# test string
my $link_results = '<p>Hello: World Hello hello drewboy Drewboy: Drewboy!</p>';

# define an array of the terms we want to bold
my @terms = ( 'Hello:', 'Drewboy!' );

# make all the terms regex safe by quotemeta-ing them
$_ = quotemeta $_ for @terms;

# join all terms with a pipe | so we find any of them - alternation
my $bold = join '|', @terms;

# make all the subs - case sensitive and global
$link_results =~ s#(<[^>]+?>)|($bold)#$1 ? $1 : "<b>$2</b>"#eg;

# proof is in da pudding
print $link_results;