How about something like this

sub count {
        # pass it the long sentence and the match word/char!
    my ($LONG,$CHAR) = @_;
    my $count = 0;
    while ($LONG=~m/$CHAR/) {
        $LONG=~s/$CHAR//; # remove match?
        $count++;
    }
    return $count;
}
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Then you can call it in your code like this

foreach ( @check ) {            
        print "[$_]: " . count($string,$_);
       }
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Well, it looks a bit messy, but it does exactly what you need with high performance.