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20.2. Automating Form Submission
20.2.1. Problem
You want
to submit form values to a CGI script from your program. For example,
you want to write a program that searches Amazon and notifies you
when new books with a particular keyword in the title or new books by
a particular author appear.
20.2.2. Solution
If you're submitting form values with GET, use the
get method on an LWP::UserAgent
object:use LWP::Simple;
use URI::URL;
$url = url("http://www.amazon.com/exec/obidos/search-handle-url/index=books");
$url->query_form("field-author" => "Larry Wall"); # more params if needed
$page = get($url);
If you're using
the POST method, create your own user agent and encode the content
appropriately:use LWP::UserAgent;
$ua = LWP::UserAgent->new( );
$resp = $ua->post("www.amazon.com/exec/obidos/search-handle-form",
{ "url" => "index-books",
"field-keywords" => "perl" });
$content = $resp->content;
20.2.3. Discussion
For simple operations, the procedural
interface of the LWP::Simple module is sufficient. For fancier ones,
the LWP::UserAgent module provides a virtual browser object, which
you manipulate using method calls.The format of a query string is:field1=value1&field2=value2&field3=value3
In GET requests, this is encoded in the URL being requested:script.cgi?field1=value1&field2=value2&field3=value3
Fields must still be properly escaped, so setting the
arg form parameter to "this
isn't <EASY> & <FUN>" would yield:http://www.site.com/path/to/
script.cgi?arg=%22this+isn%27t+%3CEASY%3E+%26+%3CFUN%3E%22
The
query_form method called on a URL object correctly
escapes the form values for you, or you could use the
URI::Escape::uri_escape or
CGI::escape_html functions on your own. In POST
requests, the query string is in the body of the HTTP document sent
to the CGI script.You can use the LWP::Simple module to submit data in a GET request,
but there is no corresponding LWP::Simple interface for POST
requests. Instead, the $ua->post method creates
and submits the request in one fell swoop.If you need to go through a proxy, construct your user agent and tell
it to use a proxy this way:$ua->proxy('http' => 'http://proxy.myorg.com:8081');
If a proxy handles multiple protocols, pass an array reference as the
first argument:$ua->proxy(['http', 'ftp'] => 'http://proxy.myorg.com:8081');
That says that HTTP and FTP requests through this user agent should
be routed through the proxy on port 8081 at proxy.myorg.com.
20.2.4. See Also
The documentation for the CPAN modules LWP::Simple, LWP::UserAgent,
HTTP::Request::Common, URI::Escape, and URI::URL; Recipe 20.1; Perl & LWP
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| 20.1. Fetching a URL from a Perl Script |  | 20.3. Extracting URLs |
Copyright © 2003 O'Reilly & Associates. All rights reserved.
