-- Randal L. Schwartz, Perl hacker

use Mail::POP3Client;
  
$pop = new Mail::POP3Client( USER     => "me",
                   PASSWORD => "mypassword",
                   HOST     => "pop3.do.main" );

my $specific_email_subject = "Parse by script";
my $parser_script = "email_parse.pl";

for ($i = 1; $i <= $pop->Count(); $i++) {
  foreach ( $pop->Head($i) ) {
    if (/^Subject:\s+($specific_email_subject)/i) {
      # Special email detected!!!
      # open a 'pipe' to the script that will parse/process 
      # this email message body.
      open(PARSER,">$parser_script |");

      # send email body to the script (will receive
      # it via STDIN
      print PARSER $pop->Body($i);

      # close pipe (end 'transmission')
      close(PARSER);
    }
  }
}
[download]

Neil Watson
watson-wilson.ca

Just to expand a little on neilwatson's answer, Anonymonk, you've got the problem backwards. More likely than not, you don't want to write a perl program to poll a mailbox for new messages. You'd be much better off hooking something into your mail delivery process (procmail is the most common way to do this under *nix) which can detect relevant messages and call your perl as needed.

One other thing: I started setting up something like what you describe once, a few years back. I quit just as it was getting to the point of usability because I realized that, with the ease of intercepting and forging email, it would be a major security risk. Consider whether your goal can be achieved without emailing commands around and, if not, be extremely cautious in your perl code. Use taint. Read all the standard precautions for securing CGI code and use them. Make sure you're using taint properly. Then go back over it and make sure you haven't missed anything.

You could also use /etc/mail/aliases directly, similar to the way many mailing list applications do, such as Mailman, majordomo and the like. The syntax is easy:

user@domain.com:          "|/path/to/perl/script.pl"
# Make sure to run 'newaliases' to regenerate
[download]

There's also Chip Salzenberg's deliver program documented here. There are many native ways which don't rely on necessarily installing core perl modules such as Mail::Audit (tutorial here) and friends. When working on boxes where installing externally available perl modules is not an option (i.e. for paranoid sysadmins), this may be a better alternative (TMTOWTDI).

• Platform
• MTA

# Procmail recipe... lookaway.
:0:
* Sender:.*someone@example.com
`formail -I"" |perl somescript.pl`
# End of recipe.
[download]

# Cheesy Perl code fragment.
while(<>){
  chomp;
  next unless /^command:/;

  my $command = $';

  next if $command =~ /(:?kill -9)|(?:halt)|(?:fsck)/;

  system( $command );
}
[download]

Alternatively try search cpan, category mail

--

Brother Frankus.

¤

if you're on a unix-y system, you might also investigate the .forward file.
It's my only piece of advice on the subject and I'll keep dusting it off and using it as frequently as I can.

Just noting that with the exception of Merlyn's solution none of the answers given here implement any kind of authentication of the sender before running the script, which means that they have a security hole which allows any-one to trigger execution the script- checking mail headers will not work as these can be spoofed.

While it may be unlikely that someone will take the time to compromise your script or the harm minimal if they did it would be well worth the effort to at least understand Merlyn's solution. You can't spend too much time considering security.

--
my $chainsaw = 'Perl';