(wrt to use strict ) Um, okay, but then this is bad:

    foreach $word ( @wordlist ) {
        ....
    }
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From this, it clearly looks like $word should be a lexical variable only visible in the foreach block.

And yeah, I didn't realize there was a print statement in the foreach loop ( I was printing out something completely irrelevant ). I see the problem: you're using @wordlist for both the foreach loop and the grep. Of course grep will return an non-empty array, silly ;-)

Update

use strict;
my @nocapslist = qw/ 
    in and the for it but to with about or nor because as that
/;  
    
sub make_a_title {
    my $string = shift;
    $string =~ s/^\s+//;
    my @wordlist = split (/\s+/, ucfirst( $string ) );

    join( ' ',
        map{
            my $word = $_;
            ## not quite efficient like Ovid's;-)
            (grep{ $_ eq $word } @nocapslist) ? $word : ucfirst( $word
+ );
        } @wordlist
    );
}

my $str = "this is a sentence, for You and For me  Blah Blah blah";
print make_a_title( $str );
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