From: Erik Hollensbe <erik@...>
Date: 2008-08-25T22:21:06+09:00
Subject: Re: Open file, get first line, delete first line close file

Rob Biedenharn wrote:
> On Aug 25, 2008, at 4:07 AM, Erik Hollensbe wrote:
> 
>> Dave Bass wrote:
>>> And... it's a lot easier to delete the *last* line of a file than the
>>> first.
>>
>> I don't think this is actually true, can you explain further?
>>
>> -Erik
> 
> 
> You can just truncate the file size.  You don't have any subsequent
> lines (bytes) to move into a new position within the file.

How do you know which line is the last line?

Unless there's something I don't know, that involves reading the whole 
file, or a combination of seek/read from the end until you find the last 
newline, which is essentially what tail +2 does, but starts at the 
beginning of the file.

"Moving" data in a file is the worst possible scenario for I/O at all. 
You can do both of these operations in a single pass read of the file 
without shoving the whole thing into memory at once. It just involves 
writing to one file and reading from another, is all.
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