Re: [Boston.pm] '/' =~ m"\/\b"; (bug?)

On 11/15/06, Carl Eklof <carleklof-/E1597aS9LQAvxtiuMwx3w@xxxxxxxxxxxxxxxx> 
wrote:
> Hi Guys n Gals,
>
> I have found some seemingly strange behavior that may
> be of interest to this list.
>
> My assumption was that the \b pattern in a regex would
> always match the beginning and end of a string (as
> documented in the perlre page). However on my build of
> 5.8.7 this is not the case if the character being
> matched at the beginning or the end is a
> "meta-character" ie. quotemeta would escape it. Also
> note that escaping the charcter doesn't seem to make a
> difference.

Actually that is NOT as documented in the perlre page.  And thoughts
to the contrary are a misreading of the documentation.

What the perlre page says is that there is an imaginary \W at the
beginning and end of the string.  The result is that if the first
character in the string matches \w, then \b will match at the start,
and if the last character matches \w, then \b will match at the end.

However if the first and/or last characters do *not* match \w, then
that is not a word boundary and \b will not match there.

[examples snipped]

> Maybe this is not a bug, and this is just another
> nuance of regexs' that I have not learned, but it
> looks very fishy.

It is definitely not a bug.  If the string is "...", then there are no
words, hence no word boundaries, therefore \b should not match at all.
 (And it does not.)

Conversely if the string is "hello" then there is a word, and it has
boundaries, and those boundaries should be matched by \b.  (And they
are, thanks to the "imaginary characters" discussed in the
documentation.)

> Any thoughts/wisdom?

See above.

Cheers,
Ben