mrras25:

If you really want to step back a few lines, then you can just keep a buffer of the last few lines read. However, I'd suggest just parsing out the elements as you find them, and then insert them when you determine they're "interesting". If you find that it's not an interesting record, clear your list of elements and keep on going. Something like this1: 

my %largerHash;  # Place to accumulate interesting records
my %elements;    # Place to accumulate data into records
while (<INF>) {
    if (/^(yabba|dabba|doo)\s+(.*)/) {
        # We only care about some of the fields
        $elements{$1} = $2;
    }
    elsif (/End of record ID:\s+(.*)/) {
        if ($1 =~ /foo/) {
            # Interesting record (starts with foo) so, store it
            $largerHash{$1} = %elements;
        }
        # Since we found end of record, clear our workspace
        %elements={};
    }
}
__DATA__
Record 1
scooby     7
dooby      8
yabba      Fred
dabba      Wilma
End of record ID: cupcake
Record 2
doo        not fold spindle staple or mutilate
dabba      Barney
yabba      Dino
End of record ID: foobar

[download]

In this example, we collect a couple of fields in record 1, but at the end of the record, we find that nothing was interesting, so we discard the elements we collected. Then we collect more items and at the end of the record, we find that it's interesting, so we add the elements to the larger hash that you want to process after parsing the data.

Note 1: Untested and quite possibly bad syntax, as I've been wrestling a bunch of .Net and C++ code for the last couple of weeks.

...roboticus

Insert witty banter here.

In reply to Re^3: Parsing a Large file with no reason by roboticus
in thread Parsing a Large file with no reason by mrras25

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