# Untested and unoptimized code
use strict;
my $filename = 'mlbroster.txt';
my %seen;
open (FILE, $filename) or die "Couldn't open $filename: $!\n";
while (<FILE>) {
  chomp;
  $seen{$_}=1; # This will include, say, $seen{'Sammy Sosa'}
}
close(FILE);
print "Unique players:\n", join("\n", sort keys %seen);