[rrd-users] Concatenated VDEF and CDEF commands in a rrdtool graph cmd

[Tobias Oetiker]

Today Steve Shipway wrote:

> Have you tried this:
>
> CDEF:dtmaxdiff=dt,POP,dtfoo,16,-
>
> This uses a DEF variable (dt) although it is removed by the POP
> to trick the CDEF into having at least one dataset variable (dt)
> to base the new sequence off of.  I'm still not sure if RRDTool
> lets you use the VDEF value as a constant, though... I suspect
> not but havent tried it in the latest version of RRDTool

this will work
tobi

>
> Steve
> Steve Shipway
> University of Auckland ITS
> UNIX Systems Design Lead
> s.shipway at auckland.ac.nz<mailto:s.shipway at auckland.ac.nz>
> Ph: +64 9 373 7599 ext 86487
>
> ________________________________
> From: rrd-users-bounces+s.shipway=auckland.ac.nz at lists.oetiker.ch [rrd-users-bounces+s.shipway=auckland.ac.nz at lists.oetiker.ch] on behalf of Rob Newman [rlnewman at ucsd.edu]
> Sent: Thursday, 11 November 2010 2:03 p.m.
> To: rrd-users at lists.oetiker.ch
> Subject: [rrd-users] Concatenated VDEF and CDEF commands in a rrdtool graph cmd
>
> Hi there,
>
> Does anyone know why this fails:
>
> rrdtool graph /path/to/outputimage/rrd.png \
>     --interlaced --imgformat PNG --end 1289434618 --start 1286756217 \
>     --width 600 --height 200 --title 'TEST' \
>     DEF:dt=/path/to/dt.rrd:dt:AVERAGE \
>     VDEF:dtfoo=dt,MAXIMUM \
>     CDEF:dtmaxdiff=dtfoo,16,- \
>     LINE1:dtmaxdiff#990000:'TESTFOO' \
>     GPRINT:dt:LAST:'Latest value for TESTFOO\: %4.0lf%s\j'
>
> The output I get from rrdtool is:
>
> ERROR: rpn expressions without DEF or CDEF variables are not supported
>
> If I try and add backslashes to the path (a la http://www.mrtg.org/rrdtool/doc/rrdgraph_rpn.en.html, note between the VDEF and CDEF rpn command there is not a carriage return anymore, just whitespace and a backslash):
>
> rrdtool graph /path/to/outputimage/rrd.png \
>     --interlaced --imgformat PNG --end 1289434618 --start 1286756217 \
>     --width 600 --height 200 --title 'TEST' \
>     DEF:dt=/path/to/dt.rrd:dt:AVERAGE \
>     VDEF:dtfoo=dt,MAXIMUM \ CDEF:dtmaxdiff=dtfoo,16,- \
>     LINE1:dtmaxdiff#990000:'TESTFOO' \
>     GPRINT:dt:LAST:'Latest value for TESTFOO\: %4.0lf%s\j'
>
> I now get the output:
>
> ERROR: Could not make sense out of ' CDEF:dtmaxdiff=dtfoo,16,-'
>
> What I want is to find the maximum value for the data set ('dtfoo = dt,MAXIMUM'), then take that value and subtract 16 from it (dtmaxdiff = dtfoo,16,-), then plot that value.
>
> Any ideas why both of these fail?
>
> Thanks in advance,
> - Rob
>

-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900