Dear Perl Monks, I am developing at the moment a script which has to parse 20GB files. The files I have to parse are some logfiles. My problem is that it takes ages to parse the files. I am doing something like this: 

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>;
      }
   }
}

[download]
I've already tried to speed it up by using the regExp flag=>o by doing something like this: 

$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;
}

[download]
I don't know how to optimize this more. Maybe it would be possible to do something with "map"? I think the "o" flag didn't speed it up at all. Also I've tried to split the one big file into a few small ones and use some forks childs to parse each of the small ones. Also this didn't help. Thanks a lot for your help! -Marco

In reply to how to parse large files by domcyrus

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