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Use LWP UserAgent to check and see if a remote site has changed
Standard Web Modules example from a Well House Consultants training course
More on Standard Web Modules [link]

This example is described in the following article(s):
   • Answering ALL the delegate's Perl questions - [link]
   • Automating access to a page obscured behind a holding page - [link]

Source code: cc2 Module: P408
use LWP::UserAgent;

# Get remote site name

$site = $ARGV[0] || "";
$limit = 100;
@omit = ("cgi");

# Keep a local mirror for next time comparison

mkdir $site if (! -e $site) ;

# Grab robots.txt; alert user if it has changed and (manual) check is needed

$agent = LWP::UserAgent->new;
$agent->agent("Well House Consultants");
@alt = ("Not Available","Changed","Unchanged","Freshly Collected");
die "robots.txt was $alt[$altered]\n" if ($altered%2);

# Start at index.html ...

@pagequeue = ("http://$site/index.html");
while ($file = shift @pagequeue) {
        next if ($already{$file}); # Skip pages already checked
        last if (++$npages > $limit); # limit pages to handle
        sleep 5 unless ($npages%10); # Pause to prevent denial of service attack

        $already{$file} = $stat = getpage($file);
        if ($altered == 1 or $altered == 3) {
                print "$file: $stat, page was $alt[$altered]\n";
        # Convert links found so that they can be compared
        foreach (@links) {
                $fully = URI ->new_abs($_,$file) ->canonical;
                $fully =~ s/#.*//;
                $hopper = 1;
                foreach $leave (@omit) {
                        $hopper = 0 if ($fully =~ /$leave/)
                if ($fully =~ m!^http://$site/!i and $hopper) {
                        push @pagequeue,$fully;
$alert and print "alter count is $alert\n";


sub getpage {
$req = HTTP::Request->new(GET => ($pagewant=$_[0]));
$res = $agent->request($req);
$altered = 0; @links = ();
if (($status = $res->code()) == 200) {
        ($mirrorname = $pagewant) =~ tr!/:!%=!;
        $page = $res -> content();
        $altered = 3;
        if (-e "$site/$mirrorname") {
                open (FH,"$site/$mirrorname");
                read (FH, $oldpage, -s "$site/$mirrorname");
                $altered = ($page eq $oldpage) + 1;
        open (FH,">$site/$mirrorname");
        print FH $page;
        @links = ($page =~ m/href\s*=\s*"?([^">\s]+)/ig);
return ($status);
Learn about this subject
This module and example are covered on our public Using Perl on the Web course. If you have a group of three or more trainees who need to learn the subject, we can also arrange a private or on site course for you.

Books covering this topic
Yes. We have over 700 books in our library. Books covering Perl are listed here and when you've selected a relevant book we'll link you on to Amazon to order.

Other Examples
This example comes from our "Standard Web Modules" training module. You'll find a description of the topic and some other closely related examples on the "Standard Web Modules" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
• Our Solutions centre provides a number of longer technical articles.
• Our Opentalk forum archive provides a question and answer centre.
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• And there's a global index here.

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This is a sample program, class demonstration or answer from a training course. It's main purpose is to provide an after-course service to customers who have attended our public private or on site courses, but the examples are made generally available under conditions described below.

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