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Re: Read last expression in a file?

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  • Subject: [mg116163] Re: Read last expression in a file?
  • From: Mark McClure <mcmcclur at>
  • Date: Thu, 3 Feb 2011 05:34:48 -0500 (EST)

On Sat, Jan 29, 2011 at 7:43 PM, Ramiro <ramiro.barrantes at> wrote:

> I wrote a program that generates a lot of Mathematica output.
> Now I need to restart it using the very last expression of such output
> as the new input.   However, I can't find a way to only read the last
> expression in a file, something like a Read that would start at the
> end.

This can be done using Mathematica's low level file manipulation
commands, such as Read and SetStringPosition.  Here's an example.

First, we create a file to play with.

data == RandomInteger[{0, 1}, {100000, 100}];
Export["temp.txt", data];

If you examine the contents of temp.txt, you will find that it is a
30MB file containing one valid Mathematica list per line.  The
following method depends on the file containing one valid expression
per line.

strm == OpenRead["temp.txt"];
p == SetStreamPosition[strm, Infinity];
  Read[strm, Character] ==!== "\n",
  p == SetStreamPosition[strm, p - 1]];
lastLine == Read[strm]

Mark McClure

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