Graphs

martinus.nel at scarceskills.com martinus.nel at scarceskills.com
Tue Oct 26 11:33:05 CEST 2004


Andreas,

I have spent a day or two reading up on regexp, playing with some of the
on-line sites that you can test expressions out on and such.  It's not that
I am completely new to it, it's just that with nagiostat not everything
makes sense to me.

The basics I believe I understand.  There is something else I think I am
missing here.

Let's take the following example:

This is from the nagiostat debug.log file ...

OUTPUT="NTP OK: Offset 0.000312 secs, jitter 0.055 msec, peer is stratum 3"

Now, in my nagiostat.conf I have:

... "output:offset:/-?([0-9.]+)/" "output:jitter:/jitter ([0-9.]+) msec/"

As it is there ^^, this is what happens:

 +VALUE: 0.000492
 +VALUE: 0.157

So far, so fine... Now I change the regexp to read "Offset -?([0-9.]+)", and
still it only pulls the number (a good thing for me, I only want the number
- but that is not how I was understanding things.  The same for the jitter
part, why does nagiostat only pull the numbers ?).
 
But now, ntp offset is not always positive, that is why I added '-?', so, I
get a line that reads:

OUTPUT="NTP OK: Offset -0.000509 secs, jitter 0.157 msec, peer is stratum 3"

And my regexp is ^^, the output:

 +VALUE: 0.000509
 +VALUE: 0.157

What happened to '-' ?  I want to insert a negative value into RRD, so this
is wrong for me.

In that regex coach, I clich on the "split" tab, and what do I see ... it
only picks the numbers.

Is this how nagiostat work, "split" ?
What is "split" ?
and how do I get negative values ?

All help much appreciated :-)

Martinus.
p.s.

Tedman, thank you for that regex-coach :-)


Andreas Ericsson <ae at op5.se> wrote: 
>martinus.nel at scarceskills.com wrote:
>> Michael,
>> 
>> Since you are successful with it, may we lesser beings view some of your
>> templates, especially the regexp ones ? :)
>> 
>> Just in case someone here thinks that I am desperate ... yes I am, I
>just
>> can't seem to get the hang of the regular expressions :-)
>> 
>
>It's really pretty straightforward, so long as you remember a couple of 
>simple rules;
>[abc] denotes a character class and matches any of the characters a, b or
>c.
>* means 'match any or none of the previous character (class)'
>. means 'match any char'.
>There are others as well, but those are the ones that doesn't require 
>odd escaping. Fling around with grep and sed a bit and I'm sure you'll 
>get the idea. For instance, try;
>grep '.*foo.*'
>and then type a lot of gibberish. The lines you type with 'foo' 
>somewhere in them will match and be printed twice.
>
>Regex matching with substitutions works the same way, but it has 
>delimiters at the beginning, the end and between the match and the 
>substitution. The delimiter can be any char, but / and , and # and | are 
>commonly seen in shell-scripts.
>thus
>sed 's/foo/bar/'
>(gibberish goes here)
>will replace (the leading s in the sed command means substitute) foo 
>with bar in any text you type.
>
>Fool around a bit. It's the best way to learn, and you'll learn more as 
>you go along. Should all else fail, pick up a book on perl. It's main 
>feature is just that, regexing, so they're bound to be covered in detail.
>
>-- 
>Andreas Ericsson                   andreas.ericsson at op5.se
>OP5 AB                             www.op5.se
>Lead Developer
>
>
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