my %lookingFor; 
# keys => different name of one subset
# values => array of one subset
my $fh = new FileHandle "< largeLogFile.log";

while (<$fh>) {
  foreach my $subset (keys %lookingFor) {
    foreach my $item (@{$subset}) {
      if (<$fh> =~ m/$item/) {
        my $writeFh = new FileHandle ">> myout.log";
        print $writeFh <$fh>;
      }
   }
}

##</code><code>##


$isSubSet=buildRegexp(@allSubSets);

while (<$fh>) {
  foreach my $subset (keys %lookingFor) {
      if (&$isSubSet(<$fh>)) {
        my $writeFh = new FileHandle ">> myout.log";
        print $writeFh <$fh>;
      }
   }
}

sub buildRegexp {
  my @R = @_;
  my $expr = join '||', map { "\$_[0] =~ m/\(To\|is\)\\:\\S\+\\@\$R[$_]/io" } ( 0..$#R );
   my $matchsub = eval "sub { $expr }";
   if ($@) {
     $logger->error("Failed in building regex @R: $@");
     return ERROR;
        }
     $matchsub;
}