Perl in a Nutshell, 2nd Edition

LWP Overview

Any web transaction requires an application that can establish a TCP/IP network connection and send and receive messages using the appropriate protocol (usually HTTP). TCP/IP connections are established using sockets, and messages are exchanged via socket filehandles. (See Chapter 15 for information on how to manually create socket applications.) LWP provides an object for this application with LWP:: UserAgent for clients; HTTP::Daemon provides a server object. The UserAgent object acts as the browser: it connects to a server, sends requests, receives responses, and manages the received data. This is how you create a UserAgent object:

use LWP::UserAgent;
$ua = LWP::UserAgent->new(  );

The UserAgent now needs to send a message to a server requesting a Universal Resource Locator (URL) using the request method. request forms an HTTP request from the object given as its argument. This request object is created by HTTP::Request .

An HTTP request message contains three elements. The first line of a message always contains an HTTP command called a method; a Universal Resource Identifier (URI), which identifies the file or resource the client is querying; and the HTTP version number. The following lines of a client request contain header information, which provides information about the client and any data it is sending the server. The third part of a client request is the entity body, which is data sent to the server (for the POST method). The following is a sample HTTP request: ...