#!/usr/bin/perl -w
use strict;

my %unique_values;

#open file two first and read in the values of interest
unless(open(F2, "file2name.txt")){
    die "a horrible death!";
}else{
    #line by line split off the first word i.e. user01, user02, etc
    %unique_values = map{ (split / /,$_)[0], undef }<F2>;
    close F2;
    unless(open(F1, "file1name.txt")){
        die "a horrible death!";
    }else{
        while(<F1>){
            chomp;
            if(exists($unique_values{$_}){
                delete $unique_values{$_});
            }
        }
        close F1;
    }
}
#open a file for output
unless(open(OUT, ">outputfile.txt")){
    die "again we fail!";
}else{
    print $_."\n" for(sort keys %unique_values);
    close OUT;
}