sub AddToUserArray {
    my ($UserID) = @_; # Like this because it scales well for many params

    # return 1 to skip addtouserlog ()

    # return if bad UserID
    return 1 if $UserID eq "";

    # return if handled user already
    return 1 if grep {$_ eq $UserID} @Participants;

    push @Participants, $UserID;
    return; # Generally better to return undef than 0
}

##</code><code>##

use strict;
use warnings;

my %Participants;

while (<DATA>) {
    chomp;
    
    my ($name, $tail) = split / /, $_, 2;
    
    next if ! defined ($name) || exists $Participants{$name};
    $Participants{$name} = $tail;
    print "Added $name: $tail\n";
}

__DATA__
Fred Red team
Joe Blue Team
Pete Blue Team
Fred Red Team
Annie Red Team
Lee Green Team
Steve Green Team

##</code><code>##

    next if ! defined ($name) || exists $Participants{$name};
    $Participants{$name} = $tail;