The 3 lines that you included didn't clarify much for me. If you put <code> ... your text here ... </code> tags around file or program text it will come out verbatim and this makes it a lot easier for us to see what you have.

You say "The file is quite large". If that means its so big that it won't fit into memory, then I would consider using command line grep with the -A and -B options to extract out hunks of stuff that will fit into memory. That should make this "I need stuff before the match" easier. 

from the grep man page....
Context control:
  -B, --before-context=NUM  print NUM lines of leading context
  -A, --after-context=NUM   print NUM lines of trailing context

[download]
Can you show some code of what you have so far? Its really unclear what for example "I need to back up to a known point" means.

In reply to Re: searching across a file then parsing by Marshall
in thread searching across a file then parsing by newperlplayer

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