How does Cron affect the Getopt::Long module?

I've written a wrapper program 开发者_Python百科for mailx using perl that allows me to easily add attachments and do some other nifty things that were a little frustrating to accomplish with mailx.

In the first few lines I have:

use strict;
use warnings;
use Getopt::Long;

my ( $to, $from, $subject, $attachments, $body, $file ) = (undef) x 7;

GetOptions(
    "to=s"          => \$to,
    "from=s"        => \$from,
    "subject=s"     => \$subject,
    "attachments=s" => \$attachments,
    "body=s"        => \$body,
    "file=s"        => \$file,
);
$to      = getlogin unless $to;
$from    = getlogin unless $from;
$subject = " "      unless $subject;

This wrapper up until now has worked fine when being called by other scripts. However now that we have a script being run by the Cron some funny things are happening. This Cron job calls the wrapper by only specifying -t and -su but omitting -fr (yes abbreviations of the flags are being used). The resulting email correctly sets the To: however has the Sender listed as -s@blah.com with the subject line blank. As per the above code I can only assume that there is something strange going between Cron and the Getopt::Long module. Does anyone know why a Cron job may cause this odd behavior? If it is something else that is wrong what would it be?

Perl's getlogin probably doesn't return anything useful from cron, quoting from getlogin(3):

   getlogin() returns a pointer to a string containing
   the name of the user logged in on the controlling
   terminal of the process, or a null pointer if this
   information cannot be determined.

I suggest changing your crontab to always include the username explicitly for any options that rely on getlogin. You could also change your wrapper to use getpwuid($<). (See perlvar(1) and perlfunc(1) for details on $< and getpwuid.)

Why that screws up your mailx, I don't know, but I'm going to guess you're using backticks, exec or system with a string to start mailx, rather than exec or system with a list.