#!/usr/bin/perl
use strict;
use warnings;

my @nme;

# Input loop
while ((print "Enter the name: "), defined (my $input = <STDIN>)) {
    chomp $input;

    last if ! length $input; # Exit loop on empty line
    my ($fn, $ln) = split /\s+/, $input, 2;
    
    if (! defined $fn) {
        print "Blank name ignored\n";
        next;
    }
    
    $ln ||= '_missing_'; # Provide missing name
    print "$fn, $ln\n";
    push @nme, "$ln, $fn";
}   

# Print loop
print "$_\n" foreach sort @nme;