Note that if all you want to do is collect up the service name related to a port, Perl's got getservbyport:

use warnings;
use strict;

my @ports = qw(21 22 23);
my $protocol = 'tcp';

for (@ports){
    my ($name, $alias, $num, $proto) = getservbyport($_, $protocol);
    print "$num: $name\n";
}
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