Here's a somewhat different approach that works if you only want to anchor at just /^N[aeiou]/.
my %anchors = map { $_ => 1 } qw/ Na Ne Ni No Nu /;
while (my $line = <DATA>) {
my ($number, $item) = split ' ', $line;
my ($first_two) = $item =~ /^(..)/
or die "Word too short: $line";
if (delete $anchors{$first_two}) {
print "Insert '$first_two' anchor here!\n";
}
print $line;
}
__DATA__
1930: Nails <-- #Na here
1939: Navy
1940: Nazi
1941: Nearsighted <-- #Ne here
1942: Neck
1961: Newspaper_Reporter
1963: Nickname <-- #Ni here
1964: Niece
1971: Nipples
1972: Nobility <-- #No here
1973: Noise
1981: November
1982: Nuclear_Bomb <-- #Nu here
1984: Numbers
Result:
Insert 'Na' anchor here!
1930: Nails <-- #Na here
1939: Navy
1940: Nazi
Insert 'Ne' anchor here!
1941: Nearsighted <-- #Ne here
1942: Neck
1961: Newspaper_Reporter
Insert 'Ni' anchor here!
1963: Nickname <-- #Ni here
1964: Niece
1971: Nipples
Insert 'No' anchor here!
1972: Nobility <-- #No here
1973: Noise
1981: November
Insert 'Nu' anchor here!
1982: Nuclear_Bomb <-- #Nu here
1984: Numbers
lodin