RRDTool GPRINT formatting with printf

Question

Closely related to this question: Bash printf prefix

I have the following Bash script that is generating an RRDGraph with RRDTool.

#!/bin/bash

now=$(date +%s)
now_formatted=$(date +%s | awk '{printf "%s\n", strftime("%c",$1)}' | sed -e 's/:/\\:/g')

# create power graph for last week
/usr/bin/rrdtool graph /var/www/power-week.png \
--start end-7d --width 543 --height 267 --end $now-1min --slope-mode \
--vertical-label "Watts" --lower-limit 0 \
--alt-autoscale-max \
--title "Power: Last week vs. week before" \
--watermark "(©) $(date +%Y) Alyn R. Tiedtke" \
--font WATERMARK:8 \
DEF:Power=/root/currentcost/ccdata.rrd:Power:AVERAGE \
DEF:Power2=/root/currentcost/ccdata.rrd:Power:AVERAGE:end=$now-7d1min:start=end-7d \
VDEF:Last=Power,LAST \
VDEF:First=Power,FIRST \
VDEF:Min=Power,MINIMUM \
VDEF:Peak=Power,MAXIMUM \
VDEF:Average=Power,AVERAGE \
CDEF:kWh=Power,1000,/,168,* \
CDEF:Cost=kWh,.1029,* \
SHIFT:Power2:604800 \
LINE1:Power2#00CF00FF:"Last Week\\n" \
HRULE:Min#58FAF4:"Min    " \
GPRINT:Power:MIN:"%6.2lf%sW" \
COMMENT:"\\n" \
LINE1:Power#005199FF:"Power  " \
AREA:Power#00519933:"" \
GPRINT:Last:"%6.2lf%sW" \
COMMENT:"\\n" \
HRULE:Average#9595FF:"Average" \
GPRINT:Power:AVERAGE:"%6.2lf%sW" \
COMMENT:"\\n" \
HRULE:Peak#ff0000:"Peak   " \
GPRINT:Power:MAX:"%6.2lf%sW" \
COMMENT:"\\n" \
GPRINT:kWh:AVERAGE:"  total    %6.2lfkWh\\n" \
GPRINT:Cost:AVERAGE:"  cost     %6.2lf £\\n" \
GPRINT:Cost:AVERAGE:"$(printf \\" cost %11s\\" £%.2lf | sed 's/\£/\£ /g')\\n" \
COMMENT:" \\n" \
GPRINT:First:"Showing from %c\\n":strftime \
GPRINT:Last:"          to %c\\n":strftime \
COMMENT:"  Created at $now_formatted"

Which produces a graph like this (notice the leading \ on the lower cost line in the legend):-

Concentrating specifically on the following line:-

GPRINT:Cost:AVERAGE:"$(printf \\" cost %11s\\" £%.2lf | sed 's/\£/\£ /g')\\n" \

This is the line that is printing out the lower cost line in the legend.

I am passing a GPRINT formatted value of £4.54 to Bash's printf function to be padded out to 11 spaces and a cost label prefixed on it. I am then piping this to sed to add a space between the £ and the actual value.

What I want to know is, why is the escaped \ coming through in the output? If I remove the \\ just after printf bash complains that something is missing.

How would I suppress this \ from coming through in the output.

Solution

Try this line:

GPRINT:Cost:AVERAGE:"$(printf ' cost %11s' £%.2lf | sed 's/\£/\£ /g')\\n" \

I changed the inner " marks to ' marks and removed the backslashes.