Advanced Perl Programming

Modules

1. The package keyword starts a new namespace (which lasts until another package declaration or until end of block). All user-defined global identifiers (variables, subroutines, filehandles) belong to this package. Lexical variables do not belong to any package.

   package Employee; # Put in file Employee.pm
   @employees = ("John", "Fred", "Mary", "Sue");
   sub list_employee { print @employees; }
   1;                # Last executing statement in file must be 
                     # non-zero, to indicate successful loading

2. To load module Employee:

   use Employee;
   #or 
   require Employee;

   Specify the load path with the -I command-line option, PERL5LIB environment variable, or @INC.

3. Access foreign package’s variables and subroutines with fully qualified names:

   print @Employee::employees;    
   Employee::print();

   Privacy is not enforced.

4. If a subroutine is not found in that package, a default subroutine AUTOLOAD() is called, if present. $AUTOLOAD is set to the fully qualified name of the missing subroutine.

5. To inherit module C from modules A and B, prime C’s @ISA array with the names of its superclass modules:

   package A;
   sub foo{ print "A::foo called \n";}
   package C;
   @ISA = ("A", "B");
   C->foo();               # Calls A::foo, because B does not