perl自动上网，然后获取网页上的信息：

#!/usr/bin/perl -w
# Perl pragma to restrict unsafe constructs

use strict;

# use LWP::UserAgent model

use LWP::UserAgent;
 
# main function

sub main {

    # get params
    # @_  
    # Within a subroutine the array @_ contains the parameters passed to that subroutine. 
    # Inside a subroutine, @_ is the default array for the array operators push, pop, shift, and unshift.

    my $url = 'http://www.taobao.com';
    die "no url param!\n" unless $url;
 
    # create LWP::UserAgent object

    my $ua = LWP::UserAgent->new;

    # set connect timeout 

    $ua->timeout(20);

    # set User-Agent header

    $ua->agent("Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; SV1; .NET CLR 2.0.50727)");

    # send url use get mothed, and store response at var $resp

    my $resp = $ua->get($url);
 
    # check response

    if ($resp->is_success) {

        # get response content(html source code)

        my $content = $resp->decoded_content;

        # use Regex get page title from $content

        if ( $content =~ m{<title>(.*)</title>}si ) {

            # <title>(.+?)</title> (.+?) match title string, use () to store this str at a special variable $1 (this is a perl variable ),
            # The bracketing construct ( ... ) creates capture groups (also referred to as capture buffers). To refer to the current contents of a group later on, within the same pattern, use $1 for the first,$2 for the second, and so on.

            my $head = $1;
            print "find page title : $head\n";
        } else {
            print "no page title for url : $url\n";
        }
    } else {

#display status information and exit

        die $resp->status_line;
    }
}
 
# pass params to main function,
# @ARGV
# The array @ARGV contains the command-line arguments intended for the script.
 
main(@ARGV);