w switch!!!  Whenever you don't get mysterious behavior, try
       using -w anyway.

  + Simplified grammar
       The new yacc grammar is one half the size of the old one.  Many of the
       arbitrary grammar rules have been regularized.  The number of reserved
       words has been cut by 2/3.  Despite this, nearly all old Perl scripts
       will continue to work unchanged.

  + Lexical scoping
       Perl variables may now be declared within a lexical scope, like "auto"
       variables in C.	Not only is this more efficient, but it contributes
       to better privacy for "programming in the large".

  + Arbitrarily nested data structures
       Any scalar value, including any array element, may now contain a
       reference to any other variable or subroutine.  You can easily create
       anonymous variables and subroutines.  Perl manages your reference
       counts for you.

  + Modularity and reusability
       The Perl library is now defined in terms of modules which can be
       easily shared among various packages.  A package may choose to import
       all or a portion of a module's published interface.  Pragmas (that is,
       compiler directives) are defined and used by the same mechanism.

  + Object-oriented programming
       A package can function as a class.  Dynamic multiple inheritance and
       virtual methods are supported in a straightforward manner and with
       very little new syntax.	Filehandles may now be treated as objects.

  + Embeddible and Extensible
       Perl may now be embedded easily in your C or C++ application, and can
       either call or be called by your routines through a documented
       interface.  The XS preprocessor is provided to make it easy to glue
       your C or C++ routines into Perl.  Dynamic loading of modules is
       supported.

  + POSIX compliant
       A major new module is the POSIX module, which provides access to all
       available POSIX routines and definitions, via object classes where
       appropriate.


  + Package constructors and destructors
       The new BEGIN and END blocks provide means to capture control as a
       package is being compiled, and after the program exits.	As a
       degenerate case they work just like awk's BEGIN and END when you use
       the -p or -n switches.

  + Multiple simultaneous DBM implementations
       A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
       files from the same script simultaneously.  In fact, the old dbmopen
       interface has been generalized to allow any variable to be tied to an
       object class which defines its access methods.

  + Subroutine definitions may now be autoloaded
       In fact, the AUTOLOAD mechanism also allows you to define any
       arbitrary semantics for undefined subroutine calls.  It's not just for
       autoloading.

  + Regular expression enhancements
       You can now specify non-greedy quantifiers.  You can now do grouping
       without creating a backreference.  You can now write regular
       expressions with embedded whitespace and comments for readability.  A
       consistent extensibility mechanism has been added that is upwardly
       compatible with all old regular expressions.

  Ok, that's definitely enough hype.

ENVIRONMENT

  HOME	      Used if chdir has no argument.

  LOGDIR      Used if chdir has no argument and HOME is not set.

  PATH	      Used in executing subprocesses, and in finding the script if -S
	      is used.

  PERL5LIB    A colon-separated list of directories in which to look for Perl
	      library files before looking in the standard library and the
	      current directory.  If PERL5LIB is not defined, PERLLIB is
	      used.

  PERL5DB     The command used to get the debugger code.  If unset, uses

		      BEGIN { require 'perl5db.pl' }


  PERLLIB     A colon-separated list of directories in which to look for Perl
	      library files before looking in the standard library and the
	      current directory.  If PERL5LIB is defined, PERLLIB is not
	      used.

  Apart from these, Perl uses no other environment variables, except to make
  them available to the script being executed, and to child processes.
  However, scripts running setuid would do well to execute the following
  lines before doing anything else, just to keep people honest:

      $ENV{'PATH'} = '/bin:/usr/bin';	 # or whatever you need
      $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
      $ENV{'IFS'} = ''		if defined $ENV{'IFS'};


AUTHOR
  Larry Wall