Description: |
This code fragment was written with the intent to minimise some of my system administration overhead by providing a script framework that allowed arbitrary scripting actions to be performed should a web page be modified or updated. The code uses LWP::UserAgent to get a web page and then should the web page have changed since the last execution of the script, as measured by the last_modified header or should this be unavailable, an MD5 digest of the page contents, execute a script subroutine or method.
Independent subroutines can be specified for different URLs, in the single example provided, the subroutine virus_alert is executed should the Symantec web page have changed since the last execution of the script. |
#!/usr/bin/perl -Tw
use Carp;
use DB_File;
use Digest::MD5 qw/md5_hex/;
use Fcntl qw/:flock/;
use HTTP::Request;
use LWP::UserAgent;
use URI;
use strict;
# %despatch_table hash
#
# The keys of this hash specify the web page to monitor,
# with the corresponding hash values containing references
# to the script method or subroutine to be executed upon
# change in the web page.
#
my %despatch_table = (
'http://securityresponse.symantec.com/avcenter/vinfodb.html' =>
+ 'virus_alert'
);
# Create a DBM hash containing the last modification time
# or page MD5 hash, indexed by the page URL
my %index;
my $db = tie %index, 'DB_File', "wpmon.dbm", O_CREAT | O_RDWR, 0666;
my $fd = $db->fd();
open (DF, "+<&=$fd") || croak $!;
flock (DF, LOCK_EX) || croak $!;
# Add any new keys within %despatch_table to the array
# of URLs to monitor
my @urls = keys %index;
foreach my $url (keys %despatch_table) {
push (@urls, $url) unless (exists $index{$url});
}
my $ua = LWP::UserAgent->new;
foreach my $url (sort @urls) {
my $uri = URI->new($url);
my $request = HTTP::Request->new('GET', $uri->canonical->as_string
+);
my $response = $ua->request($request);
if ($response->is_success) {
# Update measure for page is last_modified header if
# defined or failing this, an MD5 digest of the page
my $html = $response->content;
my $unique = $response->last_modified || md5_hex($html);
$index{$url} = $unique unless (exists $index{$url});
if ($index{$url} ne $unique) {
# Ensure that a code or method reference still exists
# within the %despatch_table hash - If so, execute it
# via an eval statement
if (exists $despatch_table{$url}) {
$html = quotemeta $html;
eval qq/
$despatch_table{$url}("$html")
/;
carp $@ if $@;
}
$index{$url} = $unique;
}
}
}
undef $db;
untie %index;
close DF;
exit 0;
sub virus_alert {
# ... response code to changed web page within subroutines
}
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