For that matter, you could just do it like this (adding the suggestion from another reply below):

my %stats;
open(TOP, "top -b -n 1 |");
my $ndone = 0;

while (<TOP>) {
  if ( /up\s.+\s(\d+)\suser.+\s+load\saverage:\s+(\d+\.\d{2}),/ ){
    $stats{users}=$1;
    $stats{load}=$2;
    $ndone +=2;
  }
  elsif ( /(?:Tasks|processes):.+\s+(\d+) running/i ){
    $stats{runproc}=$1;
    $ndone++;
  }
  elsif ( /^Mem:\s+(\d+)k\s+(?:total|av),.+used,\s+(\d+)k\s+free/ ){
    $stats{tmem}=$1;
    $stats{fmem}=$2;
    $ndone += 2;
  }
  last if ( $ndone == 5 );
}
if ( $ndone < 5 ) {
    warn "I only got $ndone factoids from top. Bummer.\n";
}
else {
    print "I got everything in just $. lines of input.\n";
}
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