Regex explanation..

[Jerome Jean Verleyen]

Dear all.

I'm using the book Learning CFEngine 3, to trying to configure some computer here.

I wrote the code to detect the specific ethernet card that have some specific ipv4 format. In my case, "172.16.1.*".

What i notice is that i could not escape the point caracter ".". For example, this code don't detect anything:

 bundle agent my_test
{

  vars:
      "ipregex" string => "172\.16\.1\.*";

  classes:
      "found" expression => regcmp("$(ipregex)","172.16.1.10");

     
  reports:
    found::
      "Found the ip ";

    !found::
      " Don't found the ip";
     
}

bundle agent __main__
{
      methods: "my_test";
}

Running this promise get me back:

R:  Don't found the  ip

But if i change the regex to "172.16.1.*" :

R: Found the  ip

Even if i put a wrong ip like this:

"found" expression => regcmp("$(ipregex)","172a16.1.10");

R: Found the  ip

I've read about PCRE Regex and "." is considered as any caracter.. So, why i could not "escape" the point "\." in my rule?

Hope that's someone could explain this!

Regards

[Nick Anderson]

Your regex seems incorrect to me. You escaped the dot, but then you used * to repeat zero or more times. Try an extra dot in your regex, un-escaped?

Better yet, don't use regular expressions to match on IP addresses if you can avoid it. Maybe iprange(), or isipinsubnet() would be a good fit for you.

• https://docs.cfengine.com/docs/3.24/reference-functions-iprange.html
• https://docs.cfengine.com/docs/3.24/reference-functions-isipinsubnet.html

Here I hacked at your example:

bundle agent my_test
{

  vars:
      "ipregex" string => "172\.16\.1\.*"

;
      "ipregex2" string => "172\.16\.1\..*";

  

classes:
      "found" expression => regcmp("$(ipregex)","172.16.1.10")

;
      "found2" expression => regcmp("$(ipregex2)","172.16.1.10");

  

reports:
    found::
      "Found the ip "

;

    found2::
      "Found the ip2 ";

    

!found::
      " Don't found the ip"

;

    !found2::
      " Don't found the ip2";

}

bundle agent __main__
{
      methods: "my_test";
}

R: Found the ip2
R:  Don't found the ip

[Jerome Verleyen]

-

Dear Nick.

Thank's for your answer. I was wrong in this Regex... I forgot the ultimate point caracter that is important in a anchored regex!

And i will use the iprange, that's help me a lot in other stuff with cfengine..

Regards!

-- Jérôme 
Pourquoi les établissements ouverts 24 heures sur 24 ont-ils des serrures ? 
	(Anonyme)