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From: sfeam <sfeam@users.sourceforge.net>
Newsgroups: comp.graphics.apps.gnuplot
Subject: Re: How to know total number of blocks in a file?
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Date: Thu, 15 Mar 2012 09:53:04 -0700
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ampbox@gmail.com wrote:

> Hi all,
> 
> I have a data file with multiple data blocks (groups of data lines
> separated by blank lines). I want to plot only the last block.
> 
> I can do it like
> 
>       plot 'filename' every :::<blockNO>::<blockNO>
> 
> where <blockNO> is the block number, and since it is the last block,
> this number equals the total number of blocks in my data file.
> 
> The problem is, I don't know how many blocks are there in my data
> file. (Because my simulation adds a new block every few hours and the
> longer simulation runs, the more number of frames (block) I get.)
> 
> Is there a built-in variable like GPVAL_DATA_X_MAX etc. to give me
> this information?

Not currently.  There is a contributed patch on the SourceForge 
tracker that claims to add something like this (I haven't looked at it
so I don't know the details). 

> Another possible solution: can I get the number of lines etc. by a
> bash command (I am in Linux) INSIDE my gnuplot script and give it to a
> variable? I mean something like:
> 
> NBLOCKS = `!wc -l filename`

Sure. 
But wc unfortunately returns a line that contains also the filename. 
So you need:

  WC = `wc -l filename`
  NBLOCKS = word(WC,1)


> 
> Thanks in advance,
> Masoud.