If you print out this:

substr ($string, 0, length $keyword)
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you'll see that it's "The fred array gets a".

It equates to "characters zero to 20 of $string"..

So what you asked Perl to do is tell you if your keyword contained those 20 characters.

So, yes, you were obviously a little confused.
--

“Every bit of code is either naturally related to the problem at hand, or else it's an accidental side effect of the fact that you happened to solve the problem using a digital computer.”
M-J D