Here are two soluations that does not have a 'seen' print statement in it. Unforuntly both will only stop when you press a second \n or Crtl-C it. This one is the first version I have no special setup required. The problem is that you can easy tell where the monkey is checked.

#!/usr/bin/perl -pal 
if($t++) { exit;  }
$_=join "",("String \'monkey\' was ", (pop @F)!~/monkey/&& 'not ', 'fo
+und in the input string.');
sub BEGIN{ print "Please enter the string to be search for the string 
+'monkey':";}
[download]

This one requires that it be runed with this command
perl -F'monkey' $CODE_FILE
I can't seem to get the -F to work when in the #! of the file. 8(

#!/usr/bin/perl -apn
if ($t++) { exit; }
$_=join "",("String 'monkey' was ", scalar @F ==1 && 'not ', 
        'found in the input string.');
sub BEGIN{ print "Please enter the string to be search for the string 
+'monkey':";}
[download]

--
Pug