code ways to share programs sharing code shifting argument parsing parsing shifting style @_ array removing items from eval function syntax errors $@ variable subroutines syntax errors and eval function do operator variables my variables my variables lexical variables defined scope do operator and .plx (Perl Executable) extension .pl (Perl Library) extension warnings, enabling require operator functionality libraries loading only once require operator syntax errors and syntax errors $@ variable require operator functionality @INC array require operator and require operator @INC and current directory search path and search path libraries search path for PATH environment variable current directory @INC array and perl command -V command line option push function unshift function PERL5LIB environment variable directories separating with colon : (colon) perl command -I option collisions, namespace namespaces problems with collisions prefixes, explicit namespaces packages as separators packages as namespace separators _ (underscore) packages naming considerations modules core modules core modules :: (double colon) filehandles package names and subroutines package names and hashes package names and arrays package names and scalars package names and packages main program in packages scope of directives variables my variables my variables packages scope of directives packages global variables variables global variables global variables package variables as lexical variables packages and packages lexicals and lexical variables packages and packages lexicals and hashes scalars and ordered lists arrays scalars and arrays ordered lists and scalars single values and references overview grep operator scalar context and shifting @_ array parsing shifting style shifting argument parsing @_ array creating @_ array changes reflected passing by reference references \ (backslash) "take a reference to" operator references array reference blessed references dereferencing hash reference also array reference blessed references dereferencing hash reference arrays referencing scalars references and hashes references and variables memory addresses of memory addresses hexadecimal memory address ARRAY(0x1a2b3c) array reference features array reference features arrays referencing arrays referencing {} (curly braces) arrays and array reference dereferencing dereferencing array references arrays curly braces programs whitespace whitespace @_ array dereferencing and code decoupling arrays referencing shifting example eliminating array reference dereferencing dereferencing array references array reference curly braces and {} (curly braces) dropping {} (curly braces) dropping array reference curly braces and array reference modifying arrays modifying arrays dereferencing and arrays modifying array reference modifying @_ array nested data structures arrays nested data structures and nested entities data structures data structures nested array reference nested data structures dereferencing array references array reference dereferencing nested entities data structures data structures nested array reference arrows and nested entities element references {} (curly braces) dereferencing arrows drop arrow rule drop arrow rule array reference arrows and "take a reference to" operator \ (backslash) hash reference features dereferencing hash references hash reference dereferencing {} (curly braces) hashes and arrows hash references and arrows hash references and hexadecimal memory address HASH(0x1a2b3c) memory addresses hash reference as parameters parameters hash references as data structures references to anonymous scope references and references scoping and reference counting defined @_ array references and scoping lexical variables reference longevity variables reference removal and anonymous arrays defined dereferencing array references array reference dereferencing arrays dereferencing and variables reference removal and data structures nested nested entities data structures reference counting nested data structures and memory management reference counting memory management and looping (data structure) data structures looping and looping (data structure) data structures looping and reference counting garbage collection and garbage collection arrays anonymous arrays also anonymous arrays anonymous arrays creating directly arrays scoping considerations anonymous arrays square brackets and [] (square brackets) constructors anonymous array array reference anonymous array constructors and () (parentheses) [] (square brackets) array reference anonymous array constructors and constructors anonymous array anonymous hash creating hash reference anonymous hash constructors anonymous arrays hash references and constructors anonymous hash {} (curly braces) anonymous hash constructors constructors anonymous hash scalars hash references and , (comma) constructors anonymous hash key/value pairs ; (semicolon) + (plus sign) autovivification process defined programs whitespace whitespace array reference empty arrays and undef (value) autovivification and hash reference autovivification and autovivification hash references and # (pound sign) comments data structures manipulating complex data structures data structures viewing data with debugger data viewing with debugger debugging viewing complex data perl command -d option s command (debugger) debugging x command x command (debugger) hash reference debugging example hash reference debugging example looping (code structure) hash reference debugging example viewing data Data::Dumper data viewing with Data::Dumper Data::Dumper module debugging x command x command (debugger) Dumper subroutine hash reference Data::Dumper example viewing data Data::Dumper data viewing with Data::Dumper Data::Dumper module data storing storing data Storable module map operator functionality grep operator functionality testing expression (of map or grep) grep operator scalar context and block form grep operator expression form grep operator block form map operator expression form map operator testing expression (of map or grep) map operator scalar context hashes map