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5.2. LWP and GET Requests

The way you submit form data with LWP depends on whether the form's action is GET or POST. If it's a GET form, you construct a URL with encoded form data (possibly using the $url->query_form( ) method) and call $browser->get( ). If it's a POST form, you call to call $browser->post( ) and pass a reference to an array of form parameters. We cover POST later in this chapter.

5.2.2. GETting a query_form( ) URL

The tidiest way to submit GET form data is to make a new URI object, then add in the form pairs using the query_form method, before performing a $browser->get($url) request:

$url->query_form(name => value, name => value, ...);

For example:

use URI;
my $url = URI->new( 'http://www.census.gov/cgi-bin/gazetteer' );
my($city,$state,$zip) = ("Some City","Some State","Some Zip");
$url->query_form(
  # All form pairs:
  'city'  => $city,
  'state' => $state,
  'zip'   => $zip,
);

print $url, "\n"; # so we can see it

Prints:

http://www.census.gov/cgi-bin/gazetteer?city=Some+City&state=Some+State&zip=Some+Zip

From this, it's easy to write a small program (shown in Example 5-1) to perform a request on this URL and use some simple regexps to extract the data from the HTML.

Example 5-1. gazetteer.pl

#!/usr/bin/perl -w
# gazetteer.pl - query the US Cenus Gazetteer database

use strict;
use URI;
use LWP::UserAgent;

die "Usage: $0 \"That Town\"\n" unless @ARGV == 1;
my $name = $ARGV[0];
my $url = URI->new('http://www.census.gov/cgi-bin/gazetteer');
$url->query_form( 'city' => $name, 'state' => '', 'zip' => '');
print $url, "\n";

my $response = LWP::UserAgent->new->get( $url );
die "Error: ", $response->status_line unless $response->is_success;
extract_and_sort($response->content);

sub extract_and_sort {  # A simple data extractor routine
  die "No <ul>...</ul> in content" unless $_[0] =~ m{<ul>(.*?)</ul>}s;
  my @pop_and_town;
  foreach my $entry (split /<li>/, $1) {
    next unless $entry =~ m{^<strong>(.*?)</strong>(.*?)<br>}s;
    my $town = "$1 $2";
    next unless $entry =~ m{^Population \(.*?\): (\d+)<br>}m;
    push @pop_and_town, sprintf "%10s %s\n", $1, $town;
  }
  print reverse sort @pop_and_town;
}

Then run it from a prompt:

% perl gazetteer.pl Dulce
http://www.census.gov/cgi-bin/gazetteer?city=Dulce&state=&zip=
      2438 Dulce, NM  (cdp)
       794 Agua Dulce, TX  (city)
       136 Guayabo Dulce Barrio, PR  (county subdivision)
 
% perl gazetteer.pl IEG
http://www.census.gov/cgi-bin/gazetteer?city=IEG&state=&zip=
   2498016 San Diego County, CA  (county)
   1886748 San Diego Division, CA  (county subdivision)
   1110549 San Diego, CA  (city)
     67229 Boca Ciega Division, FL  (county subdivision)
      6977 Rancho San Diego, CA  (cdp)
      6874 San Diego Country Estates, CA  (cdp)
      5018 San Diego Division, TX  (county subdivision)
      4983 San Diego, TX  (city)
      1110 Diego Herna]Ndez Barrio, PR  (county subdivision)
       912 Riegelsville, PA  (county subdivision)
       912 Riegelsville, PA  (borough)
       298 New Riegel, OH  (village)


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