title: Unclear errorreport from RRDTool graphing script
body: <p>When one version of a set of scripts runs, which apply RRDTool, you try more of the same .....</p>
  
  <p>Made a version of the lua-script, which now collects power/energy-info, and the related file create_pipower1A_graph.sh is a direct derivative of the errorfree running sh-file described in <a href="https://stackoverflow.com/questions/47139774/rrdtool-how-to-get-png-files-by-means-of-os-execute-call-from-lua-script">RRDTool, How to get png-files by means of os-execute-call from lua-script?</a> </p>
  
  <p>The derivative sh-file should produce a graph with the output of 3 inverters and the parallel consumption.
  That sh-file for graphic output is below.</p>
  
  <pre><code>#!/bin/bash
  rrdtool graph /home/pi/pipower1.png \
    DEF:Pwr_MAC=/home/pi/pipower1.rrd:Power0430:AVERAGE \
    DEF:Pwr_SAJ=/home/pi/pipower1.rrd:Power1530:AVERAGE \
    DEF:Pwr_STECA=/home/pi/pipower1.rrd:Power2950:AVERAGE \
    DEF:Pwr_Cons=/home/pi/pipower1.rrd:Power_Cons:AVERAGE \
    LINE1:Pwr_MAC#ff0000:Output Involar \
    LINE1:Pwr_SAJ#0000ff:Output SAJ1.5 \
    LINE1:Pwr_STECA#5fd00b:Output STECA \
    LINE1:Pwr_Cons#00ffff:Consumption \
    COMMENT:"\t\t\t\t\t\t\l" \
    COMMENT:"\t\t\t\t\t\t\l" \
    GPRINT:Pwr_MAC:LAST:"Output_Involar   Latest\: %2.1lf" \
    GPRINT:Pwr_MAC:MAX:"  Max.\: %2.1lf" \
    GPRINT:Pwr_MAC:MIN:"  Min.\: %2.1lf" \
    COMMENT:"\t\t\t\t\t\t\l" \
    GPRINT:Pwr_SAJ:LAST:"Output SAJ1.5k   Latest\: %2.1lf" \
    GPRINT:Pwr_SAJ:MAX:"  Max.\: %2.1lf" \
    GPRINT:Pwr_SAJ:MIN:"  Min.\: %2.1lf" \
    COMMENT:"\t\t\t\t\t\t\l" \
    GPRINT:Pwr_STECA:LAST:"Output STECA   Latest\: %2.1lf" \
    GPRINT:Pwr_STECA:MAX:"  Max.\: %2.1lf" \
    GPRINT:Pwr_STECA:MIN:"  Min.\: %2.1lf" \
    COMMENT:"\t\t\t\t\t\t\l" \
    GPRINT:Pwr_Cons:LAST:"Consumption    Latest\: %2.1lf" \
    GPRINT:Pwr_Cons:MAX:"  Max.\: %2.1lf" \
    GPRINT:Pwr_Cons:MIN:"  Min.\: %2.1lf" \
    COMMENT:"\t\t\t\t\t\t\l" \
    --width 700 --height 400 \
    --title="Graph B: Power Production &amp; Consumption for last 24 hour" \
    --vertical-label="Power(W)" \
    --watermark "`date`"
  </code></pre>
  
  <p>The lua-script again runs without errors and as result the rrd-file is periodically updated, the graphic output is generated,<strong><em>but</em></strong> no graph appears! Tested on 2 different Raspberries, but no difference in reactions.
  Running the sh-file create_pipower1A_graph from the commandline produces the following errors. </p>
  
  <pre><code>pi@raspberrypi:~$ sudo /home/pi/create_pipower1A_graph.sh
  ERROR: 'I' is not a valid function name
  pi@raspberrypi:~$ ./create_pipower1A_graph.sh
  ERROR: 'I' is not a valid function name
  </code></pre>
  
  <p><strong>Question:</strong> Puzzled, because nowhere in the sh-file an I is applied as function command. Explanation? Hint for remedy of this error?</p>