use strict;
use warnings;

my %seeninfile1;
open FH,"<",$file1 or die "Can't open $file1: $!\n";
while (<FH>) {
  $seeninfile1{$_}++;
}
close(FH);

open FG,"<",$file2 or die "Can't open $file2: $!\n";
while (<FG>) {
  ($key,$number)= split;
  if ($seeninfile1{$key} {
    #do whatever you want to do if key is not in file1
  }
  else {
    #do whatever you want to do if key is in file1
  }
} 
close(FH);