A regular expression is all what you need, take a look at perlre. Just to give you an example see if the following code does what you want:

my $text = 'whatever you want in here';
my $n = 10;
my $word = 'match';
if ( $text=~ /(([.\s]+\w+){$n}[.\s]+$word[.\s]+(\w+[.\s]+){$n})/ )  {
    print $1;
}
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