cross walk example script (HHS#14)

* Updated README to include information on OS X certificate requirements

* Crosswalk example

* Small changes to crosswalk.pl

I hope you don't mind - I changed your 't' argument to 'i' for identifier rather than 'term'.   I tested to make sure it works.
Thanks for this contribution.

Author: spiros

samples/perl/crosswalk.pl

@@ -0,0 +1,69 @@
+#!/usr/bin/perl -w
+
+## usage: perl crosswalk.pl -u your-umls-username -p your-umls-password -v source vocabulary -i source vocabulary identifier [ -r specify target vocabulary]
+## Performs a crosswalk using the latest UMLS version and retrieves all codes that share a UMLS CUI with a particular code.
+## Example: 
+## perl crosswalk.pl -u username -p password -v HPO -i HP:0001947
+## perl crosswalk.pl -u username -p password -v HPO -i HP:0001947 -r SNOMEDCT_US
+## More information: https://documentation.uts.nlm.nih.gov/rest/source-asserted-identifiers/crosswalk/index.html
+
+use lib "lib";
+use strict;
+use URI;
+use Authentication::TicketClient;
+use JSON;
+use REST::Client;
+use Data::Dumper;
+use Getopt::Std;
+
+## parse command line arguments
+our ($opt_u,$opt_p,$opt_v,$opt_i, $opt_r);
+getopt('upvir');
+my $username = $opt_u || die "please provide username";
+my $password = $opt_p || die "please provide password";
+my $source   = $opt_v || die "Please provide a source vocabulary";
+my $identifier = $opt_i || die "Please provide a source vocabulary identifier";
+
+## Create a ticket granting ticket for the session
+my $ticketClient = 
+  new TicketClient(username=>$opt_u,password=>$opt_p,service=>"http://umlsks.nlm.nih.gov",tgt=>"") || die "could not create TicketClient() object";
+my $tgt = $ticketClient->getTgt();
+my $uri = new URI("https://uts-ws.nlm.nih.gov");
+my $json;
+my $client = REST::Client->new();
+my %parameters = ();
+
+my $path = sprintf("/rest/crosswalk/current/source/%s/%s", $opt_v, $opt_i);
+
+if ( defined $opt_r && $opt_r ){
+  $parameters{'targetSource'} = $opt_r
+}
+
+## Query the API
+$json = run_query($path,\%parameters);
+my $ra_results = $json->{'result'};
+
+## Loop through results
+foreach my $result( @$ra_results ) {
+  printf("%s %s %s\n", $result->{'rootSource'}, $result->{'ui'}, $result->{'name'} )
+}
+
+
+sub format_json {
+  my $json_in = shift;
+  my $json    = JSON->new;
+  my $obj     = $json->decode($json_in);
+  return $obj;
+}
+
+sub run_query {
+  my ($path, $parameters) = @_; 
+  $parameters{ticket} = $ticketClient->getServiceTicket();
+  $uri->path($path);
+  $uri->query_form($parameters);
+  print qq{$uri\n\n};
+  my $query = $client->GET($uri) || die "Could not execute query $!\n";
+  my $results = $query->responseCode() eq '200'? $query->responseContent: die "Could not execute query $!\n";
+  my $json = format_json($results);
+  return $json;
+}