A \w matches a single alphanumeric character, not a whole
word.  To match a word you'd need to say \w+.  If use
locale is in effect, the list of alphabetic characters
generated by \w is taken from the current locale.  See the
perllocale manpage. You may use \w, \W, \s, \S, \d, and \D
within character classes (though not as either end of a
range).