New radio PIDs

[Ralph Corderoy]

Hi Vangelis,

> ...to begin with either "b0" or "p0".
> 
>  New radio PIDs like "w3csv1y9" or "w3csvnyc", beginning with "w3",
...
>     [bp]0[a-z0-9]{6}
> with
>     [bpw][a-z0-9]{7}

Other approaches, getting gradually more specific.

^[bpw][03][a-z0-9]{6}$
    But this allows b3.

^(b0|p0|w3)[a-z0-9]{6}$
    This is precise, but it's common to factor out alternations since
    each is tried in turn, so...

^([bp]0|w3)[a-z0-9]{6}$
    This is as precise.
    
The remaining problem is the `()' "capture" what matches for retrieval
by the program afterwards as $1, $2, ...  By introducing another set of
`()' we'd have affected the position of any that come afterwards in the
same regexp.  (None in this case.)  It's also inefficient to capture
when it's unnecessary.  `()' can be marked as non-capturing with `?:'.

^(?:[bp]0|w3)[a-z0-9]{6}$

These regexps aren't specific to Perl, BTW, but are useful with egrep,
awk, Python, etc.

-- 
Cheers, Ralph.
https://plus.google.com/+RalphCorderoy