[rrd-users] Help with: Input from a file in the RRD Graph

[Simon Hobson]

Mats Gustavsson <wwwmazzse at gmail.com> wrote:

> I have a Perl script that creates a .png file with the graph. So far so good.
> In the Graph I have the function "HRULE:22#000000" that works just fine.
> 
> Now I want to make the value 22 flexible. I want it be be read from a external file.
> So when I just change the value to 21, or 23 or what ever, its been read from a file.
> 
> Because the value in the file ex 22 is being read from multiple scripts, both a bash and a python script, I want it to pick the value from the file to the HRULE in the RRDs::Graph, in the perl Script.
> 
> The file, that is today being read from bash and python, is just containing a value between -30 to +50. So the help that I need with, it needs to handle a value ex -5 and 22.
> 
> The reason I want it to read from the same file, is that I just needs to adjust in two files.
> File 1 High value like -5
> File 2 Low value like 22.
> Instead in 20-24 different places, that is easily to miss a place to change.
> 
> I hope that some one can help me.

TBH I'm not sure what the question is ! It seems that you've already figured out that the way to do this is to put the values into files, and read those files in to set a variable that you can then use in building the RRD command. In bash I'd be thinking along the lines of :

MaxLineValFile="/some/path/to/file"
read $MaxlineVal < ${MaxLineValFile}
# Apply some sanity checking here !
rrdtool ... ${MaxLineVal} ...

I actually use rrdcgi in my scripts (cgi scripts served up by Apache), like this :

(
  echo some stuff
  echo more stuff
  some conditional stuff
  ...
) | /usr/bin/rrdcgi --filter - 2>&1 > /dev/null

This is because some of my RRD stuff is quite large - biggest is 254 values stacked, plus another 254 valued inverted and stacked, plus a legend for min and average for each. I did try building up the list of RRD commands in a text variable and then calling "rrdtool graph ${command_list}" but it got really slow building that up.