Thanks to both Ben, and Ronald for correcting me. I had misunderstood the documentation.
I do expect that others may also think that using $string =~ /\b$sub_str\b/ is a reasonable way to match a substring on word-boundaries, or beginning/end of the string, but hopefully they will realize the nuanced effect of the "imaginary characters" at the beginning and end of the string, or find this post. Thanks again, -Carl --- Ben Tilly <[EMAIL PROTECTED]> wrote: > On 11/15/06, Carl Eklof <[EMAIL PROTECTED]> 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 > _______________________________________________ Boston-pm mailing list [email protected] http://mail.pm.org/mailman/listinfo/boston-pm
