Link : http://www.tutorialspoint.com/perl/perl_modules.htm
Below is my code -
******************
Package name - Foo.pm
#!/usr/bin/perl
require Foo;
Foo::bar( "a" );
Foo::blat( "b" );
yatendra@yatendra:~/Research$ cat Foo.pm
##!/usr/bin/perl
package Foo;
sub bar {
print "Hello $_[0]\n"
}
sub blat {
print "World $_[0]\n"
}
1;
******************
File name - Perl.pl
#!/usr/bin/perl
require Foo;
Foo::bar( "a" );
Foo::blat( "b" );
******************
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Below is my code -
******************
Package name - Foo.pm
#!/usr/bin/perl
require Foo;
Foo::bar( "a" );
Foo::blat( "b" );
yatendra@yatendra:~/Research$ cat Foo.pm
##!/usr/bin/perl
package Foo;
sub bar {
print "Hello $_[0]\n"
}
sub blat {
print "World $_[0]\n"
}
1;
******************
File name - Perl.pl
#!/usr/bin/perl
require Foo;
Foo::bar( "a" );
Foo::blat( "b" );
******************
Create the Perl Module Tree
h2xs -AX -n Foo ******************
What are Packages?
- A package is a collection of code which lives in its own namespace
- A namespace is a named collection of unique variable names (also called a symbol table).
- Namespaces prevent variable name collisions between packages
- Packages enable the construction of modules which, when used, won't clobbber variables and functions outside of the modules's own namespace
The Package Statement
- package statement switches the current naming context to a specified namespace (symbol table)
- If the named package does not exists, a new namespace is first created.
$i = 1; print "$i\n"; # Prints "1" package foo; $i = 2; print "$i\n"; # Prints "2" package main; print "$i\n"; # Prints "1" |
- The package stays in effect until either another package statement is invoked, or until the end of the end of the current block or file.
- You can explicitly refer to variables within a package using the :: package qualifier
$PACKAGE_NAME::VARIABLE_NAME For Example: $i = 1; print "$i\n"; # Prints "1" package foo; $i = 2; print "$i\n"; # Prints "2" package main; print "$i\n"; # Prints "1" print "$foo::i\n"; # Prints "2" |
BEGIN and END Blocks
You may define any number of code blocks named BEGIN and END which act as constructors and destructors respectively.BEGIN { ... }
END { ... }
BEGIN { ... }
END { ... }
|
- Every BEGIN block is executed after the perl script is loaded and compiled but before any other statement is executed
- Every END block is executed just before the perl interpreter exits.
- The BEGIN and END blocks are particularly useful when creating Perl modules.
What are Perl Modules?
A Perl module is a reusable package defined in a library file whose name is the same as the name of the package (with a .pm on the end).A Perl module file called "Foo.pm" might contain statements like this.
#!/usr/bin/perl
package Foo;
sub bar {
print "Hello $_[0]\n"
}
sub blat {
print "World $_[0]\n"
}
1;
|
- The functions require and use will load a module.
- Both use the list of search paths in @INC to find the module (you may modify it!)
- Both call the eval function to process the code
- The 1; at the bottom causes eval to evaluate to TRUE (and thus not fail)
The Require Function
A module can be loaded by calling the require function#!/usr/bin/perl require Foo; Foo::bar( "a" ); Foo::blat( "b" ); |
It would be nice to enable the functions bar and blat to be imported into our own namespace so we wouldn't have to use the Foo:: qualifier.
The Use Function
A module can be loaded by calling the use function#!/usr/bin/perl use Foo; bar( "a" ); blat( "b" ); |
The use function will export a list of symbols from a module given a few added statements inside a module
require Exporter; @ISA = qw(Exporter); |
package Module;
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(bar blat);
sub bar { print "Hello $_[0]\n" }
sub blat { print "World $_[0]\n" }
sub splat { print "Not $_[0]\n" } # Not exported!
1;
|
Create the Perl Module Tree
When you are ready to ship your PERL module then there is standard way of creating a Perl Module Tree. This is done using h2xs utility. This utility comes alongwith PERL. Here is the syntax to use h2xs$h2xs -AX -n Module Name # For example, if your module is available in Person.pm file $h2xs -AX -n Person This will produce following result Writing Person/lib/Person.pm Writing Person/Makefile.PL Writing Person/README Writing Person/t/Person.t Writing Person/Changes Writing Person/MANIFEST |
- -A omits the Autoloader code (best used by modules that define a large number of infrequently used subroutines)
- -X omits XS elements (eXternal Subroutine, where eXternal means external to Perl, i.e. C)
- -n specifies the name of the module
- Changes
- Makefile.PL
- MANIFEST (contains the list of all files in the package)
- README
- t/ (test files)
- lib/ ( Actual source code goes here
Installing Perl Module
Installing a Perl Module is very easy. Use the following sequence to install any Perl Module.perl Makefile.PL make make install