operator and indirection applying grep operator indirection and map operator indirection and data selecting grep operator selecting complex data array reference hashes into hashes references and constructors anonymous array map operator selecting complex data map operator Schwartzian Transform also Schwartzian Transform grep operator Schwartzian Transform also Schwartzian Transform data selecting anonymous arrays complex data and data structures references to subroutines variables as repository of values behavior subroutine references and programs behaviors of code references overview subroutine references references named subroutines subroutines referencing "take a reference to" operator \ (backslash) & (ampersand) () (parentheses) dereferencing coderefs {} (curly braces) coderefs and scalars curly braces and dereferencing coderefs anonymous subroutines anonymous subroutines callbacks subroutine references and File::Find module features find subroutine (File::Find) filesystems walking through hierarchy filesystems walking through hierarchy behavior passing as parameter callbacks subroutine references and find subroutine (File::Find) files find subroutine File::Find module features closures functionality working directory current directory search path current directory search path and current directory find( ) function and callbacks find( ) function and lexical variables subroutine references dereferencing lexical variables and current directory find( ) function and callbacks find( ) function and variables out of scope callbacks accessing variables variables callbacks and subroutines closures also closures lexical variables closures and ; (semicolon) scalars anonymous variables out of scope return values subroutine references lexical variables subroutine references variables out of scope reference counting closures and variables callbacks and parameters callbacks and callbacks accessing variables parameters callbacks and variables out of scope callbacks invoking subroutines multiple times reference counting subroutine reference example shifting closure variables variables out of scope scope global variables and closures scope and packages global variables variables global variables global variables scope and closures lexical variables and lexical variables closures and lexical variables subroutine references variables out of scope subroutines out of scope variables and variables static local static local variables variables closure variables closure variables closures persistence and data storing storing data run phase storage allocation compile phase declarations during programs run phase programs compile phase undef (value) variables with value of BEGIN block purpose compile phase BEGIN keyword and run phase BEGIN keyword and looping (code structure) return values coderefs as File::Find module returning coderefs files finding timestamps timestamps () (parentheses) daylight savings time (DST) text strings sorting sorting review of numbers sorting sorting sort blocks numbers sorting <=> (spaceship operator) spaceship operator sorting review of text strings cmp operator cmp operator grep operator indices and sorting with indices indices, sorting with indirection sorting indices sorting with indices indices, sorting with sorting efficient array reference efficient sorting example sorting Schwartzian Transform Schwartzian Transform sorting and array reference Schwartzian Transform references hierarchical data and data structures recursively defined iteration versus recursion directories represented as hashes hashes directories as filesystems capturing information about recursively defined data undef (value) filesystem capture example hash reference as return values return values hash references return values undef example hash reference filesystem capture example hashes anonymous hash also anonymous hash anonymous hash filesystem capture example Data::Dumper module sorting glob operator glob operator sorting dictionary order Schwartzian Transform dictionary order OOP (object-oriented programming) overview programs OOP also OOP object-oriented programming OOP code OOP also OOP use strict arrows method invocation arrow methods invocation arrow behavior classes and classes defined variables package names packages naming considerations arrows method invocation arrow methods invocation arrow parameters method invocation and methods parameters and parameters method invocation and methods parameters and inheritance method invocation and methods inheritance and parameters shifting shifting arguments inheritance method invocation and methods inheritance and @ISA variable features inheritance @ISA variable and AUTOLOAD method inheritance and UNIVERSAL class inheritance and use strict lexical variables @ISA and packages @ISA variable and packages @ISA variable and our variables variables our variables use base compile phase use base and @ISA variable features overriding methods methods overriding code reusability of inheritance code reusability through superclasses SUPER pseudo-class @_ array passing uninterrupted parameters @_ arguments parameters parameters shifting shifting arguments arrows method invocation arrow methods invocation arrow instances defined classes instances and variables member variables member variables variables instance variables lexical variables scalars also instance variables lexical variables scalars instance variables defined properties, instances and behavior instances and references instances and references instances and references bless operator variables bless operator objects bless operator and instances defined objects instances and methods instances and instance methods invoking instances blessed references and blessed references instances as parameters instance methods and instances blessed references and blessed references instances as methods instances and instance methods invoking instance methods class methods and class methods instance methods and parameters instances as data accessing for instances @_ array accessing instance data class methods building instances parameters return values also return values