my @hits = grep defined, m/(?:c(a)|k(t))/g;

##</code><code>##

my @hits;
while ( m/(?:c(a)|k(t))/g ) {
   push @hits, defined $1 ? $1 : $2;
}

##</code><code>##

my @hits;
while ( m/(?:c(a)|k(t)|k(k))/g ) {
   push @hits, defined $1 ? $1
             : defined $2 ? $2
             : $3
}