SPUG: Word boundry regex treated differently by 5.6 and 5.005033

Ben Burnett benwa at ocentrix.com
Thu Apr 26 02:09:26 CDT 2001

At 05:51 PM 4/25/01 -0700, Colin Meyer wrote:
>More detail can be seen from the regex debugger:
>perl -M're debug' -le '$t = "abcdefg"; print pos $t while $t =~ m/\B\w/g'

I have to admin I haven't spent much time with the perl debugger I'll take 
a closer look at this.

>It is hard for me to decide if this is a new bug or a bug fix for an old
>problem. The camel says that /g causes the regex to "start the next
>match on the same variable at a position *just past* where the last
>match stopped." The older versions of Perl seem to be looking at the
>character that the last match ended on in order to determine the border
>or non-border properties of the character at pos($t). Well, it's either
>a bug with Perl, or a bug with its documentation. In either case, a
>report should be submitted with perlbug.

I think it's probably a bug with Perl itself.  I can't imagine this change 
in behavior was intentional.  I'll have to submit it in the morning.

>What sort of problem were you attempting to solve when you came across
>this one? ;-)

Here is an excerpt of code showing the regex hard at work in a motorcycle 
rental application CGI script.
                 # we need to give this request a registration number while 
we are here.  this number
                 # will be built out of the initials of each word in the 
applicants name, a unique session_key,
                 # the applicants state, and the first two letters of the 
city that the applicant is in
                         my $key = time();
                         $key .= "-" . getppid() or $LogH->append("couldn't 
getppid to add to session key");
                         my $request_id = $PASSED_VARS{'name'};
                         $request_id =~ s/\B\w//g;
                         $request_id =~ s/\W//g;
                         $request_id .= "-" . $key; # . "-";
                         # $request_id .= $PASSED_VARS{'state'} . "-";
                         # my $city_portion = $PASSED_VARS{'city'};
                         # $city_portion =~ m/^([\w]{2})/;
                         # $city_portion = $1;
                         # $request_id .= $city_portion ;
                         $request_id = uc($request_id);

I'll eventually work out some other form of unique id for these requests 
that isn't so verbose, but I wanted it to be human readable during testing.


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