[rrd-users] RRDTOOL Update with script in string

Simon Hobson linux at thehobsons.co.uk
Fri Jan 15 14:50:37 CET 2016

maxmax20 <mak.admin at zoho.com> wrote:

> rrdtool update /home/pi/net/net.rrd N:'cut -d, /home/pi/net/devices.csv -f13
> | cut -d: -f2'::::: to get the first value out of the csv file, but it seems
> that it won't work.

As suggested, put echo in front of it - and possibly pipe the output through hexdump.

One thought, does the SCV file contain exactly one line - not zero lines, not 2 lines (having one line and a newline counts as 2 lines). You may want to add "head -1"

If working in bash, you can cut things down somewhat by using Bash builtin string functions - one some of my data collection scripts, it's made a huge difference. When you use cut you are spawning two new processes (three is you add head as well).

Check the man page for parameter expansion, specifically the ${parameter#word}, ${parameter##word}, ${parameter%word},  and ${parameter%%word} forms. I think this will get you your value :

# Get the file
Utmp=$( < /home/pi/net/devices.csv )

# Get everything after the 12th ','

# Get everything after the first ':'

# Optional - depends on your file, delete everything after the next , or :
Utmp=$(Utmp%%,*) or Utmp=$(Utmp%%:*)

Don't think it applies here (though I don't know if fiddling with IFS might help), but another trick you could try is using arrays. My specific action was getting traffic counts from an interface, so I have a script with :
  Utmp=$(< /proc/net/dev)
I'll leave you to figure it out.

PS - no I didn't come up with this myself, someone else pointed me in that direction.

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