[rrd-users] Help creating graphs using Perl and command line; 'SCALAR' is not a valid function name

A Darren Dunham ddunham at taos.com
Wed May 20 19:16:49 CEST 2009

Brian.Benson reported:
> I'm trying to learn RRDtool using the rrd-beginners web page.  That
> web page shows a shell script and a Perl script that does some of the
> basics.  I have removed almost all the Perl code and got down to the
> call to graph and I'm getting an error:
> "problem generating the graph: 'SCALAR' is not a valid function name"

And in fact the code on the page
<http://oss.oetiker.ch/rrdtool/tut/rrd-beginners.en.html> appears to be
either buggy, or formatted in a way that makes it easy to introduce the
bug for someone trying to copy it.

Perl code at the bottom appears with:

  RRDs::graph ("/images/mem_$count.png",   \
              "--title= Memory Usage",    \
              "--vertical-label=Memory Consumption (MB)", \
              "--start=$start_time",      \
              "--end=$end_time",          \
              "--color=BACK#CCCCCC",      \

Backslashes are common to continue parts of a shell command on another
line, but perl doesn't use them that way.  Instead, these backslashes
are creating references to the item following.  The graph function
doesn't work with the references.


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