return values parameters also parameters return values bless operator and references return values blessed references returning instances building constructors creating instances new method creating objects objects creating modules core modules core modules inheritance constructors and constructors inheriting inheritance constructors and constructors inheriting references instances and instances methods working with classes methods working with methods working with classes undef (value) ref operator and blessed references ref operator and text strings ref operator and ref operator ?: operator methods parameters and parameters adding to methods instance methods parameters and methods class methods instance methods also class methods instance methods instance methods APIs and API (Application Programming Interface) methods parameters and parameters adding to methods hashes instances and instances hashes and variables member variables member variables instance variables hash keys objects as blessed references blessed references instances as references instances and backstop method objects structure considerations setters creating parameters returning updated values return values updated parameters wantarray function void context void context wantarray function void context objects encapsulation of encapsulation, object setters encapsulation and getters encapsulation and setters optimizing getters optimizing methods getters doubling as setters setters getters doubling as setters optimizing getters doubling as setters setters getters doubling as setters restricting methods getters doubling as setters instance methods restricting to class methods restricting to methods restricting ref operator objects destruction of references object destruction and hash reference object destruction filehandles temporary files temporary files data destruction and instance variables object destruction and DESTROY method purpose DESTROY method purpose programs object destruction and variables global variables global variables data destruction and lexical variables data destruction and END blocks destructors nested objects example DESTROY method nested objects blessed references nested object destruction nested entities object destruction array reference blessing + (plus sign) temporary files data destruction and instance variables filehandles as filehandles instance variables temporary files data destruction and inheritance DESTROY method and DESTROY method inheritance and extending superclass methods overriding superclass methods methods superclasses superclasses inheritance DESTROY method and DESTROY method inheritance and extending superclass methods overriding superclass methods methods superclasses superclasses indirect object notation arrows method invocation arrow methods invocation arrow direct object syntax new method indirect object notation {} (curly braces) indirect object syntax and scalars indirect object syntax blessed references indirect object syntax and perl command -w option direct object syntax instance variables in subclasses subclasses instance variables in subroutines extending extending subroutines superclasses parameters passing to superclasses friend classes inheritance composition versus composition, inheritance versus delegation instance variables in subclasses subclasses instance variables in variables class variables class variables extending class variables variables meta-variables meta-variables destructors class variables and references weak references weak references references destruction and reference counting weak references and WeakRef module memory management undef (value) weak references and parent-child relationships @ISA variable inheritance hierarchies and classes UNIVERSAL class and UNIVERSAL class purpose of backstop method overriding UNIVERSAL class methods methods UNIVERSAL class and behavior testing with isa and can methods testing isa and can methods can method (UNIVERSAL) isa method (UNIVERSAL) UNIVERSAL class utility methods objects testing with isa and can methods inheritance isa method testing instances isa method testing scalars isa method and blessed references isa method and subroutines isa called as behavior testing with isa and can methods testing isa and can methods can method (UNIVERSAL) isa method (UNIVERSAL) UNIVERSAL class utility methods objects testing with isa and can methods AUTOLOAD method functionality $AUTOLOAD variable compile phase AUTOLOAD and AUTOLOAD method functionality modules core modules core modules SelfLoader core module AutoLoader core module setters AUTOLOAD method and getters AUTOLOAD method and accessors AUTOLOAD method and AUTOLOAD method accessors and code references AUTOLOAD method and glob operator AUTOLOAD method accessors and setters AUTOLOAD method and getters AUTOLOAD method and accessors AUTOLOAD method and accessors Class::MethodMaker module Class::MethodMaker module setters creating getters creating easily abstract methods subclasses abstract methods and methods abstract methods classes accessors and instances accessors and friend classes maintenance considerations interfaces maintenance considerations system performance inheritance multiple inheritance @ISA variable multiple inheritance references to filehandles filehandles references to IO::File class variables filehandles and objects filehandles and scalars filehandles and destructors IO::File objects and glob operator IO::File class array reference IO::File objects and grep operator filehandles and grep operator filehandles and modules overview modules packages also packages packages modules also modules variables modules and subroutines modules and code reusability of parsing file specifications files parsing specifications interfaces File::Basename module File::Basename module dirname subroutine (File::Basename) basename subroutine (File::Basename) fileparse subroutine (File::Basename) interfaces File::Basename module File::Basename module importing File::Basename module and qw( ) list lists qw( ) list empty import lists lists absent import lists absent import lists & (ampersand) interfaces File::Spec module