Perl 101 for EPrints

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Where to start

Learning Perl: Helping you get started with Perl 5.... http://learn.perl.org/

Perl Tutorials http://perldoc.perl.org/perl.html#Tutorials

Recommended books for learning Perl

Learning Perl, 6th Edition by Randal Schwartz, brian d foy, Tom Phoenix http://www.amazon.com/Learning-Perl-Randal-L-Schwartz/dp/1449303587

Programming Perl: Unmatched power for text processing and scripting Fourth Edition Edition by Tom Christiansen, brian d foy, Larry Wall, Jon Orwant http://www.amazon.com/Programming-Perl-Unmatched-processing-scripting/dp/0596004923/

Intermediate Perl Second Edition Edition by Randal L. Schwartz, brian d foy, Tom Phoenix http://www.amazon.com/Intermediate-Perl-Randal-L-Schwartz/dp/1449393098/

Using Perl in EPrints

Retrieving data from a config file

Example of a data config file under /cfg/cfg.d/example.pl

The data structure is an array of hashes (http://perldoc.perl.org/perldsc.html#ARRAYS-OF-HASHES)

$c->{etd_ms}->{fields} = [
	{ tagname => 'etd_ms:type', type=> 'constant', value => "Electronic Thesis or Dissertation" },
	{ tagname => 'etd_ms:degree', type => 'compound', parts => [
		{ tagname => 'etd_ms:name', type => 'simple_text', eprint_fieldname => 'thesis_degree_name' },
		{ tagname => 'etd_ms:level', type => 'simple_text', eprint_fieldname => 'thesis_type' },
		{ tagname => 'etd_ms:discipline', type => 'simple_text', eprint_fieldname => 'department' },
		{ tagname => 'etd_ms:grantor', type => 'simple_text', eprint_fieldname => 'institution' },
	] },
];

Retrieving values from this config file in an "Example" export plugin under /plugins/EPrints/Plugin/Export/example.pm

               package EPrints::Plugin::Export::Example;
               use EPrints::Plugin::Export;
               @ISA = ( "EPrints::Plugin::Export" );
               [...]
               my $fields = $session->get_conf('etd_ms','fields');					
               foreach my $field_conf (@{$fields})
		{
		   my $tags = $plugin->generate_tag($eprint, $field_conf);			
		   foreach my $tag (@{$tags})
		   {
					push @dcdata, ($tag) if $tag; 
		   }
		}

Supporting function that returns an arrayref

sub generate_tag {
	my ($plugin, $eprint, $field_conf) = @_;
 
	#Constant value
	if ($field_conf->{type} eq 'constant')
	{
		return $plugin->generate_constant_tag($eprint, $field_conf);
	}
}

Supporting function that generates a tag

sub generate_constant_tag{
	my ($plugin, $eprint, $field_conf) = @_;
 
	my $tag = $plugin->_simple_tag($field_conf, $field_conf->{value});
	return [ $tag ];
}

Function parameters

In perl, the following:
$obj->function($arg1, $arg2)
is equivalent to:
Class::function($obj, $arg1,$arg2)

In the example above, when we call:

my $tags = $plugin->generate_tag($eprint, $field_conf);

It is equivalent to:

my $tags = Example::generate_tag($plugin, $eprint, $field_conf);

This explains the three parameters listed in the top of the generate_tag function definition:

sub generate_tag {
my ($plugin, $eprint, $field_conf) = @_;

Tips and tricks

Creating a session

Creating a session with eprints is now done via EPrints->new() however many scripts (and examples still use the legacy EPrints::Session->new() interface.

See "perl_lib/EPrints/BackCompatibility.pm" line 424 for details of the compatibility wrapper and "perl_lib/EPrints.pm" for full usage of Eprints methods.

Old style:

# When using this interface both values are required - 1 (to indicate this is a script not CGI) and repo id (second val). Attempting to run without the repo ID results in the following errors:
# Use of uninitialized value $repository_id in string eq at /usr/share/eprints/perl_lib/EPrints.pm line 551.
# Can't call method "get_database" on an undefined value at /usr/share/eprints/perl_lib/EPrints/DataObj.pm line 132.
 
my $session = EPrints::Session->new( 1, 'REPOID');

New style:

# Note specifying CGI is not required via this interface.
my $ep = EPrints->new( cleanup=>0 );
my $session = $ep->repository( 'epprod');

Usage of get_config

EPrints::Repository::get_config (accessed via $session->get_repository->get_conf()) can be used with two or three parameters.

With only two (key and value) returns a hash $session->get_repository->get_conf( "datacitedoi", "typesallowed")

With three values (key and two values) will return 1 (true) if the last item is found in the list of the second entry - config_entry below $session->get_repository->get_conf( "datacitedoi", "config_entry", 'Thesis')


get_config is a thin wrapper around config()

See also "perl_lib/EPrints/Repository.pm" line 1611

A basic EPrint extracting script

The simplest of examples, use eprints to register a session in the repository then read an (arbitrary) eprint; accessing two bits of information about it. The attributes accessed come from EPrint Object and API:EPrints/DataObj.

#!/usr/bin/perl -w                                                                                                                                        
 
use EPrints;                                                                                                                                              
 
use strict;                                                                                                                                               
 
# Create new session for interacting with eprints                                                                                                         
my $ep = EPrints->new( cleanup=>0 );
my $session = $ep->repository( 'REPOID');
my $id = 23743;                                                                                                                                           
 
# Create new object referency thing for our desired eprint (23743)                                                                                        
$::pulled_eprint = EPrints::DataObj::EPrint->new( $session, $id );                                                                                        
 
print $::pulled_eprint->get_dataset_id . "\n";                                                                                                            
print $::pulled_eprint->get_type . "\n";                                                                                                                  
 
 
$session->terminate();

This example can be expanded to test work in progress functions as required.

Further reading

Core_API describes many possible activities.