Thanks for that reminder. :-) After thinking about what you wrote, I did a "which ?1" as choroba indicated, and it found a file called z1, which contained the phrase "hello world". The question remains why the hex control characters remained in the shell. I believe roboticus is right about this, that the terminal's answerback setting got set by the Perl script, and it printed out z1 in binary or hex. Strange, but I understand now.