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Re: Parsing a Large file with no reason

by mrras25 (Acolyte)
on Jan 28, 2010 at 23:23 UTC ( #820270=note: print w/ replies, xml ) Need Help??


in reply to Parsing a Large file with no reason

I was just trying to have people to bounce some ideas off of - however this is what I came up with - its crude and runs slow on large files (the 1 file I am running this off of as a test is 80,000+ lines long) - If someone sees something I can do differently I am open to suggestions

#!/usr/bin/perl use strict; use warnings; no warnings 'uninitialized'; use Data::Dumper; use Tie::File; my $base = $ARGV[0]; open(FILE, $base) || die "Unable to locate file: $!\n"; my (@searray,@flarray); tie(@flarray, 'Tie::File',$base); while(<FILE>) { my ($start,$end); chomp; if($_ =~ /-El\s+vg/../vgserial_id/) { $start = (split /\s+/,$_)[3] if($_ =~/-El/); $end = (split /\s+/, $_)[1] if($_ =~/vgserial_id/); } if(defined $start) { push(@searray, $start); } else { $start = ''; +} if(defined $end) { push(@searray, $end); } else { $end = ''; } } my %hash_ref = @searray; #print Dumper \%hash_ref; foreach my $hkey(keys %hash_ref) { my $hvalue = $hash_ref{$hkey}; my $count = 0; for (my $i = 0; $i < @flarray; $i++) { next unless $flarray[$i] =~ /$hvalue/; next if($flarray[$i] =~ /vgserial_id/); my ($mc,$lvsip) = (($i-1),($i-5)); my $mount = (split /\s+/, $flarray[$mc])[1]; my $lvnam = (split /\s+/, $flarray[$lvsip])[3]; next if($mount =~ /None/); print "$i: VG: $hkey : MOUNT: $mount : LV_name: $lvnam : SIZE: $ +size\n"; } }


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Re^2: Parsing a Large file with no reason
by Cristoforo (Deacon) on Jan 29, 2010 at 02:25 UTC
    It is so slow on large files because for each matching record, you loop through all 80,000 lines; So, if you had had 4000 matching records, you would have 4000 * 80000 = 320,000,000 iterations. There must be a better method I think.

    And I don't know if you can 'tie' the same file (as an array) while opening it for reading (both at the same time).

    Note that I set the input record separator, $/, to ---- lsattr , (with a space following lsattr), to read a record at a time.

    Not seeing more sample data, I made a guess at what might work and it did work with your sample data. But again, it's difficult to tell.

    #!/usr/bin/perl use strict; use warnings; use Data::Dumper; my $base = $ARGV[0] or die "Must supply a filename to open. $!"; open my $fh, "<", $base or die "Unable to locate file: $!\n"; my %data; { local $/ = "---- lsattr "; while (<$fh>) { chomp; next unless /^-El\s+(\S+)/; my $vg = $1; next unless /^label\s+(\S+)/m; my $label = $1; next if $label eq "None"; next unless /^lvserial_id\s+(\S+)/m; my $name = $1; next unless /^size\s+(\d+)/m; my $size = $1; @{ $data{ $vg } }{ qw/ label name size / } = ($label, $name, $ +size); #print "VG: $vg : MOUNT: $label : LV_name: $name : SIZE: $size +\n"; } } print Dumper \%data;
    Update: The data structure created above will only work if there is only 1 record for each sought key, ($vg). If there is more than 1 record with the same key, the data structure will only contain the last fields parsed from the file. It will silently give you incorrect results.

    That said, I would need to know more about your file to be able to suggest a suitable data structure.

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