Having started to follow a few blogs, I needed a reminder of when they change. RSS? I don't know, and I don't know how it works. And web services, like http://www.changedetection.com/, doing this don't check regularly enough.

So I wrote a script, obviously; Dylan - For the sites they are a-changin'

Note 1: It's Windows-biased in the way it starts the web browser when a page changes, but the action can easily be replaced with, say, sending a mail.

Note 2: Why doesn't HEAD work? Why doesn't the headers contain the document's change time? I was under the impression that it should.

#!/usr/local/bin/perl -w
use strict;

use LWP::Simple qw(head get);
use MD5;



print q{Dylan v0.0.1, 2003-03-24, johanl@bossmedia.se
For the sites they are a-changin'

};

main();



sub main {
    my $ext = ".snapshot";
    my $daysLifetime = 14;
    my $secondsDelay = 60 * 10;
    my $commandShow = q{START %s};
    my @aUrl = (
        "http://www.sidhe.org/~dan/blog/",
        );

    while(1) {
        print "\nChecking urls:\n" . join("\n", map { "  $_" } @aUrl) 
+. "\n";
        for my $url( aChangedUrls(\@aUrl, $ext, $daysLifetime) ) {
            my $command = sprintf($commandShow, $url);
            system($command) and warn("Could not show url ($url)\n");
            }

        print "\nZZzzzzz for ($secondsDelay) seconds\n";
        sleep($secondsDelay);
        }
    }



sub aChangedUrls {
    my ($raUrl, $ext, $daysLifetime) = @_;

    my $isFirstTime = ! glob("*$ext");    #No files == first time

    my @aChanged;
    for my $url (@$raUrl) {
        my $text = get($url) or warn("Could not fetch ($url)\n"), next
+;
        my $fileMd5 = MD5->hexhash($text) . $ext;

        if(! -r $fileMd5) {
            open(my $fh, "> $fileMd5") or warn("Could not create ($fil
+eMd5)\n"), next;
            close($fh);

            push(@aChanged, $url);
            }
        }
    @aChanged = () if($isFirstTime);        #It didn't "change" if it 
+was the first time

    #Clean up old stuff
    unlink($_) for ( grep { -M > $daysLifetime} glob("*$ext"));

    return(@aChanged);
    }


__END__
[download]

http://www.bahnhof.se/~johanl/perl/Dylan/dylan.pl.txt