my $line = 'This line has a hit here and a hit there.';
my $word = 'hit';

my $count = 0;
my $hilit = '';
while ($line =~ /(.*?)\b($word)\b/sgci) {
   $hilit .= "$1[$2]";
   ++$count;
}
$hilit .= substr($line, pos($line));

print "$hilit\n";
print "$count occurrences of $word\n";