Following is fixed code. Should now return data for multiple passed users, and return it in a hash ref, so you can access it by using ${$hash}{users}{username}{cpu}, etc.

Code is a bit cleaned up, but there are many ways I can improve it. Any suggestions are appreciated.

sub userMemCPUpercNidle {
  my @usernames = @_;
  my $topcommand = "top -b -n 1 -u ";
  my $top; # top result
  my $countusers = 0;
  my $rethash;
  
  foreach my $username (@usernames){
    $topcommand .= $username;
    if ($countusers < $#usernames){ # if there are more users
      $topcommand .= ", ";
    }
    $top = `$topcommand`; # gets top from the system
    }
    $top =~ m/(\d+\.\d+)\%id/;    # matches CPU idle time
    $rethash = {'cpuidle' => $1};  # assigns cpu idle to hash
  
  $top =~ s/^.+?Swap[^\n]+\s+//s; # removes everything before the proc
+esses
      
  my @lines = split(/\n/, $top); # split each line into an array value
  my ($cpucol,$memcol,$usrcol);
  
  my $headers = shift(@lines);
  foreach my $col (split(' ', $headers)){ # determines which collumn e
+ach value is in
    if ($col eq 'USER') {
      $usrcol = $colcount; # number of col that is the USER val for pr
+ocess
    } elsif ($col eq '%CPU') {  
      $cpucol = $colcount; # number of col that is the CPU val for pro
+cess
    } elsif ($col eq '%MEM') {  
      $memcol = $colcount; # number of col that is the mem val for pro
+cess
    }

    if (defined($usrcol) && defined($cpucol) && defined($memcol)){
      last;
    } else {
      $colcount++;
    }
  }
  
  foreach my $line (@lines){
    if (defined($cpucol) && defined($memcol) && defined($usrcol)){
      my @values = split(' ', $line);
      ${$rethash}{users}{$values[$usrcol]}{cpu} += $values[$cpucol]; #
+ add process cpu percent to total
      ${$rethash}{users}{$values[$usrcol]}{mem} += $values[$memcol]; #
+ add process memory percent to total
    }
  }
  return $rethash;
}
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