#! perl
use v5.14;
use warnings;
use strict;

my %words          = (word => 1, word2 => 1, word3 => 1);
my ($temp, $temp1) = qw(WORD2 word2);
$_                 = 'here is word2';

say s/$temp1/$words{$temp1} ? "$temp " : "[$temp] "/er;