OOP (object-oriented programming) File::Spec module File::Spec module files File::Spec module class methods File::Spec module and catfile method (File::Spec) collisions, namespace namespaces problems with collisions Math::BigInt module Math::BigInt module new method Math::BigInt module instance methods Math::BigInt module OOP (object-oriented programming) versus non-OOP OO (object-oriented) modules non-OO versus instance methods OO modules and class methods OO modules and exporting OO modules and importing use operation and BEGIN block use list and require operator use operation and use operation :: (double colon) .pm (Perl Module) extension require operator use operation and return values required files subroutines importing importing subroutines BEGIN block importing subroutines @INC array use operation and paths, searching for installed modules/libraries BEGIN block setting paths unshift function use lib use lib constants, setting BEGIN block setting constants paths, searching for installed modules/libraries File::Basename module fileparse subroutine (File::Basename) importing Exporter module and Exporter module importing with symbols importing Exporter module and Exporter module importing with Exporter module package variables @EXPORT variable @EXPORT_OK variable @EXPORT_OK variable subroutines importing importing subroutines @EXPORT variable exporting OO modules and OO (object-oriented) modules exporting and Exporter module importing with export_fail method (Exporter) require_version method (Exporter) export_to_level method (Exporter) unimport method (Exporter) URI::URL module URIs (universal resource identifiers) url subroutine (URI::URL) constructors url subroutine CGI module importing custom routines subroutines custom import routines use CGI importing -nosticky option writing distributions installation (of modules) distribution considerations documentation distribution considerations archiving testing distributions and interfaces distribution considerations modules distributions and distributions h2xs tool h2xs tool distributions and distributions template files files distribution templates template files MANIFEST file MANIFEST file README file distributions copyrights and licensing licensing copyright notices README file Changes file debugging Changes file and distributions modules within modules distributions and distributions Exporter module Exporter module distributions distributions qw( ) lists qw( ) list lists qw( ) list exporting symbols symbols @EXPORT variable @EXPORT_OK variable exporting OO modules and OO (object-oriented) modules exporting distributions version numbers version numbers interfaces version numbers and CPAN (Comprehensive Perl Archive Network) version numbers and use operation _ _END_ _ marker distributions embedded documentation documentation embedded for distribution distributions POD format POD format Makefile.PL controlling distribution distributions Makefile.PL perl command -V:make h2xs tool Makefile.PL and ExtUtils::MakeMaker module WriteMakefile subroutine (ExtUtils::MakeMaker) PREREQ_PM setting (Makefiles) distributions alternate installation locations installation (of modules) alternate locations perl command PREFIX= option (Makefile.PL) Makefile.PL PREFIX=option libraries alternate installation locations scripts alternate installation locations make test distributions testing testing distributions and testing test harness Makefile.PL test harness make install distributions make dist and make dist $VERSION variable distributions make dist and make dist installation (of modules) alternate library locations libraries alternate installation locations perl command PREFIX= option (Makefile.PL) Makefile.PL PREFIX=option use lib perl command -M option perl command -I option distributions testing make test documentation testing and testing sqrt function sqrt function code testing coverage testing code coverage Makefile.PL test harness testing test harness directories t files and t directory testing test harness Makefile.PL test harness distributions Test::Simple module Test::Simple module ok function (Test::Simple) TEST_VERBOSE option (make test) make test comments testing pound-sign comments and # (pound sign) distributions Test::Simple module Test::Simple module distributions Test::More module Test::More module testing test harness Makefile.PL test harness is function (Test::More) testing numeric equality numbers testing equality testing inequality isnt function (Test::More) cmp_ok routine (Test::More) like function (Test::More) strings text strings text strings like function can_ok function (Test::More) isa_ok function (Test::More) OO (object-oriented) modules Test::More module testing use operation use operation BEGIN block use operation and use operation conditional tests testing conditional tests $TODO variable TODO blocks testing multiple test scripts scripts complex tests h2xs tool multiple test scripts and STDERR filehandle STDOUT filehandle filehandles ok function (Test::More) and Test::More module ok function (Test::Simple) testing writing to STDOUT and STDERR temporary files STDOUT and is function (Test::More) current directory testing and Comprehensive Perl Archive Network CPAN CPAN (Comprehensive Perl Archive Network) contributing to perl-packrats mailing list PAUSE (Perl Authors Upload Server) ID distributions preparing README file Makefile.PL testing and testing Makefile.PL and MANIFEST file version numbers distributions version numbers distributions preparing PAUSE (Perl Authors Upload Server) ID distributions uploading to CPAN distributions uploading to CPAN distributions announcing CPAN modules modules announcing testing smoke tests smoke tests scalars references and references as scalars perl command -w option debugging enabling warnings during warnings, enabling lists sorted list sorting sorted list Schwartzian Transform performance OOP (object-oriented programming) inheritance structures and classes virtual methods and data storing storing data dbmopen function = operator filehandles || operator and filehandles storing in a hash hashes storing filehandles ||= operator || operator