string data expressions (was Re: using option 82 to assign a static ip-address)

[Glenn Satchell]

On Tue, December 18, 2012 1:28 am, perl-list wrote:
> Glenn,
>
> Don't mean to hijack the thread but...
>
> Is that right? I did not know that if you simply do not enclose the match
> text in quotes that it would match binary info!! That de-screws something
> that I have been struggling with! Some option 82 from some manufacturers
> is binary, others it is ASCII. If I simply can match in this manner ...
>
> Does this work for ASCII as well or only binary?
>
> hmmm - what to do if the text that the manufacturer sends is something
> like: VLAN 1 Port 4
>
>> These can all be re-written without the binary-to-ascii and be much
>> clearer:
>
>> match if substring(option agent.remote-id, 2, 7)) = 84:78:ac:84:e5:80
>> and hardware = 1:0:14:2d:40:f:15
>> and substring(option agent.circuit-id, 5, 1)) = e;

You can use a colon list of hexadecimal characters to represent a string.
This is from the dhcp-eval man page:

     string

       A string, enclosed in quotes, may be specified as  a  data
       expression,  and  returns  the  text  between  the quotes,
       encoded in  ASCII.    The  backslash  ('\')  character  is
       treated  specially,  as  in C programming: '\t' means TAB,
       '\r' means carriage return, '\n' means newline,  and  '\b'
       means  bell.    Any  octal  value  can  be  specified with
       '\nnn', where nnn is any positive octal number  less  than
       0400.  Any hexadecimal value can be specified with '\xnn',
       where nn is any positive hexadecimal number less  than  or
       equal to 0xff.

     colon-separated hexadecimal list

       A list of hexadecimal octet values, separated  by  colons,
       may be specified as a data expression.

So to match something like VLAN 1 Port 4, you could use the string "VLAN 1
Port 4" or encode each character in hex
56:4C:41:4E:20:31:20:50:6F:72:66:20:34

Try man ascii to give you conversion tables.

regards,
-glenn