open my $file_handle, $mode, $filename or die $!;

##</code><code>##

#!perl

use strict;
use warnings;

my %seen;

while (my $line = <DATA>) {
    my ($key, $rest) = split /,/, $line, 2;
    $key =~ s{ [-&_+'] }{ }msx;
    $key =~ s{ ( [a-z] ) ( [A-Z] ) }{$1 $2}msx;
    
    if ($seen{$key}++) {
        print STDERR join '', 'DUP: ', $line;
    }
    else {
        print STDOUT join '', 'NEW: ', $key, ',', $rest;
    }
}

__DATA__
Group One,Captain,Phone Number,League Pos,etc.
Group-One,Captain,Phone Number,League Pos,etc.
GroupOne,Captain,Phone Number,League Pos,etc.
Group Two,Captain,Phone Number,League Pos,etc.
Group Three,Captain,Phone Number,League Pos,etc.

##</code><code>##

$ del_dup_prob.pl
NEW: Group One,Captain,Phone Number,League Pos,etc.
DUP: Group-One,Captain,Phone Number,League Pos,etc.
DUP: GroupOne,Captain,Phone Number,League Pos,etc.
NEW: Group Two,Captain,Phone Number,League Pos,etc.
NEW: Group Three,Captain,Phone Number,League Pos,etc.

##</code><code>##

$ del_dup_prob.pl
NEW: Group One,Captain,Phone Number,League Pos,etc.
DUP: Group-One,Captain,Phone Number,League Pos,etc.
NEW: GroupOne,Captain,Phone Number,League Pos,etc.
NEW: Group Two,Captain,Phone Number,League Pos,etc.
NEW: Group Three,Captain,Phone Number,League Pos,etc.

##</code><code>##

script_name input_filename > unique_rows_filename 2> duplicate_rows_filename