Perl Modules

1
Perl Modules
2
Perl Modules

• Namespaces are the mechanism using which you will
  create modules, libraries, classes and objects.
• Name spaces are places to segregate code so that
  one segment of code does not conflict with
  another functions and variables live in a
  name space.
• A Package is a group of perl code that exists
  within its own namespace.
• A module is a reusable package placed in a
  separate file under the same name as the package
  name and a.pm extension.
• Perl implements a class using a package, but the
  presence of a package doesn't imply the presence
  of a class.
• A class is a package that provides subroutines
  that can be used as methods.
• Modules are included into scripts via use module.
• Libraries are similar to modules, but are
  included in the application while the program is
  running.
• One namespace per file and one file per
  namespace.

3
Some well-known modules

• CGI - web programming
• CGI.pm is the most used module for CGI scripts.
• CGI.pm makes programmer's life easy, without
  making him bother much about the HTML tags .
• DBI - common database interface
• DBI is a database access Application Programming
  Interface (API) for the Perl Language. The DBI
  API Specification defines a set of functions,
  variables and conventions that provide a
  consistent database interface independant of the
  actual database being used. In simple language,
  the DBI interface allows users to access multiple
  database types transparently.
• The DBI requires one or more driver modules to
  talk to databases. Oracle, Access and ODBC
  drivers might be of interest to us.
• GUI - interfaces to GUI toolkits
• Perl also provides modules for various GUI
  toolkits on Unix like Gtk, Tk, XForms etc. A beta
  version for Win32 GUI is also available.

4

• There are two special subroutines called BEGIN
  and END that act as constructors and destructors
  in a package.
• A BEGIN subroutine is executed as soon as
  possible even before the rest of the file is
  parsed.
• Multiple BEGIN blocks are allowed in a file and
  execute in the order of definition.
• An END subroutine is executed as late as possible
  (when the interpreter is being exited).
• Multiple END blocks are allowed in a file and
  execute in the reverse order of definition.

5
use

• Modules are included into scripts via use module.
• All modules that are included in the scripts are
  syntax-checked and then executed.
• Example
• if (flag eq On)
• use ModuleOne
• else
• use ModuleTwo
• Will translate into
• use ModuleOne
• use ModuleTwo
• if (flag eq On)
• else

6
To write a Simple moduleTwo ways

• Simple.pm
• package Simple
• sub True return (1)
• sub False return (0)
• 1
• Client.pl
• use Simple
• print SimpleTrue()

• Simple.pm
• package Simple
• use Exporter
• _at_ISA qw(Exporter)
• _at_EXPORT qw (True)
• sub True return (1)
• sub False return (0)
• 1
• Client.pl
• use Simple
• print True()

7

• Modules with use.
• Write a perl script that has a .pm suffix, for
  example, Employee.pm.
• The package name is Employee in the Employee.pm.
• To use Employee.pm in a program called
  EmployeeDemo,
• include use Employee
• Use is done at compile time.

8

• Employee.pm
• package Employee
• Sub new

• EmployeeDemo.pl
• use Employee
• emp1 Employee-gtnew()

9
Objects

• package Student in file Student.pm
• sub new A constructor that returns a blessed
• reference.
• my self the object is created as
  an
• anonymous hash
• self-gtNAME undef
• self-gtMAJOR undef
• bless makes and returns the object to the
  function
• that called it.
• bless(self) return self
• sub name
• my self shift
• if (_at__) self-gtNAME shift
• return self-gtNAME
• sub major
• my self shift
• if (_at__) self-gtMAJOR shift
• return self-gtMAJOR

10

• ! /usr/local/bin/perl -w
• use Student
• one Student-gtnew() Create one Student object
• one-gtname("Smith")
• one-gtmajor("COEN")
• printf "Name s Major s \n", one-gtname,
  one-gtmajor

11

• !/usr/local/bin/perl -w
• package Course
• sub new
• my(type,args) _at__ type or class is
• always passed as the first parameter
• my self
• self-gtNAME args
• return bless(self,type)
• sub name
• my self shift
• return self-gtNAME
• 1

12

• package Course
• sub new
• my(type) shift
• my self
• self-gtNAME shift
• self-gtUNITS shift
• the two argument bless should be used if
• this class is to be used as a parent class
• return bless(self,type)
• an alternate way of passing parameters
• to bless is
• return bless (self, ref(type) (type)

13

• ! /usr/local/bin/perl -w
• use Course
• c Course-gtnew(COEN276,4)
• d c-gtnew (coen176,4) the class is derived
  using the ref() from the object.

14
Inheritance ISA relationship

• !/usr/local/bin/perl -w
• package GradCourse
• use Course
• _at_ISA qw(Course)
• create base object and extend with new
  properties
• sub new
• my (class,name, units,project) _at__
• my self Course-gtnew(name,units)
• self-gtPROJECT project
• return bless self, class
• sub getProject
• my self shift
• return self-gtproject
• sub name
• my self shift
• my fullTitle self-gtSUPERname() .
  "_G"
• return fullTitle