Sure you can. If your data is nice and normal like in the first example you can do something like this.

@sentence = split /\s/,"perlmonk perlmonk perlmonk "; 
$numWords = @sentence;
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to count the number of occurrences of perlmonk and not other words you could use the same idea but with a regular expression. I will leave it to you to figure it out. This is a clunky way to do it....

@sentence = split /\s/,"perlmonk perlmonk perlmonk  and some other wor
+ds that are not perlmonk"; 
foreach $word (@sentence) { 
   if ( $word =~/perlmonk/) {
      $numOccur++;
   }
}
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The last one would be more tricky, but it can be done with a fairly easy regxp... something along the lines of  /p\s*e\s*..... should do the trick
Good luck.
Disclamer: all code untested and off the top of my head.