Doesn't mailx need some input on it's STDIN, like the message for instance? I think you need to do something like (untested) :

  open MAILX,'|/bin/mailx -s "hello" john@work.com' or die $!;
  print MAILX 'Your message here';
  close MAILX or die "mailx: $! $?";
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I would however recommend using another mechanism to send mail in your program, not limited to piping directly to sendmail or using a module such as Email::Send

/J\