#!/usr/bin/perl -w 
 
use strict; 
use MD5; 
use LWP::Simple; 
 
my $url='http://www.mrnick.binary9.net'; 
my $file='sitechanges.txt'; 
 
## grab the contents 
my $content=get($url) || die $!; 
 
## grab the MD5 sum from our datafile 
my $oldmd5=''; 
 
if (-f $file) { 
  open(IN,"<$file") || die $!; 
  $oldmd5=<IN>; 
  close IN; 
} 
 
## generate the new MD5 
my $newmd5=MD5->hexhash($content); 
 
## same? 
if ($newmd5 ne $oldmd5) { 
  ## file has change ... do something 
  ## .... (insert your mailing code here)
  ## then save the new md5 
  open(OUT,">$file") || die $!; 
  print OUT $newmd5; 
  close OUT; 
}
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if ($modified = $string) { print "the file is the same";
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if ($modified eq $string) { print "the file is the same";
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Update: The size of the files you are grabbing IS very important. 18MB is quite bit for casual downloading for comparison. In that case, I would also rely on the headers returned from HEAD (including Content-Length).

If you're dealing with small file then MD5 will be good. The problem is that these files are 12 -18MB each and I have no control on them (someone else is maintaining these files for us). Grabbing 18 MB file from the internet each time sounds like a bad idea to me - doing HTTP HEAD (I call it "giving HEAD" :-)) is more reasonable and faster.

So you're generating an MD5 hash for your file on the URL? how does it work? Ar you automating this somehow? I'm using the header since I need the "last modified" date anyhow.

The MD5 algorithm is described in RFC 1321 and has it's (unofficial) homepage here. RSA Labs currently 'owns' it, FAQ is here.
It's basically a fingerprint algorithm.

For some reason using LWP::Simple's head() doesn't work all that well for me...

Greetz
Beatnik
... Quidquid perl dictum sit, altum viditur.

#!/usr/bin/perl -w

use strict;
use DBI;
use LWP::Simple;
use Digest::MD5  qw(md5 md5_hex md5_base64);

my $dbh = DBI->connect("dbi:mysql:database", "user", "password") || di
+e "Can't connect";

my $sth = $dbh->prepare("select url from sites");
$sth->execute();
my $url = undef;
$sth->bind_col(1,\$url);
my @urls = ();
while($sth->fetch()) { push(@urls, $url); }
$sth->finish();
if (@ARGV) 
{ my $url = $ARGV[0];
  my $page = get($url);
  my ($title) = $page =~ /<TITLE>(.*?)<\/TITLE>/i;
  my $digest = md5_hex($page);
  my $date = time();
  $title =~ s/\'/\\\'/g; 
  my $q = join ("','",$title,$url,$digest,$date);
  $q = "'".$q."'";
  $sth = $dbh->prepare("insert into sites values ('$title','$url','$di
+gest','$date')");
  $sth->execute();
}
$sth->finish();
foreach my $url (@urls) 
{ my $page = get($url);
  print $url,"\n";
  my $digest = md5_hex($page);
  $sth = $dbh->prepare("select checksum from sites where url = '$url'"
+);
  $sth->execute();
  my $checksum = undef;
  $sth->bind_col(1,\$checksum);
  while($sth->fetch)
  { if ($checksum ne $digest)
    { my $date = time();
      my ($title) = $page =~ /<TITLE>(.*?)<\/TITLE>/i;
      my $q = qq|url = "$url", name = "$title", checksum = "$digest", 
+date = "$date"|;
      my $sth2 = $dbh->prepare("update sites set $q where url = '$url'
+");
      $sth2->execute(); 
    }
  }
  $sth->finish();
} 

$dbh->disconnect || die "Disconnection failed";
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if ($modified = $string) { print "the file is the same";
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if ($modified eq $string) {
    print "the file is the same\n";
}
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I have tried both approches (either use 'eq' or just insert the scalar value of the string (array) into both vars and use '==' to compare between them, but the function always returns the "the file is not the same" printout no matter if both strings 'looks' the same. Could it be that there is a space character or CR somewhere in that file that causes to the mismatch?

The string value was in fact surrounded by space characters so it was NOT the same as the other string. I have added some trimming:

for ($modified_scalar) {
        s/^\s+//;
        s/\s+$//;
    }
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and it did the trick!