Perl 101 for EPrints

The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.

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.